Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community

Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community Xiangping Wang, Xiao Fu, Miaomiao Shi, Zhongtao Zhao, Shijin Li, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2546012/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Jul, 2023 Read the published version in Biological Invasions → Version 1 posted 4 You are reading this latest preprint version Abstract Invasive plant species severely threaten natural plant communities around the world, especially for islands. As introduction rates rise, novel species interactions appear within ecosystems. Studies that focus on invasive plant impacts on native plants, especially on native communities, remain largely unexplored and their conclusions are mixed. We constructed ten quantitative plant-pollinator interaction networks and calculated five network-level structure metrics (interaction evenness, linkage density, specialization, weighted connectance, and weighted nestedness) along an Asteraceae invasion gradient in the Yongxing Island community. We calculated the species-level nested contribution of each plant species in each network, and compared the nested contribution differences between invasive Asteraceae and non-Asteraceae species. Stigmas of three native and four invasive Asteraceae species were collected, and their pollen grains were identified. We analyzed invasive Asteraceae species impacts on native pollination network structure and native plant fitness. Both weighted nestedness and weighted connectance increased significantly as invasive Asteraceae became increasingly dominant. Invasive Asteraceae plants had higher nested contribution compared to native plants in most sites, and their nested contribution difference increased as the Asteraceae proportion increased. Furthermore, in native plant species, the proportion of conspecific pollen grains on stigmas decreased significantly, while the proportion of Asteraceae pollen grains on stigmas increased significantly with Asteraceae invasion level increased. For four invasive Asteraceae species, the proportion of conspecific pollen grains was significantly higher than heterospecific and other Asteraceae pollen grains on the stigmas. These results significantly add to our understanding of how the structure of plant-pollinator interaction networks changes concomitantly with plant invasion intensity. Invasive Asteraceae increase community stability and persistence, and negatively affect native plant fitness by influencing heterospecific pollen deposition on stigmas as invasion level increases. Invasive plants may greatly shape network structure and maintain community stability in oceanic island systems. Heterospecific pollen avoidance may be crucial mechanism facilitating Asteraceae invasion success within native communities, together with their ‘integration’, into plant-pollinator interactions on the Yongxing Island. Plant-pollinator interactions invasive Asteraceae plants network structure nested contribution pollen deposition invasive strategy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Invasive species seriously threaten global biodiversity and ecosystem functioning (Lambertini et al 2011 ). Plant-pollinator interactions vitally influence biodiversity maintenance and community stability (Bascompte and Jordano 2007 ). Invasive plants can affect native plant reproduction by decreasing flower visits rates and increasing heterospecific pollen deposition on stigmas (Bjerknes et al. 2007 ). Many researches have focused on how invasive plant affect the pollination of single native plant species (Morales and Traveset 2009 ; Vilá et al. 2011; Charlebois and Sargent 2017 ). However, the impacts of plant invasions on whole native communities and plant-pollinator interaction networks are still poorly understood (Stout and Tiedeken 2017 ; Valdovinos 2019 ). To more fully understand the consequences of increasing global plant species invasion, and to avoid further biodiversity loss and guarantee ecosystem functioning, it is quite important to study invasive plant effects on whole community-level interaction networks (Tylianakis and Morris 2017 ; van Kleunen 2018). Invasive plants are considered to be well integrated into native community if they attract the same pollinators as native plant species and receive equal or higher visitation rates than native plant species (Aizen et al. 2008 ; Montero-Castaño and Vilà 2017 ). Invasive plants also integrate successfully if they support plant-pollinator interaction network structure and their role within the network becomes equivalent to that of native species (Parra-Tabla et al. 2019 ; Corcos et al. 2020 ). For instance, the species-level metrics such as nested contribution of invasive and native plant species, can directly be compared. Nested contribution measures whether plant species increase or decrease overall network nestedness. Nestedness measures whether plant-pollinator interactions are established in a way which specialists interact with species subsets with which generalists interact (Bascompte and Jordano 2007 ). Nestedness maintains network stability and persistence, and is a crucial metric of network resilience and robustness in face of ecological disturbances (Bascompte et al. 2003 ; Memmott et al. 2004 ; Petanidou et al. 2008 ; Kaiser-Bunbury et al. 2010 ). Invasive plant species may alter the current network structure after they integrate into native plant-pollinator interaction networks, which ultimately affects community stability. For example, flowers of successful invasive plants usually are generalist that would attract a variety of pollinators (Memmott and Waser 2002 ); thus, they may affect interaction network evenness and connectance, particularly when flowers are abundant. The network-level parameters, such as connectance and nestedness, are closely related to community stability and persistence, while the species-level parameter nested contribution closely related to species extinction vulnerability (Saavedra et al. 2011 ; Saavedra and Stouffer 2013 ). A network approach therefore offers a particularly appropriate solution for evaluating changes in community structure and function as a response to ecological disturbances such as plant species invasions (Heleno et al. 2013 ; Traveset and Richardson 2014 ; Traveset et al. 2015 ). Some studies have evaluated invasive plant impacts on plant-pollinator interaction network structure by using network methods, but these results are still debated (Padrón et al. 2009 ; Kaiser-Bunbury et al. 2011 ; Stouffer et al. 2014 ; Parra-Tabla et al. 2019 ). Some of these studies suggest that invasive plant species affect the pollination network structures, such as connectance (Stout and Casey 2014 ), interaction evenness (Kaiser-Bunbury et al. 2011 ), modularity (Valdovinos et al. 2009 ; Albrecht et al. 2014 ), nestedness (Stouffer et al. 2014 ), and network level specialization (Stout and Casey 2014 ). In contrast, other studies have shown that invasive plants have only weak, or even zero, effects on network structure (Aizen et al. 2008 ; Padrón et al. 2009 ; Vilà et al. 2009 ; Tiedeken and Stout 2015 ; Traveset et al. 2015 ; Parra-Tabla et al. 2019 ). This apparent discrepancy in how invasive plants impact network structure may be because some studies only compared invaded and non-invaded communities, or the differences in the invasion intensity among study systems; however, this has seldom been considered (Kaiser-Bunbury et al. 2011 ; Tylianakis and Morris 2017 ). Therefore, to more fully understand invasive plant impacts on native plant-pollinator interactions, the variation in their effects across various invasive plant abundance levels must be studied. This knowledge may also help understand the conditions allowing invasive plants to quickly integrate into native pollination networks (Vilà et al. 2011 ; Tylianakis and Morris 2017 ). Furthermore, researches that considered both pollination network structure and species-level effects are still limited, and such studies may increase our understanding of invasive plant species effects on natural communities and ecosystems. Heterospecific pollen transfer among co-flowering plant species is prevalent both in invaded and non-invaded communities (Fang and Huang 2013 ; Arceo-Gómez et al. 2019 ; Johnson and Ashman 2019 ; Daniels and Arceo-Gómez 2020 ; Parra-Tabla et al. 2021 ), and negatively affects plant fitness (Ashman and Arceo-Gómez 2013 ; Arceo-Gómez and Ashman 2016 ; Ashman et al. 2020 ). For example, heterospecific pollen strongly and negatively affects plant reproductive success, resulting in ca. 20% decrease in seed set (Ashman and Arceo-Gómez 2013 ). Additionally, invasive heterospecific pollen donors reportedly lead to a higher decrease in fruit and seed set (Arceo-Gómez and Ashman 2016 ). The heterospecific pollen flow between invasive and native species might potentially influence invasive plant species integration into pollination networks. To completely integrate into native plant-pollinator networks, invasive plant species may need to avoid (by minimizing heterospecific pollen receipt), or tolerate (by minimizing reproductive impacts) the adverse impacts of heterospecific pollen deposition (Ashman and Arceo-Gómez 2013 ; Arceo-Gómez and Ashman 2016 ; Fang et al. 2019 ; Suárez-Mariño et al. 2019 , Parra-Tabla et al. 2021 ). Researches have recently suggested a higher capability of invasive plants to avoid or tolerate negative heterospecific pollen fitness impacts (Parra-Tabla et al. 2019 ; Suárez-Mariño et al. 2019 ; Parra-Tabla et al. 2021 ). Invasive Asteraceae plant Bidens pilosa , for example, has significantly higher tolerant to heterospecific pollen impacts than natives (Parra-Tabla et al. 2019 ; Suárez-Mariño et al. 2019 ). Therefore, heterospecific pollen avoidance or tolerance mechanisms may play a vital role in mediating invasive plant species integration into native pollination network (Suárez-Mariño et al. 2019 ; Parra-Tabla et al. 2021 ). However, empirical research for heterospecific pollen avoidance and tolerance as strategies helping plant species invasion and integration into pollination networks is rare until now. Islands harbor a large proportion of global biological diversity and are especially plentiful in endangered species (Kaiser-Bunbury et al. 2010 ; Traveset et al. 2015 ). However, most islands have received many invasive mainland species since being colonized by human (Kueffer et al. 2010 ; Montero-Castaño 2014). Alien plant species are more likely to invade island community, and more easily integrated into their plant-visitor interaction networks than continental networks (Padrón et al. 2009 ; Kaiser-Bunbury et al. 2011 ). Oceanic islands, in particular, are generally characterized with low insect diversity, as well as high generalization and nestedness when compared with mainland communities (Kaiser-Bunbury et al. 2010 ; Traveset et al. 2013 ; Traveset et al. 2015 ; Wang et al. 2020a , 2020b , 2021 ). Islands usually have small network size and more super-generalist species, which resulting in highly connected networks, i.e., more possible links between plant and pollinator species are implemented. Such pollination network characteristics of islands may facilitate invasive plant species integration into native community. On islands, low pollinator abundance and diversity may reduce pollinator redundancy; thus, their communities are potentially highly vulnerable when facing disturbances (Traveset and Richardson 2006 ). Many animal species that successfully settle remote islands often broaden their trophic niches for surviving in such low diversity ecosystems, thus interacting with more plant species than their mainland counterparts (Olesen et al. 2002 ; Wang et al. 2020a ). This feeding niche expansion tends to stabilize interaction networks in island systems (Traveset et al. 2015 ). Together with this, invasive plants may easily integrate into plant-pollinator interactions on oceanic islands because pollinators may also expand their feeding niche to these invasive plants. However, our knowledge of the mechanism underlying invasive plants integration into native plant-visitor interaction networks and their following impact, especially for oceanic island communities, remains limited. Like most islands around the world, the number of invasive plant species in the Yongxing Island (Paracel Islands) started rapidly increasing with human pressure in recent years. The main invasive plants in Yongxing Island are four Asteraceae species ( Bidens pilosa , Sphagneticola trilobata , Tridax procumbens , and Wedelia biflora ). Asteraceae have highly generalized floral traits, enabling them to utilize a wide variety of visitor species (Stouffer et al. 2014 ; Emer et al. 2015 ). Invasive Asteraceae Bidens pilosa , for instance, can attract ca. 60% of all the pollinators in the community (Parra-Tabla et al. 2019 ). These four Asteraceae plant species are all super-generalists and attracted the majority of the pollinator species on the Yongxing Island (Wang et al. 2020a , 2020b , 2021 ). However, the mechanisms that invasive Asteraceae plants integrated into the native Yongxing island ecosystem, and their specific effects on native plant pollination networks and fitness are little to known until now. Here, we constructed ten quantitative plant-pollinator interaction networks to explore invasive Asteraceae plants effects on native plant-pollinator interaction network structures and plant fitness on the Yongxing Island. Material And Methods Study sites and periods Paracel Islands (15°46′-17°08′N, 110°11′-112°54′E) are a group of coral reefs in the tropical ocean on the continental slope of the South China Sea, and are located in the southeast of Hainan Island. The Yongxing Island (16°50.1′N, 112°19.8′E) has an area of 2.6 km 2 and is the largest island of this archipelago (for more details on its location, see Wang et al. 2020a ). In recent years, four Asteraceae species ( B. pilosa , S. trilobata , T. procumbens , and W. biflora ) have gradually started to invade this island due to human activity. We selected ten sites along an Asteraceae dominance gradient which defined as the proportion of Asteraceae flowers to the whole number of flowers, and the proportion values varied from 0–56%. Ten 10 m x 10 m quadrats were located in each of the