Insect Herbivory Along Elevational Gradients in Mediterranean-Type Climate Ecosystems: A Meta–Analytical Perspective

Insect Herbivory Along Elevational Gradients in Mediterranean-Type Climate Ecosystems: A Meta–Analytical Perspective | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 27 May 2025 V1 Latest version Share on Insect Herbivory Along Elevational Gradients in Mediterranean-Type Climate Ecosystems: A Meta–Analytical Perspective Authors : Scott Altmann 0000-0002-1792-6163 [email protected] and Ana Laura Pietrantuono Authors Info & Affiliations https://doi.org/10.22541/au.174836006.66889361/v1 343 views 141 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The effect of elevation on insect herbivory has been a central topic in ecological research for decades. A key question is how insect herbivory varies along elevational gradients and the mechanisms driving these patterns. Recent meta-analyses have examined the relationship of elevation and insect herbivory globally and for tropical, polar and temperate climate zones. However, there is a lack of meta-analysis research focused on smaller-scale climate zones. Mediterranean-type climate (MTC) ecosystems are of particular importance since they constitute biodiversity hotspots and are threatened by anthropogenic forces including climate change which is having a disproportionate effect on these regions. Thus, understanding patterns of insect damage in these systems is important to both basic and applied science. We conducted a meta-analysis to assess the overall relationship of altitude and insect herbivore damage in MTC ecosystems considering the moderators damage type (leaf, seed, and borer); plant habit (woody and non-woody); elevation range (small vs. large); sampling period (< 2010 and 2010 ̵̶ 2025); taxonomic order (Fagales and non-Fagales), and leaf longevity (deciduous, semi-deciduous, evergreen). For overall herbivory and all but one moderator, we found no significant effects of elevation on insect damage in MTC ecosystems. For the 2010 ̵̶ 2025 sampling period moderator, we found a positive relationship of insect herbivory and altitude. A posteriori analyses with the 2010 ̵̶ 2025 sampling period group indicated positive relationships of elevation and herbivory in terms of leaf and seed damage; woody plants; and small elevation range. We point to climate change and the particularly hot and dry conditions in MTC ecosystems to explain results for recent sampling period. Abiotic conditions may be limiting to insects at lower elevations resulting in a range shift to higher elevations. Further research is necessary to validate these findings and to elucidate the underlying mechanisms. ABSTRACT The effect of elevation on insect herbivory has been a central topic in ecological research for decades. A key question is how insect herbivory varies along elevational gradients and the mechanisms driving these patterns. Recent meta-analyses have examined the relationship of elevation and insect herbivory globally and for tropical, polar and temperate climate zones. However, there is a lack of meta-analysis research focused on smaller-scale climate zones. Mediterranean-type climate (MTC) ecosystems are of particular importance since they constitute biodiversity hotspots and are threatened by anthropogenic forces including climate change which is having a disproportionate effect on these regions. Thus, understanding patterns of insect damage in these systems is important to both basic and applied science. We conducted a meta-analysis to assess the overall relationship of altitude and insect herbivore damage in MTC ecosystems considering the moderators damage type (leaf, seed, and borer); plant habit (woody and non-woody); elevation range (small vs. large); sampling period (< 2010 and 2010 ̵̶ 2025); taxonomic order (Fagales and non-Fagales), and leaf longevity (deciduous, semi-deciduous, evergreen). For overall herbivory and all but one moderator, we found no significant effects of elevation on insect damage in MTC ecosystems. For the 2010 ̵̶ 2025 sampling period moderator, we found a positive relationship of insect herbivory and altitude. A posteriori analyses with the 2010 ̵̶ 2025 sampling period group indicated positive relationships of elevation and herbivory in terms of leaf and seed damage; woody plants; and small elevation range. We point to climate change and the particularly hot and dry conditions in MTC ecosystems to explain results for recent sampling period. Abiotic conditions may be limiting to insects at lower elevations resulting in a range shift to higher elevations. Further research is necessary to validate these findings and to elucidate the underlying mechanisms. KEYWORDS Insect herbivory, Mediterranean-type climate, leaf damage, seed predation, borer damage, climate change INTRODUCTION Understanding the distribution of organisms and drivers of that distribution (abiotic and biotic) in time and space is the central goal of the field of ecology (e.g., MacArthur 1984; Agrawal et al. 2007). Understanding these interactions in the context of specific environments is important to this goal and mountain environments are no exception and have been studied as part of basic and applied ecology. Elevational gradients in a geographic area (local or regional) make up environmental