ten sites and at least 1000 m away from one another. The probability of movement of flower visitors among ten sites is extremely low because their limited average flying capacity on the island. Thus, each site could treat as an independent species assemblage. We collected the field data of flowering plants and their potential pollinators between 2 July and 30 August 2018. Plant species flowering patterns did not change during the two continuous months, and all visitor species were active for the whole duration of the study. Floral Abundance We assessed the floral abundance by recording the number of open flowering units for each plant species in the ten quadrats. The number flowers was counted within each quadrat for each flowering plant species, excluding wind-pollinated grasses. We defined flowering units as single flowers for most species, while for Asteraceae and Euphorbiaceae, the whole inflorescence was recorded as one flowering unit. Asteraceae invasion degree at each site was defined as the proportion of Asteraceae flowers in each quadrat. We calculated the proportion as the number of Asteraceae flowers divided by the entire number of open flowering units per quadrat. Pollination Observation Pollination observation was conducted on windless sunny days between 9:00 h and 16:00 h. Visitation rate was quantified for all the native and invasive Asteraceae plant species in each quadrat. Each site was observed for one day for each field observation round, and we conducted four rounds in total. The total observation time was about 25 hours per site. We recorded the visits to the flowers of each plant species during each 30 min observations. Only visits that visitor contacted with the reproductive organ (i.e., anther and/or stigma) of a flower for more than 2 s were recorded for each observation interval. If the same visitor individual return back to visit the same flower, such behavior was recorded as a new visit for the plant. All flower visitors found to be feeding on flowers were recorded, but ignoring their visitation efficacy. Opening flower numbers of each plant species in each site were counted before the pollinator observation. Pollinator visitation rate was measured as the average numbers of recorded visits/flower/hour during the observation periods. All native and invasive Asterace plant species and pollinator species in the Yongxing island community have been identified to the species level in our previous study (Wang et al., 2020a , 2020b , 2021 ). Thus, in this study, the visitation rate of each pollinator species to each native and invasive Asteraceae plant species could be both accurately recorded in the field. Pollination Networks For each site, we conducted one quantitative plant-pollinator network using pollinator species visitation frequencies to each native and invasive Asteraceae plant species as a surrogate of interaction strength. Metrics elucidating network structural properties were calculated to examine the changes of the network structure along the Asteraceae invasion gradient. Interaction evenness measured the frequency uniformity of network interactions. Linkage density measures the marginal weighted diversity of interactions of each species. Network-level specialization (H 2 ′) describes to which degree observed interactions deviate from those expected for a given marginal amount of species. Weighted connectance measures the portion of realized interactions happening within the networks, increases with network generalization. Weighted nestedness measures the interaction degree of specialized species within the network, considering interaction frequencies. Nested contribution of Asteraceae and non-Asteraceae plant species were calculated for each site. Some inherent characteristics, for example, the number of interaction species (i.e. matrix size) and sampling intensity could both influence network metrics (Fründ et al. 2016 ). Thus, metric significance was estimated by comparison with the Patefield null model networks, which fixed the network size and marginal total, and randomly shuffling interactions. For each network-level metric, the 95% confidence interval from 1000 simulated values was assessed. If a metric value did not overlap with the confidence interval, then it was considered significant. All network-related metrics were calculated using the bipartite package in R 4.1.3. Pollen Deposition On Stigma To evaluate invasive Asteraceae effects on the pollen grains deposition of native plant species in the same community, we used three native plant species ( Canavalia maritima , Scaevola taccada , and Tribulus cistoides ) that were present in more than three sites and quantified the number of conspecific, heterospecific, and Asteraceae pollen grains deposited on plant stigmas. C. maritima has purple and restrictive flowers. S. taccada has white and zygomorphic flowers with a spilt corolla tube ca. 18 mm in length. T. cistoides has open, yellow, and actinomorphic flowers. Among the three native plant species, T. cistoides has a similar flower shape and color compared with the invasive Asteraceae plant species. The flower shape of the four Asteraceae and three native plant species are shown in Figure S1. All three native plant species shared flower visitors with Asteraceae, and might strongly compete with Asteraceae. After observation, we collected 15–20 stigmas for each native plant species per quadrat that contained these species. For three native plant species, stigmas from 150 flowers were gathered and stored separately in FAA solution (formalin, glacial acetic acid, and 70% ethanol in a 1: 1: 18 ratio) in clean microcentrifuge tubes. Furthermore, we collected 50–55 stigmas for each Asteraceae plant species across the ten quadrats, and an overall total of 209 Asteraceae stigmas were stored. In the laboratory, each stigma was softened in 8 mol/l NaOH solution for 4 hours and placed on a clean slide. Pollen grains that dropped from the stigma into the solution were centrifuged and transferred with pipette from the bottom 50 µl of supernatant to another clean slide. For seven plant species, conspecific, heterospecific, and Asteraceae pollen grains on each slide were detected using a light microscope (BX41, Olympus) and identified by comparison to a field pollen reference library based on morphological characteristics such as shape and size. Furthermore, invasive Asteraceae plant pollen have special shape which clearly different from all other plant species, and thus can easily be identified, thus we have confidence in regarding the quantification of their pollen grains. We recorded the numbers of conspecific, heterospecific, and Asteraceae pollen grains for each stigma. The pollen g rains of four Asteraceae plant species were similar in shape, but differed in size; thus, their pollen grains could be distinguished under light microscope. We did not distinguish the species of other heterospecific pollen since it was not the focus of this study. The proportion of conspecific, heterospecific, and Asteraceae pollen grains was also calculated for three native and four Asteraceae plant species. Statistical Analyses To determine flower visitor floral preferences along the Asteraceae invasion gradient, resource selection null model was used to detect whether the floral visitation rate of each plant species were higher or lower than expected based on their flower abundance by using the econullnetr package in R (Vaughan et al., 2018 ). The resource selection null model assumes that the visitation rates of plant species in the community are proportional to their floral abundance. Generalized linear mixed models were conducted for each response to assess whether the Asteraceae invasion gradient influenced the Asteraceae and non-Asteraceae plants′ nested contribution, and the interactions between species, which were higher or lower visitation rate than expected based on floral abundance. The models were run using a binomial error distribution with a logit link function for pollen proportion. To examine how network metrics changes along the Asteraceae invasion intensity, we used generalized linear mixed models to analyze Asteraceae proportion impacts on pollination network structure (interaction evenness, linkage density, network-level specialization, weighted connectance, and weighted nestedness). All models included Asteraceae flower proportion as fixed effect, and site as a random factor. One-way ANOVA was used to test for difference in the proportion of conspecific, heterospecific, and Asteraceae pollen grain deposition on stigma among four/three sites to evaluate Asteraceae invasion effects on the pollen deposition of three native plant species in the same community. We also used One-way ANOVA to compare the proportional differences in conspecific, heterospecific, and Asteraceae pollen grain deposition on stigmas in each Asteraceae plant species. All data were analyzed using the lme4 and bipartite packages in R 4.1.3. Results In the ten sites, we sampled 37 plant species belonging to 21 plant families and 35 pollinator species. Lists of the plant and pollinator species are shown in supplementary table 1 and Table 2 , respectively. The number of plant and pollinator species, interaction evenness, linkage density, network-level specialization, weighted connectance, and weighted nestedness per site are shown in Table 1 . Most pollinators were Hymenoptera (45.7%), followed by Lepidoptera (28.6%), Diptera (22.9%), and Passeriformes (2.9%). Table 1 The proportion of Asteraceae flowers and the values of network-level metrics for quantitative plant-pollinator networks in ten sites. Asterisks represents network metrics which are significant, i.e., do not overlap null model expectations (95% confidence interval). Site (proportion of Asteraceae flowers) Plant species number Pollinator species number Interaction evenness Linkage density Specialization (H 2 ′) Weighted connectance Weighted nestedness 1 (0) 8 21 0.46 * 2.79 * 0.55 * 0.10 * 0.34 * 2 (0.02) 6 8 0.40 * 1.54 * 0.74 * 0.11 * 0.09 * 3 (0.06) 6 14 0.55 * 2.58 * 0.54 * 0.13 * 0.24 * 4 (0.14) 9 20 0.52 * 3.25 * 0.39 * 0.11 * 0.47 * 5 (0.17) 8 17 0.65 * 3.31 * 0.63 * 0.13 * 0.20 * 6 (0.21) 5 17 0.44 * 2.41 * 0.42 * 0.11 * 0.27 * 7 (0.25) 8 15 0.61 * 3.45 * 0.44 * 0.15 * 0.51 * 8 (0.33) 9 14 0.49 * 3.02 * 0.52 * 0.13 * 0.66 * 9 (0.45) 7 16 0.53 * 2.97 * 0.51 * 0.13 * 0.31 * 10 (0.56) 5 10 0.48 * 2.24 * 0.55 * 0.15 * 0.73 * Table 2 Five network-level quantitative metrics in ten sites, comparing observed values to the 95% confidence limits from the null model and including the standardized effect size (SES). Site Interaction evenness Linkage density Specialization (H2′) Weighted connectance Weighted nestedness Test SES Test SES Test SES Test SES Test SES 1 Higher 5.76 ns 0.85 ns 0.30 ns 0.85 Higher 12.86 2 ns -0.80 Lower -1.93 ns 1.35 Lower -1.93 Higher 2.23 3 Higher 2.47 ns 0.04 ns 0.19 ns 0.04 ns -0.14 4 ns 1.39 Higher 2.10 ns -1.88 Higher 2.10 Higher 7.36 5 ns -0.90 ns -0.77 ns 0.77 ns -0.77 Higher 2.55 6 ns 1.18 ns 0.83 ns -0.68 ns 0.83 Higher 7.49 7 Higher 3.39 Higher 2.34 ns -0.75 Higher 2.34 Higher 7.57 8 Higher 2.04 Higher 2.76 ns -0.85 Higher 2.76 Higher 9.27 9 ns 0.79 ns 0.39 ns -0.06 ns 0.39 Higher 2.86 10 Higher 3.38 ns -0.06 ns 0.20 ns -0.06 Higher 6.98 Comparison Of Networks Using The Resource Selection Null Model Weighted nestedness values were higher than expected in nine sites, except in site three, while specialization values did not differ from expected values for all sites (Table 2 ). None of the plant-pollinator links were weaker than expected based on flower abundance in all ten sites (Fig. 1 ). For non-Asteraceae pollinator links, 28.7% ± 4.0% were stronger than expected based on flower abundance. For Asteraceae pollinator interactions, 31.1% ± 5.7% were stronger than expected. The Asteraceae flower proportion did not affect the stronger link proportion for either non-Asteraceae (df = 8, t = -1.376, P = 0.206) or Asteraceae (df = 7, t = -1.158, P = 0.285) plants (Fig. 2 ). The Impact Of Invasive Asteraceae On Pollination Network Structure Both weighted connectance (df = 8, t = 2.697, P = 0.027) and weighted nestedness (df = 8, t = 2.569, P = 0.033) increased significantly with the proportion of Asteraceae increased (Fig. 3 ; Table 3 ). Interaction evenness, linkage density, and specialization did not significantly change with the proportion of Asteraceae increased (Table 3 ). Table 3 Results of the generalized linear mixed models used to test the effects of the proportion of Asteraceae flowers on five quantitative network-level metrics. The values heighted in bold are statistically significant based on likelihood ratio tests (P < 0.05). Network metric Std.Error df t P Interaction evenness 0.144 8 0.357 0.730 Linkage density 1.111 8 0.367 0.723 Specialization (H 2 ′) 0.193 8 -0.723 0.490 Weighted connectance 0.024 8 2.697 0.027 Weighted nestedness 0.292 8 2.569 0.033 Comparison Of Nested Contribution Between Invasive Asteraceae And Non-asteraceae Plants Invasive Asteraceae plants were higher in nested contribution compared to native plants in most sites, even though differences were not always significant (Table S3, Figure S2). The pollination network nested contribution difference between Asteraceae and non-Asteraceae plants increased as the proportion of Asteraceae increased (df = 7, t = 2.61, P = 0.035, Fig. 4 ). The Impact Of Invasive Asteraceae On Stigma Pollen Loads In Three Native Plant Species For C. maritima , we totally recorded 3838 pollen grains on 50 stigmas from three sites, 97.0% of which were conspecific, 2.8% of which were heterospecific, and 0.2% of which were Asteraceae pollen. The proportion of conspecific pollen grains on stigmas decreased while the proportion of heterospecific pollen grains increased significantly as Asteraceae invasion level increased (Table 4 , Fig. 5 ). Table 4 Results of the generalized linear mixed models used to test the effects of Asteraceae on the proportion of conspecific pollen (CP), heterospecific pollen (HP) and Asteraceae pollen (AP) deposition on stigmas of co-flowering native species of C. maritime, S. taccada and T. cistoides separately. The values highlighted in bold are statistically significant based on likelihood ratio tests (P < 0.05). Species Response Sum Sq Mesn Sq df F P C. maritima Proportion of CP 0.19 0.10 2 8.60 0.0007 Proportion of HP 0.10 0.05 2 5.72 0.006 Proportion of AP 0.02 0.01 2 1.44 0.247 S. taccada Proportion of CP 0.13 0.04 3 5.96 0.002 Proportion of HP 0.04 0.01 3 2.17 0.104 Proportion of AP 0.02 0.01 3 2.99 0.04 T. cistoides Proportion of CP 3.25 1.08 3 37.53 < 0.0001 Proportion of HP 0.06 0.02 3 1.03 0.389 Proportion of AP 2.46 0.82 3 23.9 < 0.0001 For S. taccada , we totally recorded 10421 pollen grains on 52 stigmas from four sites, 98.7% of which were conspecific, 0.5% of which were heterospecific and 0.8% of which were Asteraceae pollen. As the Asteraceae invasion level increased, the conspecific pollen grain proportion on stigmas decreased, while the Asteraceae pollen grain proportion increased significantly (Table 4 , Fig. 5 ). For T. cistoides , we totally recorded 8433 pollen grains on 50 stigmas from four sites, 45.1% of which were conspecific, 9.7% of which were heterospecific, and 45.2% of which were Asteraceae pollen. As the Asteraceae invasion level increased, the conspecific pollen grain proportion on stigmas decreased, while the Asteraceae pollen grain proportion increased significantly (Table 4 , Fig. 5 ). Pollen Loads On Stigmas In Four Invasive Asteraceae Plants For four Asteraceae plant species, namely B. pilosa , S. trilobata , T. procumbens , and W. biflora , we counted a total of 5207, 6577, 4183, and 5519 pollen grains on 53, 50, 53, and 53 stigmas, respectively, across ten sites (not all sites). A total of 99.5%, 95.5%, 99.6%, and 98.2% were conspecific, 0.2%, 2.8%, 0.1%, and 1.6% were heterospecific, and 0.3%, 1.8%, 0.3%, and 0.1% were other Asteraceae pollen grains, respectively. In all four Asteraceae plant species the conspecific pollen grain proportion was significantly higher compared to heterospecific and other Asteraceae pollen grains deposited on the stigmas (all P < 0.001, Fig. 6 ). Discussion The plant-pollinator interaction network structures clearly changed as the Asteraceae invasion level increased. Both weighted connectance and weighted nestedness increased significantly as the proportion of Asteraceae increased. These results add significantly to our understanding of how plant-pollinator interaction network structures vary with the plant invasion gradient on oceanic island. Moreover, invasive Asteraceae plants had a higher nested contribution compared to native plants, and this difference increased as the Asteraceae proportion increased. This implied that invasive Asteraceae plants may help to shape pollination network structure. In all three native plant species the conspecific pollen grain proportion on stigmas decreased significantly as the Asteraceae invasion level increased. Also, in two native plant species the Asteraceae pollen grain proportion on the stigmas increased significantly as the Asteraceae invasion level increased. In all four Asteraceae invasive plant species the conspecific pollen grain proportion was significantly higher compared to heterospecific and other Asteraceae pollen grains deposited on the stigmas. These results provide insight into how invasive plants influence plant-pollinator interactions, as well as native plant pollen deposition on Oceanic Island. Generally, this study revealed that plant-pollinator interaction network structure changed as invasive plant intensity increased, thereby resulting in significant negative effects on native plant reproduction. In the Yongxing island community, invasive Asteraceae plants enhance a nested pattern and increase network connectance, but did not significantly affect other network parameters, such as interaction evenness, linkage density, and specialization as Asteraceae invasion level increased. This result supports previous findings that network connectance is positively related to invasive plant abundance (Stout and Casey 2014 ). In contrast, other research suggested that invasive plants had a low impact on plant-pollinator network structure (Traveset et al. 2015 ; Parra-Tabla et al. 2019 ). Super generalist pollinators can facilitate invasive plant integration into native pollination network, and support network structure by increasing network connectance and nestedness in invaded communities (Albrecht et al. 2014 ; Parra-Tabla et al. 2021 ). This could also be the case in our community where the super generalist pollinator Apis cerana visits most of the flowers on the Yongxing island and thus contributes to a large proportion of flora visits (Wang et al. 2020a , 2020b , 2020c ), even frequently visiting a bird pollinated plant species (Wang et al. 2020d ), and may help to structure pollination networks. A new research suggested that invasive plant species interact with more generalist pollinator species, whereas specialist pollinators more severely depend on native plant species (Parra-Tabla and Arceo-Gómez 2021 ). In our community, however, some other generalist pollinators, such as Braunapis puangensis , Ceratina lieftincki , and Micromeriella marginella , as well as specialized pollinators, such as butterflies and hawkmoths, also frequently visited Asteraceae plants in the generalized community (Wang et al. 2020a , 2020b , Wang et al. 2021 ), which also increased pollination network nestedness and connectance and may lead to more generalist networks in the oceanic island community. Therefore, invasive Asteraceae plants act as super-generalists, thereby attracting most pollinator species and notably increasing network nestedness (Bartomeus et al. 2008 ; Russo et al. 2019 ). Network-level connectance and nestedness are usually used to describe plant-pollinator interaction network structures, which are useful and important topological metrics for representing the degree to which communities are reshaped in face of plant invasions (Campbell et al. 2022 ). Our findings highlight the potential importance of super generalist pollinators and invasive Asteraceae species in structuring pollination networks in invaded oceanic island communities. The fact that network weighted connectance and nestedness increased with invasive Asteraceae abundance in our study suggests that invasive generalized plants could enhance oceanic island community stability and resilience. The nested contribution of invasive Asteraceae plants was higher compared to non-Asteraceae plants, and this difference increased as Asteraceae abundance increased. Our findings contrast with works in Oʻahu (Hawaiian Archipelago), the data of which showed that native and invasive plants contribute equally to nestedness in seed dispersal networks (Parra-Tabla et al. 2019 ; Vizentin-Bugoni et al. 2021 ). Our results support the findings of Stouffer et al. ( 2014 ), namely that networks where invasive plants are present are characterized by higher nestedness based on a global database of empirical pollination networks. Furthermore, similar findings have also been reported recently in urban green spaces, suggesting that exotic plant species contribute more to network nestedness than native plant species (Zaninotto et al. 2023 ). Nested pattern in plant-pollinator networks suggests a more stable community structure as functional redundancy is high, and thus more generalist species being able to interact with the partners of lost specialists (Thébault and Fontaine 2010 ). Thus, invasive Asteraceae may contribute more to increasing functional redundancy by increasing network nestedness, which is expected to enhance community stability, than non-Asteraceae plants. This suggests that invasive Asteraceae plants play a more important network stabilization role than native plants, and also provide additional resources for native pollinators in the Yongxing island community. In our study, the nested contribution differences between Asteraceae and non-Asteraceae plants increased as Asteraceae abundance increased, thereby implying its network importance. Network species importance is reported to be positively associated with plant abundance (Vizentin-Bugoni et al. 2021 ). If flowers of invasive plant species are open and unrestrictive which can attract a wide range of pollinator species, they may contribute more to increase network nestedness. It is well known that species which contribute more to network nestedness are also vital for the entire network’s persistence (Saavedra et al. 2011 ). Previous work showed that invasive plant species tend to interact with specialist pollinators which also weakly contribute to network nestedness (Stouffer et al. 2014 ). Similarly, in our community, the generalized Asteraceae plants not only interacted with generalized pollinators, such as bees ( Apis cerana ), but also frequently interacted with specialists, such as hoverflies (e.g., Asarkina porcina ) and butterflies ( Zizina otis ). Theoretical study has proposed that specialists are the most vulnerable to extinction, but as a weaker nestedness contributor can balance this consequence (Saavedra et al. 2011 ). Therefore, invasive Asteraceae plants may have benefited the vulnerable specialist visitors on isolated oceanic islands. Invasive Asteraceae pollen was detected on native plant species stigmas, supporting that heterospecific pollen deposition was also common in invaded communities (Johnson and Ashman 2019 ; Parra-Tabla et al. 2021 ). A meta-analysis of 76 studies showed that invasive plants both positively facilitate and negatively reduce native pollination (Charlebois and Sargent 2017 ). For example, Parra-Tabla et al. ( 2021 ) found that alien heterospecific pollen significantly reduces pollination success, for example, by affecting native species’ pollen tube growth, in coastal communities, while Lopes et al. ( 2022 ) found that heterospecific pollen deposition causes a higher reproductive success through increased conspecific pollen deposition. In our study, the conspecific pollen proportion on stigmas decreased significantly in C. maritima , S. taccada , and T. cistoides , and the Asteraceae pollen grain proportion on stigmas increased significantly in S. taccada and T. cistoides with increasing Asteraceae invasion, indicating that invasive Asteraceae might negatively affect pollination service quality for native plant species. This effect is likely to be due to the high number of shared pollinators between invasive Asteraceae and native plants. Moreover, the Asteraceae pollen proportion on the stigmas of T. cistoides was higher than the other two native species, indicating that invasive Asteraceae might have stronger negative effects on T. cistoides . This may be explained by floral trait differences among three native plant species. T. cistoides has yellow and radially symmetric flowers, and is very similar to S. trilobata and W. biflora . These similar floral traits (flower shape and color) between native and invasive plants can reinforce negative impacts of invasive plants on native plant species reproduction success (Morales and Traveset 2009 ). In contrast, C. maritima and S. taccada have bilaterally symmetrical, purple, and white flowers; thus, the Asteraceae pollen proportion on these stigmas was both less than 1%. This result was consistent with a recent research that showed that species with yellow flowers could receive more heterospecific pollen than species with purple flowers (Parra-Tabla et al. 2021 ). Heterospecific pollen that from invasive plants can decrease fruit and seed set of plants to a greater degree than heterospecific pollen that from native plants (Arceo-Gómez and Ashman 2016 ). Therefore, invasive Asteraceae plant species may indirectly and detrimentally affect native plant reproduction, especially for plants that share similar floral traits with them. Alien species can easily invade native communities if they have greater capacity to donate, but avoid, heterospecific pollen compared to native plants (Parra-Tabla et al. 2021 ). Our findings support this theory by revealing pollen load differences between invasive Asteraceae and native plants. Specifically, the invasive Asteraceae pollen deposited on the stigmas of the native plant T. cistoides were as much as 45.2%. Similarly, in four invasive Asteraceae plant species, in excess of 95% of the pollen grains deposited on their stigmas were conspecific pollen. Furthermore, the conspecific pollen proportion on stigmas reached up to 99.5% and 99.6% in B. pilosa and T. procumbens , respectively. These results consistent with a recent research that invasive plant species are more frequently heterospecific pollen donors, and native plant species are more frequently heterospecific pollen recipients (Parra-Tabla et al. 2021 ). Low heterospecific pollen loads in four Asteraceae plants suggested that avoidance of heterospecific pollen receipt may be a vital strategy determining whether they can successfully invade and integrate into native pollination networks on Yongxing Island. Overall, our results suggest that higher heterospecific pollen donation, along with a fairly low heterospecific pollen deposition on invasive Asteraceae plant stigmas may aid in their successful invasion of native communities. This highlights the essential for future researches to assess their importance and functional role, especially in heterospecific pollen transfer networks (Parra-Tabla et al. 2021 ). Researches have reported that plant-pollinator interaction networks had strong resistance to invasive plant species (Vilà et al. 2009 ; Parra-Tabla et al. 2019 ). However, our findings show that invasive plants can change pollination network structures and influence community robustness via increasing the network-level connectance and nestedness. Moreover, these structural network changes could enhance community stability, which seems beneficial for the whole system. On the other hand, our findings suggested that invasive plants may potentially affect native plant species reproduction, especially for plants that share their floral traits, by increasing heterospecific pollen deposition in the community. Invasive Asteraceae received few heterospecific pollen grains, which may be a strategy that helps them successfully invade native communities. To better understand the invasive plant species impacts on natural communities, it is necessary for integrative researches that simultaneously considered invasive species effects on pollination network structures, heterospecific pollen deposition, and native plant species reproduction. For example, a recent research suggested that heterospecific pollen transfer networks among plant species continue relatively constant regardless of plant invasion degree (Parra-Tabla et al. 2021 ). Therefore, in order to more fully understand the ecological and evolutionary consequences of changes in pollination network structures, integrating information including all pollination process levels is important. Declarations Acknowledgements We thank Tong zeng, Mingsong Wu for their worthy help in the field. We thank the logistical support on the Yongxing Island from Xisha Ocean observation and research station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China. This study was supported by the National Natural Science Foundation of China (grant number 32271613, 32170232), the Natural Science Foundation of Guangzhou (grant number 202201010218), the National Key Research and Development Program of China (grant number 2021YFC3100405) and the Science and Technology Basic Works Program of Ministry of Science and Technology of China (grant number 2019FY202100). Conflict of interest All authors declare no conflict of interest and gave final approval for publication. References Aizen, M. A., Morales, C. L., Morales, J. M. (2008) Invasive mutualists erode native pollination webs. PLoS biology , 6(2), e31. Albrecht, M., Padrón, B., Bartomeus, I., Traveset, A. 