clines whereby abiotic and biotic conditions vary to a lesser or greater degree (e.g., Hodkinson 2005; Abdala-Roberts et al. 2016). Because these conditions include temperature and precipitation, mountainous clines are being studied to better understand the effect of climate change on organisms and their interactions. Untangling the complex interactions of abiotic and biotic variables driving organism distribution across environmental gradients is critical to a fundamental understanding of ecosystem structure and function including organism interaction and evolution (e.g., Dobzhansky et al. 1950; MacArthur 1984) and also anthropogenic change (e.g., Parmesan et al. 2006). Abiotic variables such as temperature, humidity, wind, and UV radiation vary across altitudinal gradients and their effect on organisms like insects can be examined across a relatively small geographic area. Temperature decreases approximately 6.0° C for every 1000 m increase in altitude (Dillon et al. 2006) and has been hypothesized and shown to be a major driver of insect herbivore presence and damage across altitudinal gradients (e.g., Hódar and Zamora 2004; Abdala-Roberts et al. 2016; Birkemoe et al. 2016) although exceptions exist (see Leckey et al. 2014). Temperature can directly influence insect abundance and damage by affecting insect fitness (e.g., Hodkinson 2005; Johnson et al. 2023) and indirectly by affecting insect host plants (e.g., insect defenses; Abdala-Roberts et al. 2016; Valdés‑Correcher et al. 2025) and predator abundance (Straw et al. 2009). Depending on the elevational gradient, plant species and communities may be similar across the gradient, or different, for example in the case of a lower elevation dry scrubland and a higher elevation wet woodland. An understanding of the interactions between abiotic and biotic variables driving insect herbivory across elevational gradients remains a challenging and underdeveloped area of research. A widely held hypothesis posits that abiotic conditions (e.g., temperature) are more favorable to insects and their host plants at lower elevations and therefore insect abundances and herbivory will be higher there (e.g., Pellissier et al. 2012). Higher temperatures, lower UV radiation, less wind, and other abiotic variables at lower elevations may have a direct and positive effect on insect fitness including reproduction and survival (Hodkinson 2005). In terms of host plants, better conditions at lower altitudes can result in higher growth rates and lower herbivore defenses (a “trade-off”) which also positively impacts insect populations (Coley 1983; Coley et al. 1985). Research supports the idea that a trade-off exists of plant growth and defenses, and that this trade-off drives insect damage in plants (Endara and Coley 2011). However, empirical studies show mixed results of the relationship of insect herbivory and elevation. Some research has found an increase in herbivory with altitude while other research has found a decrease or a hump-like pattern where damage is greatest at mid-altitude (Rasmann et al. 2014). Two recent meta-analyses included an assessment of insect herbivory with altitude at a global scale and for dominant climate types (temperate, tropical, and polar). One of the analyses found no relationship of invertebrate folivory with altitude (Galman et al. 2018) whereas the other found a negative relationship (Zvereva and Kozlov 2022). Both studies reported globally a decline in insect folivory (leaf herbivory) with altitude for woody plants, which are often keystone species of ecosystems. Nevertheless, long-term patterns of insect herbivory and altitude may not reflect current trends due to anthropogenic impacts like climate change, which has driven shifts in insect distribution and altered plant – insect interactions. Understanding how rising temperatures and altered precipitation patterns affect insect herbivory across altitudinal gradients is critical for predicting the ecological consequences of climate change (Parmesan 2006). Currently, basic and applied research is limited on the relationship of insect herbivory and altitude in Mediterranean-type climate (MTC) ecosystems despite their known conservation value and anthropogenic threats to them. Mediterranean-type climate ecosystems are located approximately from 30° to 45° north and south latitude, cover less than 5% of the Earth’s land surface, and include areas of the Mediterranean Basin (Europe), western United States, southern Australia, central Chile and Argentina, and southwestern South Africa. These ecosystems are climatically characterized by hot or warm summers with a dry season of 1 to 6 months and mild rainy winters. The Mediterranean biome is an international conservation priority since it makes up five biodiversity “hotspots” including the “California Floristic Province” and the “Chilean Winter Rainfall Valdivian Forests” (Myers et al. 2000). Mediterranean-type climate ecosystems are threatened and are subject to fragmentation and disturbance from natural forces and anthropogenic forces including climate change, urbanization, agriculture, exotic plantations, mining, and grazing (Samways 1998; Myers et al. 2000; Paine and Lieutier 2016). In recent years, reports of dieback and decline associated with climate change has been reported in