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Supplementary Files FigureS1.pdf Figure S1.Four invasion Asteraceae plant species (a-d) and three native plant species (e-g) in the Yongxing island community. (a) Bidens pilosa ; (b) Sphagneticola trilobata ; (c) Tridax procumbens ; (d) Wedelia biflora ; (e) Canavalia maritime ; (f) Scaevola taccada ; (g) Tribulus cistoides . FigureS2.pdf Figure S2.The nestedcontribution of non-Asteraceae and Asteraceae plant species in ten sites. Asterisks represents the differences are significant (P < 0.05). 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2546012","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":174531094,"identity":"772d2f5f-e674-4fe8-8f71-d68a04877864","order_by":0,"name":"Xiangping Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIiWNgGAWjYDACZjApAeVVMDAYkKjlDDFaUABjGxFaDI4zP3v4dYdFnnxEMpAxr07enH8B44cfDHZ5uLRINrOZG8uekSg2vJEGZGw7bLhzxgNmyR6G5GJcWviZGcykJdskEjfOTgAyth1IMLhxgEGageFAYgMOLWzM7N+gWtKBjDl1IC3Mv/Fp4WfmMZP8CNQyXzoHyGhgTjA438CG1xbJZp4yacYzEokb5N+USTMcA/mFsc2yxyAZpxaD88e3Sf7cUZc4vwfI+FEDCrHDh2/8qLDDqQUEmHmBsgYHgAweEFcCpJhA7DD+BKqRB2LGH2DvHcCvfBSMglEwCkYcAACFVlbjsoe+wQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-0645-6370","institution":"South China Botanical Garden","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Xiangping","middleName":"","lastName":"Wang","suffix":""},{"id":174531095,"identity":"654f4824-6dd6-4c27-9a17-a3e8d626172c","order_by":1,"name":"Xiao Fu","email":"","orcid":"","institution":"Ningxia Yunwu Mountain National Natural Reserve","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Xiao","middleName":"","lastName":"Fu","suffix":""},{"id":174531096,"identity":"dc866777-2c59-4a28-a41d-97638b3f2993","order_by":2,"name":"Miaomiao Shi","email":"","orcid":"","institution":"South China Botanical Garden","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Miaomiao","middleName":"","lastName":"Shi","suffix":""},{"id":174531097,"identity":"ec657232-6f68-4ed9-98e5-21896ceadd0c","order_by":3,"name":"Zhongtao Zhao","email":"","orcid":"","institution":"South China Botanical Garden","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhongtao","middleName":"","lastName":"Zhao","suffix":""},{"id":174531098,"identity":"5a593b76-fed2-4ee6-8852-5d7139c8e31c","order_by":4,"name":"Shijin Li","email":"","orcid":"","institution":"South China Botanical Garden","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Shijin","middleName":"","lastName":"Li","suffix":""},{"id":174531099,"identity":"0be817bf-a37d-4333-9b1e-9a7efdf442c4","order_by":5,"name":"Tieyao Tu","email":"","orcid":"","institution":"South China Botanical Garden","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Tieyao","middleName":"","lastName":"Tu","suffix":""}],"badges":[],"createdAt":"2023-02-03 09:17:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2546012/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2546012/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10530-023-03129-w","type":"published","date":"2023-07-18T21:42:45+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":32776875,"identity":"fc77f86c-3908-4a83-8051-49a6438ede2b","added_by":"auto","created_at":"2023-02-10 22:29:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":37081092,"visible":true,"origin":"","legend":"\u003cp\u003ePlant-pollinator interaction networks in ten quadrats on the Yongxing island, (a) to (j) present site1to site 10, respectively. The rectangles represent pollinator species (top row) and plant species (bottom row), and the connecting lines represent interactions between plant and pollinator species. Link widths represent the observed visitation frequency of interactions, with red lines stronger than expected under null model. Plant species are colour-coded as follows: black: non-Asteraceae plant species, green: Asteraceae plant species. Full names of plant and pollinator species are available in Table S1 and Table S2.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/77cd25fdc26f9768575e1e7d.png"},{"id":32776865,"identity":"8c89c9e8-6664-4f94-8189-1413d201c7d9","added_by":"auto","created_at":"2023-02-10 22:29:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":62482,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between the proportion of Asteraceae flowers in the site and the proportion of stronger links of non-Asteraceae/Asteraceae than expected by flower abundance.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/54486df2d332315b48f8409a.png"},{"id":32777144,"identity":"e426b7fc-4217-4c2a-a1e1-e1ea520fb0e8","added_by":"auto","created_at":"2023-02-10 22:37:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":596962,"visible":true,"origin":"","legend":"\u003cp\u003eRelationships between the proportion of Asteraceae flowers in the community and network-level (a) weighted nestedness; and (b) weighted connectance. The black lines represent predictions based on the minimum adequate GLMMs and the grey bands represent the 95% confidence intervals.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/edc6c9ec3c22c1f87868700d.png"},{"id":32777147,"identity":"330950ef-bc3d-4929-80a5-8a931ea8ca2f","added_by":"auto","created_at":"2023-02-10 22:37:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":80401,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between the proportion of Asteraceae flowers and the difference of nestedcontribution to the pollination network between Asteraceae and non-Asteraceae plant species.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/237e25a44ec391b673da843b.png"},{"id":32777393,"identity":"0bd743ed-039d-46bb-971d-a9f4f5dd8b42","added_by":"auto","created_at":"2023-02-10 22:45:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":183061,"visible":true,"origin":"","legend":"\u003cp\u003eRelationships between the proportion of Asteraceae flowers and the proportion of pollen grains (conspecific, heterospecific and Asteraceae pollen) deposited on stigmas in \u003cem\u003eC. maritime\u003c/em\u003e,\u003cem\u003e S. taccada\u003c/em\u003e and \u003cem\u003eT. cistoides\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/570547e904082409c97f3b45.png"},{"id":32776872,"identity":"b6c81061-da9f-4a60-9188-b1c292fb5a9e","added_by":"auto","created_at":"2023-02-10 22:29:26","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":52224,"visible":true,"origin":"","legend":"\u003cp\u003eThe proportion of conspecific, heterospecific, and others Asteraceae pollen grains deposited on the stigma in four invasion Asteraceae plant species. Asterisks represent the differences are significant (P \u0026lt; 0.001).\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/d881b0799652e376bc785c14.png"},{"id":44733658,"identity":"5c4ddf7b-b011-48c3-8c09-9ef7f8c73fff","added_by":"auto","created_at":"2023-10-16 22:09:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":948543,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/deb33a0c-c731-4cc8-8370-9895af41357a.pdf"},{"id":32776874,"identity":"26f8e8cc-2779-428f-b722-79c91b1a6db1","added_by":"auto","created_at":"2023-02-10 22:29:26","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":12868917,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure S1.\u003c/strong\u003eFour invasion Asteraceae plant species (a-d) and three native plant species (e-g) in the Yongxing island community. (a) \u003cem\u003eBidens pilosa\u003c/em\u003e; (b) \u003cem\u003eSphagneticola trilobata\u003c/em\u003e; (c) \u003cem\u003eTridax procumbens\u003c/em\u003e; (d) \u003cem\u003eWedelia biflora\u003c/em\u003e; (e) \u003cem\u003eCanavalia maritime\u003c/em\u003e; (f) \u003cem\u003eScaevola taccada\u003c/em\u003e; (g) \u003cem\u003eTribulus cistoides\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"FigureS1.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/615b86dd155e7c5f06e4954c.pdf"},{"id":32777148,"identity":"24cab8d2-350e-4dbd-bb72-9b86777a1e6f","added_by":"auto","created_at":"2023-02-10 22:37:26","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":1043301,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFigure S2.\u003c/strong\u003eThe nestedcontribution of non-Asteraceae and Asteraceae plant species in ten sites. Asterisks represents the differences are significant (P \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"FigureS2.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/1e178b7695bcdb7cdbeeaccf.pdf"},{"id":32776869,"identity":"4bc6936d-20f9-4267-96a7-bd26b6e7e282","added_by":"auto","created_at":"2023-02-10 22:29:26","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":15482,"visible":true,"origin":"","legend":"","description":"","filename":"TableS1.docx","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/aab151612519d71691d6a533.docx"},{"id":32776867,"identity":"014ed9c4-df7e-4f72-b3e0-02bbe9c5288d","added_by":"auto","created_at":"2023-02-10 22:29:25","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":15733,"visible":true,"origin":"","legend":"","description":"","filename":"TableS2.docx","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/2499fb01fa20eba66bcc10cc.docx"},{"id":32777145,"identity":"58637ea6-ae9c-4cda-bc36-1af7cfa60d19","added_by":"auto","created_at":"2023-02-10 22:37:25","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":15332,"visible":true,"origin":"","legend":"","description":"","filename":"TableS3.docx","url":"https://assets-eu.researchsquare.com/files/rs-2546012/v1/2685a509e6aabb46587017f8.docx"}],"financialInterests":"","formattedTitle":"Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community","fulltext":[{"header":"Introduction","content":"\u003cp\u003eInvasive species seriously threaten global biodiversity and ecosystem functioning (Lambertini et al \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Plant-pollinator interactions vitally influence biodiversity maintenance and community stability (Bascompte and Jordano \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Invasive plants can affect native plant reproduction by decreasing flower visits rates and increasing heterospecific pollen deposition on stigmas (Bjerknes et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Many researches have focused on how invasive plant affect the pollination of single native plant species (Morales and Traveset \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vil\u0026aacute; et al. 2011; Charlebois and Sargent \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, the impacts of plant invasions on whole native communities and plant-pollinator interaction networks are still poorly understood (Stout and Tiedeken \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Valdovinos \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). To more fully understand the consequences of increasing global plant species invasion, and to avoid further biodiversity loss and guarantee ecosystem functioning, it is quite important to study invasive plant effects on whole community-level interaction networks (Tylianakis and Morris \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; van Kleunen 2018).\u003c/p\u003e \u003cp\u003eInvasive plants are considered to be well integrated into native community if they attract the same pollinators as native plant species and receive equal or higher visitation rates than native plant species (Aizen et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Montero-Casta\u0026ntilde;o and Vil\u0026agrave; \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Invasive plants also integrate successfully if they support plant-pollinator interaction network structure and their role within the network becomes equivalent to that of native species (Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Corcos et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For instance, the species-level metrics such as nested contribution of invasive and native plant species, can directly be compared. Nested contribution measures whether plant species increase or decrease overall network nestedness. Nestedness measures whether plant-pollinator interactions are established in a way which specialists interact with species subsets with which generalists interact (Bascompte and Jordano \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Nestedness maintains network stability and persistence, and is a crucial metric of network resilience and robustness in face of ecological disturbances (Bascompte et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Memmott et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Petanidou et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Kaiser-Bunbury et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Invasive plant species may alter the current network structure after they integrate into native plant-pollinator interaction networks, which ultimately affects community stability. For example, flowers of successful invasive plants usually are generalist that would attract a variety of pollinators (Memmott and Waser \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2002\u003c/span\u003e); thus, they may affect interaction network evenness and connectance, particularly when flowers are abundant. The network-level parameters, such as connectance and nestedness, are closely related to community stability and persistence, while the species-level parameter nested contribution closely related to species extinction vulnerability (Saavedra et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Saavedra and Stouffer \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). A network approach therefore offers a particularly appropriate solution for evaluating changes in community structure and function as a response to ecological disturbances such as plant species invasions (Heleno et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Traveset and Richardson \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSome studies have evaluated invasive plant impacts on plant-pollinator interaction network structure by using network methods, but these results are still debated (Padr\u0026oacute;n et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Kaiser-Bunbury et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Stouffer et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Some of these studies suggest that invasive plant species affect the pollination network structures, such as connectance (Stout and Casey \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), interaction evenness (Kaiser-Bunbury et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), modularity (Valdovinos et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Albrecht et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), nestedness (Stouffer et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), and network level specialization (Stout and Casey \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In contrast, other studies have shown that invasive plants have only weak, or even zero, effects on network structure (Aizen et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Padr\u0026oacute;n et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Vil\u0026agrave; et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Tiedeken and Stout \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This apparent discrepancy in how invasive plants impact network structure may be because some studies only compared invaded and non-invaded communities, or the differences in the invasion intensity among study systems; however, this has seldom been considered (Kaiser-Bunbury et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tylianakis and Morris \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Therefore, to more fully understand invasive plant impacts on native plant-pollinator interactions, the variation in their effects across various invasive plant abundance levels must be studied. This knowledge may also help understand the conditions allowing invasive plants to quickly integrate into native pollination networks (Vil\u0026agrave; et al. \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tylianakis and Morris \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Furthermore, researches that considered both pollination network structure and species-level effects are still limited, and such studies may increase our understanding of invasive plant species effects on natural communities and ecosystems.\u003c/p\u003e \u003cp\u003eHeterospecific pollen transfer among co-flowering plant species is prevalent both in invaded and non-invaded communities (Fang and Huang \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Arceo-G\u0026oacute;mez et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Johnson and Ashman \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Daniels and Arceo-G\u0026oacute;mez \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and negatively affects plant fitness (Ashman and Arceo-G\u0026oacute;mez \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Arceo-G\u0026oacute;mez and Ashman \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Ashman et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). For example, heterospecific pollen strongly and negatively affects plant reproductive success, resulting in ca. 20% decrease in seed set (Ashman and Arceo-G\u0026oacute;mez \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Additionally, invasive heterospecific pollen donors reportedly lead to a higher decrease in fruit and seed set (Arceo-G\u0026oacute;mez and Ashman \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). The heterospecific pollen flow between invasive and native species might potentially influence invasive plant species integration into pollination networks. To completely integrate into native plant-pollinator networks, invasive plant species may need to avoid (by minimizing heterospecific pollen receipt), or tolerate (by minimizing reproductive impacts) the adverse impacts of heterospecific pollen deposition (Ashman and Arceo-G\u0026oacute;mez \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Arceo-G\u0026oacute;mez and Ashman \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Fang et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Su\u0026aacute;rez-Mari\u0026ntilde;o et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e, Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Researches have recently suggested a higher capability of invasive plants to avoid or tolerate negative heterospecific pollen fitness impacts (Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Su\u0026aacute;rez-Mari\u0026ntilde;o et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Invasive Asteraceae plant \u003cem\u003eBidens pilosa\u003c/em\u003e, for example, has significantly higher tolerant to heterospecific pollen impacts than natives (Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Su\u0026aacute;rez-Mari\u0026ntilde;o et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Therefore, heterospecific pollen avoidance or tolerance mechanisms may play a vital role in mediating invasive plant species integration into native pollination network (Su\u0026aacute;rez-Mari\u0026ntilde;o et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, empirical research for heterospecific pollen avoidance and tolerance as strategies helping plant species invasion and integration into pollination networks is rare until now.\u003c/p\u003e \u003cp\u003eIslands harbor a large proportion of global biological diversity and are especially plentiful in endangered species (Kaiser-Bunbury et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). However, most islands have received many invasive mainland species since being colonized by human (Kueffer et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Montero-Casta\u0026ntilde;o 2014). Alien plant species are more likely to invade island community, and more easily integrated into their plant-visitor interaction networks than continental networks (Padr\u0026oacute;n et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Kaiser-Bunbury et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Oceanic islands, in particular, are generally characterized with low insect diversity, as well as high generalization and nestedness when compared with mainland communities (Kaiser-Bunbury et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Traveset et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Islands usually have small network size and more super-generalist species, which resulting in highly connected networks, i.e., more possible links between plant and pollinator species are implemented. Such pollination network characteristics of islands may facilitate invasive plant species integration into native community. On islands, low pollinator abundance and diversity may reduce pollinator redundancy; thus, their communities are potentially highly vulnerable when facing disturbances (Traveset and Richardson \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Many animal species that successfully settle remote islands often broaden their trophic niches for surviving in such low diversity ecosystems, thus interacting with more plant species than their mainland counterparts (Olesen et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). This feeding niche expansion tends to stabilize interaction networks in island systems (Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Together with this, invasive plants may easily integrate into plant-pollinator interactions on oceanic islands because pollinators may also expand their feeding niche to these invasive plants. However, our knowledge of the mechanism underlying invasive plants integration into native plant-visitor interaction networks and their following impact, especially for oceanic island communities, remains limited.\u003c/p\u003e \u003cp\u003eLike most islands around the world, the number of invasive plant species in the Yongxing Island (Paracel Islands) started rapidly increasing with human pressure in recent years. The main invasive plants in Yongxing Island are four Asteraceae species (\u003cem\u003eBidens pilosa\u003c/em\u003e, \u003cem\u003eSphagneticola trilobata\u003c/em\u003e, \u003cem\u003eTridax procumbens\u003c/em\u003e, and \u003cem\u003eWedelia biflora\u003c/em\u003e). Asteraceae have highly generalized floral traits, enabling them to utilize a wide variety of visitor species (Stouffer et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Emer et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Invasive Asteraceae \u003cem\u003eBidens pilosa\u003c/em\u003e, for instance, can attract ca. 60% of all the pollinators in the community (Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These four Asteraceae plant species are all super-generalists and attracted the majority of the pollinator species on the Yongxing Island (Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). However, the mechanisms that invasive Asteraceae plants integrated into the native Yongxing island ecosystem, and their specific effects on native plant pollination networks and fitness are little to known until now. Here, we constructed ten quantitative plant-pollinator interaction networks to explore invasive Asteraceae plants effects on native plant-pollinator interaction network structures and plant fitness on the Yongxing Island.\u003c/p\u003e"},{"header":"Material And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy sites and periods\u003c/h2\u003e \u003cp\u003eParacel Islands (15\u0026deg;46\u0026prime;-17\u0026deg;08\u0026prime;N, 110\u0026deg;11\u0026prime;-112\u0026deg;54\u0026prime;E) are a group of coral reefs in the tropical ocean on the continental slope of the South China Sea, and are located in the southeast of Hainan Island. The Yongxing Island (16\u0026deg;50.1\u0026prime;N, 112\u0026deg;19.8\u0026prime;E) has an area of 2.6 km\u003csup\u003e2\u003c/sup\u003e and is the largest island of this archipelago (for more details on its location, see Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e). In recent years, four Asteraceae species (\u003cem\u003eB. pilosa\u003c/em\u003e, \u003cem\u003eS. trilobata\u003c/em\u003e, \u003cem\u003eT. procumbens\u003c/em\u003e, and \u003cem\u003eW. biflora\u003c/em\u003e) have gradually started to invade this island due to human activity. We selected ten sites along an Asteraceae dominance gradient which defined as the proportion of Asteraceae flowers to the whole number of flowers, and the proportion values varied from 0\u0026ndash;56%. Ten 10 m x 10 m quadrats were located in each of the ten sites and at least 1000 m away from one another. The probability of movement of flower visitors among ten sites is extremely low because their limited average flying capacity on the island. Thus, each site could treat as an independent species assemblage. We collected the field data of flowering plants and their potential pollinators between 2 July and 30 August 2018. Plant species flowering patterns did not change during the two continuous months, and all visitor species were active for the whole duration of the study.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFloral Abundance\u003c/h3\u003e\n\u003cp\u003eWe assessed the floral abundance by recording the number of open flowering units for each plant species in the ten quadrats. The number flowers was counted within each quadrat for each flowering plant species, excluding wind-pollinated grasses. We defined flowering units as single flowers for most species, while for Asteraceae and Euphorbiaceae, the whole inflorescence was recorded as one flowering unit. Asteraceae invasion degree at each site was defined as the proportion of Asteraceae flowers in each quadrat. We calculated the proportion as the number of Asteraceae flowers divided by the entire number of open flowering units per quadrat.\u003c/p\u003e\n\u003ch3\u003ePollination Observation\u003c/h3\u003e\n\u003cp\u003ePollination observation was conducted on windless sunny days between 9:00 h and 16:00 h. Visitation rate was quantified for all the native and invasive Asteraceae plant species in each quadrat. Each site was observed for one day for each field observation round, and we conducted four rounds in total. The total observation time was about 25 hours per site. We recorded the visits to the flowers of each plant species during each 30 min observations. Only visits that visitor contacted with the reproductive organ (i.e., anther and/or stigma) of a flower for more than 2 s were recorded for each observation interval. If the same visitor individual return back to visit the same flower, such behavior was recorded as a new visit for the plant. All flower visitors found to be feeding on flowers were recorded, but ignoring their visitation efficacy. Opening flower numbers of each plant species in each site were counted before the pollinator observation. Pollinator visitation rate was measured as the average numbers of recorded visits/flower/hour during the observation periods. All native and invasive Asterace plant species and pollinator species in the Yongxing island community have been identified to the species level in our previous study (Wang et al., \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Thus, in this study, the visitation rate of each pollinator species to each native and invasive Asteraceae plant species could be both accurately recorded in the field.