Mediterranean forests and has been associated with insect outbreaks (Paine and Lieutier 2016). In addition to promoting basic science, an understanding of insect herbivory along elevational gradients in MTC ecosystems is important to understanding the effects of climate change on organisms and their interactions in these and other environments. Recent data demonstrate trends of higher temperatures and drier conditions in MTC including the Mediterranean Basin (Deitch et al., 2017) and central Chile (Boisier et al. 2018; Garreaud et al. 2020), and warmer and drier conditions are projected to increase for these areas in the future (Tarín-Carrasco et al. 2024). As ectothermic organisms, insect survival and development are highly sensitive to temperature (Bale et al. 2002) and in MTC extreme temperatures can be lethal to insects at low elevations (Lieutier and Paine 2016). While acclimation or evolution is always an option with changing climatic conditions (Deutsch et al. 2008), migration is also an option and altitudinal range shifts (contraction or expansion) of insect groups (Parmesan 2006) have been observed in Mediterranean ecosystems (e.g., Battisti et al. 2006, Robinet et al. 2007). Beyond direct temperature effects, climate change can indirectly affect insect populations via changes in host plant quality and interaction with other organisms including natural enemies. Over time, this herbivory pressure could result in a decline or mass mortality of keystone species such oaks (Fagales), which play a central role in many MTC ecosystems (Paine and Lieutier 2016). For example, severe damage from leaf herbivores has been reported in Mediterranean forests including in Chile ( Paritsis et al. 2011) and Italy (Bussotti et al. 2024) and beetle engraver damage has been widely reported in the forests of California (Larvie et al. 2019). In this meta-analysis study, we examined the intensity of insect herbivory along elevational gradients in MTC ecosystems. We had noted some studies where higher insect herbivory and abundance were observed at higher elevations in MTC systems (e.g., Abdala-Roberts et al. 2016; Domocol 2019; Moraiti et al. 2019). This raised the question of whether the warm and dry conditions in MTC ecosystems impact insect abundance and damage at lower altitudes where temperatures and aridity would generally be highest. Baseline temperatures and aridity in the summer months at lower elevations may be high enough in MTC ecosystems to negatively impact insect fitness resulting in lower insect damage and abundance. Additionally, we questioned whether hotter and drier conditions associated with climate change in recent times may be contributing to any patterns we observed. The literature search for the meta-analysis included major insect damage types observed in MTC ecosystems: damage from leaf herbivores (folivory); seed predation (consumption or removal); and bark and wood borer damage. We considered damage from all different plant scales (i.e., leaf to whole plant) and the habits herb, shrub, and tree. We asked the following research questions: 1. Does overall insect herbivore damage vary with elevation? 2. Does insect leaf damage, seed predation, or borer damage vary with elevation? 3. Does insect herbivore damage vary with altitude based on plant habit (trees/shrubs (woody) vs. herbaceous/perennial (non-woody)? 4. Does insect herbivore damage vary between large and small elevation ranges? 5. In the last 15 years (2010 ̵̶ 2025), corresponding with a significant uptrend in temperature and drought from climate change in MTC ecosystems, did overall insect herbivore damage vary with altitude? 6. Does overall insect herbivore damage vary with altitude based on the Fagales taxonomic order, species of which are often keystone in MTC ecosystems? MATERIALS AND METHODS Literature Search We conducted several literature searches between January 2024 and April 2025 using Google Scholar to identify papers with data on insect herbivory and altitude within MTC ecosystems. The literature search focused on three classes of insect herbivory important to these areas: 1) leaf damage, 2) seed predation (damage or removal), and 3) borer damage including wood and bark damage. We searched for publications using combinations of the following keywords: ‘insect’, ‘Mediterranean’; ‘leaf herbivory’, ‘insect herbivory’, ‘leaf damage’, ‘elevation*’, ‘altitud*’, ‘seed*’, ‘leave*’, ‘seed consumption’, ‘seed predation’, ‘myrmecochory’, ‘ants’, ‘borer*’, ‘entry holes’, ‘exit holes’, ‘channeling insect*’. We included grey literature in the form of university theses. We assessed the potential for a paper to have relevant data based on the title and abstract in all cases and the main text in many cases (> 40%). We acknowledge that some relevant publication data may have been left out of our meta-analysis for several reasons: 1) the terms used in the search were different than those used in the paper, 2) the potential for relevant data from the title or abstract was missed, 3) a paper had relevant data but was lacking standard deviations or sample sizes; in this case we attempted to contact the authors if the paper was recent, but this wasn’t always successful 4) book sources were less vigorously reviewed since we generally did not discover relevant data this way, 5) only