\u003c/p\u003e\n\u003ch3\u003ePollination Networks\u003c/h3\u003e\n\u003cp\u003eFor each site, we conducted one quantitative plant-pollinator network using pollinator species visitation frequencies to each native and invasive Asteraceae plant species as a surrogate of interaction strength. Metrics elucidating network structural properties were calculated to examine the changes of the network structure along the Asteraceae invasion gradient. Interaction evenness measured the frequency uniformity of network interactions. Linkage density measures the marginal weighted diversity of interactions of each species. Network-level specialization (H\u003csub\u003e2\u003c/sub\u003e\u0026prime;) describes to which degree observed interactions deviate from those expected for a given marginal amount of species. Weighted connectance measures the portion of realized interactions happening within the networks, increases with network generalization. Weighted nestedness measures the interaction degree of specialized species within the network, considering interaction frequencies. Nested contribution of Asteraceae and non-Asteraceae plant species were calculated for each site. Some inherent characteristics, for example, the number of interaction species (i.e. matrix size) and sampling intensity could both influence network metrics (Fr\u0026uuml;nd et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Thus, metric significance was estimated by comparison with the Patefield null model networks, which fixed the network size and marginal total, and randomly shuffling interactions. For each network-level metric, the 95% confidence interval from 1000 simulated values was assessed. If a metric value did not overlap with the confidence interval, then it was considered significant. All network-related metrics were calculated using the bipartite package in R 4.1.3.\u003c/p\u003e\n\u003ch3\u003ePollen Deposition On Stigma\u003c/h3\u003e\n\u003cp\u003eTo evaluate invasive Asteraceae effects on the pollen grains deposition of native plant species in the same community, we used three native plant species (\u003cem\u003eCanavalia maritima\u003c/em\u003e, \u003cem\u003eScaevola taccada\u003c/em\u003e, and \u003cem\u003eTribulus cistoides\u003c/em\u003e) that were present in more than three sites and quantified the number of conspecific, heterospecific, and Asteraceae pollen grains deposited on plant stigmas. \u003cem\u003eC. maritima\u003c/em\u003e has purple and restrictive flowers. \u003cem\u003eS. taccada\u003c/em\u003e has white and zygomorphic flowers with a spilt corolla tube ca. 18 mm in length. \u003cem\u003eT. cistoides\u003c/em\u003e has open, yellow, and actinomorphic flowers. Among the three native plant species, \u003cem\u003eT. cistoides\u003c/em\u003e has a similar flower shape and color compared with the invasive Asteraceae plant species. The flower shape of the four Asteraceae and three native plant species are shown in Figure S1. All three native plant species shared flower visitors with Asteraceae, and might strongly compete with Asteraceae. After observation, we collected 15\u0026ndash;20 stigmas for each native plant species per quadrat that contained these species. For three native plant species, stigmas from 150 flowers were gathered and stored separately in FAA solution (formalin, glacial acetic acid, and 70% ethanol in a 1: 1: 18 ratio) in clean microcentrifuge tubes. Furthermore, we collected 50\u0026ndash;55 stigmas for each Asteraceae plant species across the ten quadrats, and an overall total of 209 Asteraceae stigmas were stored.\u003c/p\u003e \u003cp\u003eIn the laboratory, each stigma was softened in 8 mol/l NaOH solution for 4 hours and placed on a clean slide. Pollen grains that dropped from the stigma into the solution were centrifuged and transferred with pipette from the bottom 50 \u0026micro;l of supernatant to another clean slide. For seven plant species, conspecific, heterospecific, and Asteraceae pollen grains on each slide were detected using a light microscope (BX41, Olympus) and identified by comparison to a field pollen reference library based on morphological characteristics such as shape and size. Furthermore, invasive Asteraceae plant pollen have special shape which clearly different from all other plant species, and thus can easily be identified, thus we have confidence in regarding the quantification of their pollen grains. We recorded the numbers of conspecific, heterospecific, and Asteraceae pollen grains for each stigma. The pollen g rains of four Asteraceae plant species were similar in shape, but differed in size; thus, their pollen grains could be distinguished under light microscope. We did not distinguish the species of other heterospecific pollen since it was not the focus of this study. The proportion of conspecific, heterospecific, and Asteraceae pollen grains was also calculated for three native and four Asteraceae plant species.\u003c/p\u003e\n\u003ch3\u003eStatistical Analyses\u003c/h3\u003e\n\u003cp\u003eTo determine flower visitor floral preferences along the Asteraceae invasion gradient, resource selection null model was used to detect whether the floral visitation rate of each plant species were higher or lower than expected based on their flower abundance by using the econullnetr package in R (Vaughan et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The resource selection null model assumes that the visitation rates of plant species in the community are proportional to their floral abundance.\u003c/p\u003e \u003cp\u003eGeneralized linear mixed models were conducted for each response to assess whether the Asteraceae invasion gradient influenced the Asteraceae and non-Asteraceae plants\u0026prime; nested contribution, and the interactions between species, which were higher or lower visitation rate than expected based on floral abundance. The models were run using a binomial error distribution with a logit link function for pollen proportion. To examine how network metrics changes along the Asteraceae invasion intensity, we used generalized linear mixed models to analyze Asteraceae proportion impacts on pollination network structure (interaction evenness, linkage density, network-level specialization, weighted connectance, and weighted nestedness). All models included Asteraceae flower proportion as fixed effect, and site as a random factor.\u003c/p\u003e \u003cp\u003eOne-way ANOVA was used to test for difference in the proportion of conspecific, heterospecific, and Asteraceae pollen grain deposition on stigma among four/three sites to evaluate Asteraceae invasion effects on the pollen deposition of three native plant species in the same community. We also used One-way ANOVA to compare the proportional differences in conspecific, heterospecific, and Asteraceae pollen grain deposition on stigmas in each Asteraceae plant species. All data were analyzed using the lme4 and bipartite packages in R 4.1.3.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eIn the ten sites, we sampled 37 plant species belonging to 21 plant families and 35 pollinator species. Lists of the plant and pollinator species are shown in supplementary table 1 and Table \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, respectively. The number of plant and pollinator species, interaction evenness, linkage density, network-level specialization, weighted connectance, and weighted nestedness per site are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Most pollinators were Hymenoptera (45.7%), followed by Lepidoptera (28.6%), Diptera (22.9%), and Passeriformes (2.9%).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe proportion of Asteraceae flowers and the values of network-level metrics for quantitative plant-pollinator networks in ten sites. Asterisks represents network metrics which are significant, i.e., do not overlap null model expectations (95% confidence interval).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSite (proportion of Asteraceae flowers)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePlant species number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePollinator species number\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eInteraction evenness\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLinkage density\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSpecialization (H\u003csub\u003e2\u003c/sub\u003e\u0026prime;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eWeighted connectance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eWeighted nestedness\u003c/p\u003e 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colname=\"c8\"\u003e \u003cp\u003e0.09\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3 (0.06)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.55\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.58\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.54\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.13\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.24\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4 (0.14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.52\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.25\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.39\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.11\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.47\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5 (0.17)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.65\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.31\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.63\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.13\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.20\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6 (0.21)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.44\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.41\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.42\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.11\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.27\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7 (0.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.61\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.45\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.44\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.15\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.51\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8 (0.33)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.49\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.02\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.52\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.13\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.66\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9 (0.45)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.53\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.97\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.51\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.13\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.31\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10 (0.56)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.48\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.24\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.55\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.15\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e0.73\u003csup\u003e*\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFive network-level quantitative metrics in ten sites, comparing observed values to the 95% confidence limits from the null model and including the standardized effect size (SES).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSite\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eInteraction evenness\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eLinkage density\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eSpecialization (H2\u0026prime;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003eWeighted connectance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003eWeighted nestedness\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSES\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSES\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSES\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSES\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eTest\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eSES\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e12.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-0.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLower\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eLower\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e-1.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e2.23\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e-0.14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e-1.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e7.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e-0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e2.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e-0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e7.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e-0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e7.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e-0.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e2.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e9.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e-0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e2.86\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e-0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHigher\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e \u003cp\u003e6.98\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eComparison Of Networks Using The Resource Selection Null Model\u003c/h3\u003e\n\u003cp\u003eWeighted nestedness values were higher than expected in nine sites, except in site three, while specialization values did not differ from expected values for all sites (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). None of the plant-pollinator links were weaker than expected based on flower abundance in all ten sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). For non-Asteraceae pollinator links, 28.7% \u0026plusmn; 4.0% were stronger than expected based on flower abundance. For Asteraceae pollinator interactions, 31.1% \u0026plusmn; 5.7% were stronger than expected. The Asteraceae flower proportion did not affect the stronger link proportion for either non-Asteraceae (df\u0026thinsp;=\u0026thinsp;8, t = -1.376, P\u0026thinsp;=\u0026thinsp;0.206) or Asteraceae (df\u0026thinsp;=\u0026thinsp;7, t = -1.158, P\u0026thinsp;=\u0026thinsp;0.285) plants (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eThe Impact Of Invasive Asteraceae On Pollination Network Structure\u003c/h3\u003e\n\u003cp\u003eBoth weighted connectance (df\u0026thinsp;=\u0026thinsp;8, t\u0026thinsp;=\u0026thinsp;2.697, P\u0026thinsp;=\u0026thinsp;0.027) and weighted nestedness (df\u0026thinsp;=\u0026thinsp;8, t\u0026thinsp;=\u0026thinsp;2.569, P\u0026thinsp;=\u0026thinsp;0.033) increased significantly with the proportion of Asteraceae increased (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e; Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Interaction evenness, linkage density, and specialization did not significantly change with the proportion of Asteraceae increased (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResults of the generalized linear mixed models used to test the effects of the proportion of Asteraceae flowers on five quantitative network-level metrics. The values heighted in bold are statistically significant based on likelihood ratio tests (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNetwork metric\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStd.Error\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003et\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInteraction evenness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.144\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.357\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.730\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLinkage density\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.111\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.367\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.723\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecialization (H\u003csub\u003e2\u003c/sub\u003e\u0026prime;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.193\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.723\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.490\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeighted connectance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.697\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e0.027\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWeighted nestedness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.292\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.569\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e0.033\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eComparison Of Nested Contribution Between Invasive Asteraceae And Non-asteraceae Plants\u003c/h3\u003e\n\u003cp\u003eInvasive Asteraceae plants were higher in nested contribution compared to native plants in most sites, even though differences were not always significant (Table S3, Figure S2). The pollination network nested contribution difference between Asteraceae and non-Asteraceae plants increased as the proportion of Asteraceae increased (df\u0026thinsp;=\u0026thinsp;7, t\u0026thinsp;=\u0026thinsp;2.61, P\u0026thinsp;=\u0026thinsp;0.035, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eThe Impact Of Invasive Asteraceae On Stigma Pollen Loads In Three Native Plant Species\u003c/h3\u003e\n\u003cp\u003eFor \u003cem\u003eC. maritima\u003c/em\u003e, we totally recorded 3838 pollen grains on 50 stigmas from three sites, 97.0% of which were conspecific, 2.8% of which were heterospecific, and 0.2% of which were Asteraceae pollen. The proportion of conspecific pollen grains on stigmas decreased while the proportion of heterospecific pollen grains increased significantly as Asteraceae invasion level increased (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResults of the generalized linear mixed models used to test the effects of Asteraceae on the proportion of conspecific pollen (CP), heterospecific pollen (HP) and Asteraceae pollen (AP) deposition on stigmas of co-flowering native species of C. maritime, S. taccada and T. cistoides separately. The values highlighted in bold are statistically significant based on likelihood ratio tests (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecies\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eResponse\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSum Sq\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMesn Sq\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003edf\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eP\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cem\u003eC. maritima\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of CP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e8.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e0.0007\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of HP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e0.006\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of AP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.247\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cem\u003eS. taccada\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of CP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e0.002\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of HP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.104\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of AP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e0.04\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e\u003cem\u003eT. cistoides\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of CP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e37.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of HP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.389\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProportion of AP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e23.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor \u003cem\u003eS. taccada\u003c/em\u003e, we totally recorded 10421 pollen grains on 52 stigmas from four sites, 98.7% of which were conspecific, 0.5% of which were heterospecific and 0.8% of which were Asteraceae pollen. As the Asteraceae invasion level increased, the conspecific pollen grain proportion on stigmas decreased, while the Asteraceae pollen grain proportion increased significantly (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor \u003cem\u003eT. cistoides\u003c/em\u003e, we totally recorded 8433 pollen grains on 50 stigmas from four sites, 45.1% of which were conspecific, 9.7% of which were heterospecific, and 45.2% of which were Asteraceae pollen. As the Asteraceae invasion level increased, the conspecific pollen grain proportion on stigmas decreased, while the Asteraceae pollen grain proportion increased significantly (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003ePollen Loads On Stigmas In Four Invasive Asteraceae Plants\u003c/h3\u003e\n\u003cp\u003eFor four Asteraceae plant species, namely \u003cem\u003eB. pilosa\u003c/em\u003e, \u003cem\u003eS. trilobata\u003c/em\u003e, \u003cem\u003eT. procumbens\u003c/em\u003e, and \u003cem\u003eW. biflora\u003c/em\u003e, we counted a total of 5207, 6577, 4183, and 5519 pollen grains on 53, 50, 53, and 53 stigmas, respectively, across ten sites (not all sites). A total of 99.5%, 95.5%, 99.6%, and 98.2% were conspecific, 0.2%, 2.8%, 0.1%, and 1.6% were heterospecific, and 0.3%, 1.8%, 0.3%, and 0.1% were other Asteraceae pollen grains, respectively. In all four Asteraceae plant species the conspecific pollen grain proportion was significantly higher compared to heterospecific and other Asteraceae pollen grains deposited on the stigmas (all P\u0026thinsp;\u0026lt;\u0026thinsp;0.001, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe plant-pollinator interaction network structures clearly changed as the Asteraceae invasion level increased. Both weighted connectance and weighted nestedness increased significantly as the proportion of Asteraceae increased. These results add significantly to our understanding of how plant-pollinator interaction network structures vary with the plant invasion gradient on oceanic island. Moreover, invasive Asteraceae plants had a higher nested contribution compared to native plants, and this difference increased as the Asteraceae proportion increased. This implied that invasive Asteraceae plants may help to shape pollination network structure. In all three native plant species the conspecific pollen grain proportion on stigmas decreased significantly as the Asteraceae invasion level increased. Also, in two native plant species the Asteraceae pollen grain proportion on the stigmas increased significantly as the Asteraceae invasion level increased. In all four Asteraceae invasive plant species the conspecific pollen grain proportion was significantly higher compared to heterospecific and other Asteraceae pollen grains deposited on the stigmas. These results provide insight into how invasive plants influence plant-pollinator interactions, as well as native plant pollen deposition on Oceanic Island. Generally, this study revealed that plant-pollinator interaction network structure changed as invasive plant intensity increased, thereby resulting in significant negative effects on native plant reproduction.\u003c/p\u003e \u003cp\u003eIn the Yongxing island community, invasive Asteraceae plants enhance a nested pattern and increase network connectance, but did not significantly affect other network parameters, such as interaction evenness, linkage density, and specialization as Asteraceae invasion level increased. This result supports previous findings that network connectance is positively related to invasive plant abundance (Stout and Casey \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In contrast, other research suggested that invasive plants had a low impact on plant-pollinator network structure (Traveset et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Super generalist pollinators can facilitate invasive plant integration into native pollination network, and support network structure by increasing network connectance and nestedness in invaded communities (Albrecht et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This could also be the case in our community where the super generalist pollinator \u003cem\u003eApis cerana\u003c/em\u003e visits most of the flowers on the Yongxing island and thus contributes to a large proportion of flora visits (Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2020c\u003c/span\u003e), even frequently visiting a bird pollinated plant species (Wang et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2020d\u003c/span\u003e), and may help to structure pollination networks. A new research suggested that invasive plant species interact with more generalist pollinator species, whereas specialist pollinators more severely depend on native plant species (Parra-Tabla and Arceo-G\u0026oacute;mez \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In our community, however, some other generalist pollinators, such as \u003cem\u003eBraunapis puangensis\u003c/em\u003e, \u003cem\u003eCeratina lieftincki\u003c/em\u003e, and \u003cem\u003eMicromeriella marginella\u003c/em\u003e, as well as specialized pollinators, such as butterflies and hawkmoths, also frequently visited Asteraceae plants in the generalized community (Wang et al. \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2020a\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2020b\u003c/span\u003e, Wang et al. \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which also increased pollination network nestedness and connectance and may lead to more generalist networks in the oceanic island community. Therefore, invasive Asteraceae plants act as super-generalists, thereby attracting most pollinator species and notably increasing network nestedness (Bartomeus et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Russo et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Network-level connectance and nestedness are usually used to describe plant-pollinator interaction network structures, which are useful and important topological metrics for representing the degree to which communities are reshaped in face of plant invasions (Campbell et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Our findings highlight the potential importance of super generalist pollinators and invasive Asteraceae species in structuring pollination networks in invaded oceanic island communities. The fact that network weighted connectance and nestedness increased with invasive Asteraceae abundance in our study suggests that invasive generalized plants could enhance oceanic island community stability and resilience.\u003c/p\u003e \u003cp\u003eThe nested contribution of invasive Asteraceae plants was higher compared to non-Asteraceae plants, and this difference increased as Asteraceae abundance increased. Our findings contrast with works in Oʻahu (Hawaiian Archipelago), the data of which showed that native and invasive plants contribute equally to nestedness in seed dispersal networks (Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Vizentin-Bugoni et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Our results support the findings of Stouffer et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), namely that networks where invasive plants are present are characterized by higher nestedness based on a global database of empirical pollination networks. Furthermore, similar findings have also been reported recently in urban green spaces, suggesting that exotic plant species contribute more to network nestedness than native plant species (Zaninotto et al. \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Nested pattern in plant-pollinator networks suggests a more stable community structure as functional redundancy is high, and thus more generalist species being able to interact with the partners of lost specialists (Th\u0026eacute;bault and Fontaine \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Thus, invasive Asteraceae may contribute more to increasing functional redundancy by increasing network nestedness, which is expected to enhance community stability, than non-Asteraceae plants. This suggests that invasive Asteraceae plants play a more important network stabilization role than native plants, and also provide additional resources for native pollinators in the Yongxing island community. In our study, the nested contribution differences between Asteraceae and non-Asteraceae plants increased as Asteraceae abundance increased, thereby implying its network importance. Network species importance is reported to be positively associated with plant abundance (Vizentin-Bugoni et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). If flowers of invasive plant species are open and unrestrictive which can attract a wide range of pollinator species, they may contribute more to increase network nestedness. It is well known that species which contribute more to network nestedness are also vital for the entire network\u0026rsquo;s persistence (Saavedra et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Previous work showed that invasive plant species tend to interact with specialist pollinators which also weakly contribute to network nestedness (Stouffer et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Similarly, in our community, the generalized Asteraceae plants not only interacted with generalized pollinators, such as bees (\u003cem\u003eApis cerana\u003c/em\u003e), but also frequently interacted with specialists, such as hoverflies (e.g., \u003cem\u003eAsarkina porcina\u003c/em\u003e) and butterflies (\u003cem\u003eZizina otis\u003c/em\u003e). Theoretical study has proposed that specialists are the most vulnerable to extinction, but as a weaker nestedness contributor can balance this consequence (Saavedra et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Therefore, invasive Asteraceae plants may have benefited the vulnerable specialist visitors on isolated oceanic islands.\u003c/p\u003e \u003cp\u003eInvasive Asteraceae pollen was detected on native plant species stigmas, supporting that heterospecific pollen deposition was also common in invaded communities (Johnson and Ashman \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). A meta-analysis of 76 studies showed that invasive plants both positively facilitate and negatively reduce native pollination (Charlebois and Sargent \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). For example, Parra-Tabla et al. (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) found that alien heterospecific pollen significantly reduces pollination success, for example, by affecting native species\u0026rsquo; pollen tube growth, in coastal communities, while Lopes et al. (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) found that heterospecific pollen deposition causes a higher reproductive success through increased conspecific pollen deposition. In our study, the conspecific pollen proportion on stigmas decreased significantly in \u003cem\u003eC. maritima\u003c/em\u003e, \u003cem\u003eS. taccada\u003c/em\u003e, and \u003cem\u003eT. cistoides\u003c/em\u003e, and the Asteraceae pollen grain proportion on stigmas increased significantly in \u003cem\u003eS. taccada\u003c/em\u003e and \u003cem\u003eT. cistoides\u003c/em\u003e with increasing Asteraceae invasion, indicating that invasive Asteraceae might negatively affect pollination service quality for native plant species. This effect is likely to be due to the high number of shared pollinators between invasive Asteraceae and native plants. Moreover, the Asteraceae pollen proportion on the stigmas of \u003cem\u003eT. cistoides\u003c/em\u003e was higher than the other two native species, indicating that invasive Asteraceae might have stronger negative effects on \u003cem\u003eT. cistoides\u003c/em\u003e. This may be explained by floral trait differences among three native plant species. \u003cem\u003eT. cistoides\u003c/em\u003e has yellow and radially symmetric flowers, and is very similar to \u003cem\u003eS. trilobata\u003c/em\u003e and \u003cem\u003eW. biflora\u003c/em\u003e. These similar floral traits (flower shape and color) between native and invasive plants can reinforce negative impacts of invasive plants on native plant species reproduction success (Morales and Traveset \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In contrast, \u003cem\u003eC. maritima\u003c/em\u003e and \u003cem\u003eS. taccada\u003c/em\u003e have bilaterally symmetrical, purple, and white flowers; thus, the Asteraceae pollen proportion on these stigmas was both less than 1%. This result was consistent with a recent research that showed that species with yellow flowers could receive more heterospecific pollen than species with purple flowers (Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Heterospecific pollen that from invasive plants can decrease fruit and seed set of plants to a greater degree than heterospecific pollen that from native plants (Arceo-G\u0026oacute;mez and Ashman \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Therefore, invasive Asteraceae plant species may indirectly and detrimentally affect native plant reproduction, especially for plants that share similar floral traits with them.\u003c/p\u003e \u003cp\u003eAlien species can easily invade native communities if they have greater capacity to donate, but avoid, heterospecific pollen compared to native plants (Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Our findings support this theory by revealing pollen load differences between invasive Asteraceae and native plants. Specifically, the invasive Asteraceae pollen deposited on the stigmas of the native plant \u003cem\u003eT. cistoides\u003c/em\u003e were as much as 45.2%. Similarly, in four invasive Asteraceae plant species, in excess of 95% of the pollen grains deposited on their stigmas were conspecific pollen. Furthermore, the conspecific pollen proportion on stigmas reached up to 99.5% and 99.6% in \u003cem\u003eB. pilosa\u003c/em\u003e and \u003cem\u003eT. procumbens\u003c/em\u003e, respectively. These results consistent with a recent research that invasive plant species are more frequently heterospecific pollen donors, and native plant species are more frequently heterospecific pollen recipients (Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Low heterospecific pollen loads in four Asteraceae plants suggested that avoidance of heterospecific pollen receipt may be a vital strategy determining whether they can successfully invade and integrate into native pollination networks on Yongxing Island. Overall, our results suggest that higher heterospecific pollen donation, along with a fairly low heterospecific pollen deposition on invasive Asteraceae plant stigmas may aid in their successful invasion of native communities. This highlights the essential for future researches to assess their importance and functional role, especially in heterospecific pollen transfer networks (Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eResearches have reported that plant-pollinator interaction networks had strong resistance to invasive plant species (Vil\u0026agrave; et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Parra-Tabla et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, our findings show that invasive plants can change pollination network structures and influence community robustness via increasing the network-level connectance and nestedness. Moreover, these structural network changes could enhance community stability, which seems beneficial for the whole system. On the other hand, our findings suggested that invasive plants may potentially affect native plant species reproduction, especially for plants that share their floral traits, by increasing heterospecific pollen deposition in the community. Invasive Asteraceae received few heterospecific pollen grains, which may be a strategy that helps them successfully invade native communities. To better understand the invasive plant species impacts on natural communities, it is necessary for integrative researches that simultaneously considered invasive species effects on pollination network structures, heterospecific pollen deposition, and native plant species reproduction. For example, a recent research suggested that heterospecific pollen transfer networks among plant species continue relatively constant regardless of plant invasion degree (Parra-Tabla et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, in order to more fully understand the ecological and evolutionary consequences of changes in pollination network structures, integrating information including all pollination process levels is important.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Tong zeng, Mingsong Wu for their worthy help in the field. We thank the logistical support on the Yongxing Island from Xisha Ocean observation and research station, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China. This study was supported by the National Natural Science Foundation of China (grant number 32271613, 32170232), the Natural Science Foundation of Guangzhou (grant number 202201010218), the National Key Research and Development Program of China (grant number 2021YFC3100405) and the Science and Technology Basic Works Program of Ministry of Science and Technology of China (grant number 2019FY202100).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors declare no conflict of interest and gave final approval for publication.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAizen, M. A., Morales, C. L., Morales, J. M. (2008) Invasive mutualists erode native pollination webs. \u003cem\u003ePLoS biology\u003c/em\u003e, 6(2), e31.\u003c/li\u003e\n\u003cli\u003eAlbrecht, M., Padr\u0026oacute;n, B., Bartomeus, I., Traveset, A. 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(2023) Native and exotic plants play different roles in urban pollination networks across seasons. \u003cem\u003eOecologia\u003c/em\u003e, 1-12.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Plant-pollinator interactions, invasive Asteraceae plants, network structure, nested contribution, pollen deposition, invasive strategy","lastPublishedDoi":"10.21203/rs.3.rs-2546012/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2546012/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eInvasive plant species severely threaten natural plant communities around the world, especially for islands. As introduction rates rise, novel species interactions appear within ecosystems. Studies that focus on invasive plant impacts on native plants, especially on native communities, remain largely unexplored and their conclusions are mixed. We constructed ten quantitative plant-pollinator interaction networks and calculated five network-level structure metrics (interaction evenness, linkage density, specialization, weighted connectance, and weighted nestedness) along an Asteraceae invasion gradient in the Yongxing Island community. We calculated the species-level nested contribution of each plant species in each network, and compared the nested contribution differences between invasive Asteraceae and non-Asteraceae species. Stigmas of three native and four invasive Asteraceae species were collected, and their pollen grains were identified. We analyzed invasive Asteraceae species impacts on native pollination network structure and native plant fitness. Both weighted nestedness and weighted connectance increased significantly as invasive Asteraceae became increasingly dominant. Invasive Asteraceae plants had higher nested contribution compared to native plants in most sites, and their nested contribution difference increased as the Asteraceae proportion increased. Furthermore, in native plant species, the proportion of conspecific pollen grains on stigmas decreased significantly, while the proportion of Asteraceae pollen grains on stigmas increased significantly with Asteraceae invasion level increased. For four invasive Asteraceae species, the proportion of conspecific pollen grains was significantly higher than heterospecific and other Asteraceae pollen grains on the stigmas. These results significantly add to our understanding of how the structure of plant-pollinator interaction networks changes concomitantly with plant invasion intensity. Invasive Asteraceae increase community stability and persistence, and negatively affect native plant fitness by influencing heterospecific pollen deposition on stigmas as invasion level increases. Invasive plants may greatly shape network structure and maintain community stability in oceanic island systems. Heterospecific pollen avoidance may be crucial mechanism facilitating Asteraceae invasion success within native communities, together with their \u0026lsquo;integration\u0026rsquo;, into plant-pollinator interactions on the Yongxing Island.\u003c/p\u003e","manuscriptTitle":"Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-02-10 22:29:20","doi":"10.21203/rs.3.rs-2546012/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2023-02-08T16:57:22+00:00","index":0,"fulltext":""},{"type":"editorInvited","content":"Biological Invasions","date":"2023-02-05T16:01:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-02-03T10:22:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Biological Invasions","date":"2023-02-03T04:17:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"biological-invasions","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"binv","sideBox":"Learn more about [Biological Invasions](https://www.springer.com/journal/10530)","snPcode":"10530","submissionUrl":"https://submission.nature.com/new-submission/10530/3","title":"Biological Invasions","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8b7dd913-b54e-4d25-90bf-1fda49d8b1a2","owner":[],"postedDate":"February 10th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-10-16T21:51:58+00:00","versionOfRecord":{"articleIdentity":"rs-2546012","link":"https://doi.org/10.1007/s10530-023-03129-w","journal":{"identity":"biological-invasions","isVorOnly":false,"title":"Biological Invasions"},"publishedOn":"2023-07-18 21:42:45","publishedOnDateReadable":"July 18th, 2023"},"versionCreatedAt":"2023-02-10 22:29:20","video":"","vorDoi":"10.1007/s10530-023-03129-w","vorDoiUrl":"https://doi.org/10.1007/s10530-023-03129-w","workflowStages":[]},"version":"v1","identity":"rs-2546012","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2546012","identity":"rs-2546012","version":["v1"]},"buildId":"cBFmMYwuxLRRLfASyISRj","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}