publications in English or Spanish were considered. We did not contact authors for raw data because of the practicality of this approach and legal rights concerning data. In sum, the literature search we conducted was “comprehensive and representative but not exhaustive” (Lindroth 2012). not-yet-known not-yet-known not-yet-known unknown Selection Criteria The data on insect herbivory in terms of elevational gradients in MTC ecosystems were highly variable in terms of geographic distribution. Although abiotic and biotic conditions change across geographic gradients, we assumed that conditions remained relatively similar across smaller gradients which we defined as a 200 x 200 km area. As discussed below, data collected within this geographic area corresponded with one “effect size” or case. We did not include data from a study where the altitudinal gradient was ≤ 20 m since we assumed random variability over such a short gradient. The type of insect damage varied across studies which led us to combine damage types into broad categories. The first damage category “leaf damage” made up folivory damage and would have included herbivory from leaf chewers (cutters), skeletonizers, miners, gallers, and sap-suckers. In several cases, damage was reported as “leaf damage” without specifying the exact damage type. The second damage category “seed predation” comprised herbivory where seeds were damaged (e.g., beetle consumption) or removed (e.g., ant myrmecochory). The third damage category “ borer damage” included herbivory from insect groups (e.g., beetles) that channel within woody layers (e.g., cambium) of a tree or shrub. We did not consider insect abundance data. However, we did include data where the presence of one or more larva(e) in a seed was equal to one predated seed; and in one of these cases there was a minimal presence (< 1 %) of mites (Arachnid sp.). We also included one study in which caterpillar silk tent length was included as a proxy for damage which we classified as leaf damage. From the literature search, we found data fulfilling our selection criteria in 32 publications covering 6 geographic areas including Africa, North America, Mediterranean Basin (Europe), Middle East, Oceania, and South America and 15 countries (Fig. 1). The geographic area with the most data coverage was the Mediterranean Basin (Europe; 15 publications) and the country with the most coverage was Spain (9 publications). The geographic area with the fewest number of publications was Oceania (1) for which there was one publication for Australia. Of the 32 publications 37.5 % (12) assessed leaf damage; 37.5 % (12) assessed seed predation; and 26.0 % (8) assessed borer damage (Table 1). Climate classification We used the recent climate classification of Beck et al. (2023) to define the geographic areas with MTC. The MTC has been typically characterized as hot and dry in the summer and wet and cool in the winter. Based on this definition, we assessed two climate classifications that most closely align with this general characterization and that correspond with areas typically classified as Mediterranean climate: 1) Csa : temperate, dry summer, hot summer, and 2) Csb : temperate, dry summer, warm summer. The Csa and Csb geographic areas of Beck et al. (2023) are located mainly in the Mediterranean Basin of Europe (e.g., southern Spain); the western United States (e.g., California); the southern cone of South America (e.g., central Chile); western South Africa; and southern Australia. Notably, the classification includes smaller areas not typically associated with MTC for example areas of Mexico and Ethiopia. The climate classification map of Beck et al. (2023) was used with ARCGIS Pro to assess whether the study area was within a Csa or Csb climate. In a few cases, the study area corresponded largely with either a Csa or Csb area but a few sampling points (< 10%) either bordered or were within another climate type. Data analysis Meta-analysis Comprehensive Meta-Analysis (CMA) V.4 (2022) software was used to analyze all data. Data were extracted from selected papers from the text, tables, and digital repositories (e.g., Dryad) and from figures using the online application PlotDigitizer. The CMA software calculates the effect size for data presented in different formats. We generally followed the meta-analysis criteria of Zvereva and Kozlov (2022) whose recent meta-analysis research assessed insect herbivory in terms of elevation at a global scale. For estimation of each effect size (case) we used two methods: 1) when data from two or three sites were reported, we used the difference in herbivory the lowest and highest elevation sites, and 2) when data from > 3 sites were reported, the correlation among sites. For data corresponding with two or three altitudes, we used the independent means with standard deviations and sample sizes or the t-test value with sample sizes. For data from > 3 sites, we first used the Pearson correlation and then applied Fisher’s-Z statistic for data homogeneity. We used the standardized mean difference, in this case the Hedge’s g calculation (Gurevitch and Hedges 1976), to estimate all effect sizes (Zvereva and Kozlov 2022). Low elevation herbivory was considered as the ‘control group’ and ‘high elevation’ herbivory as the ‘experimental group’. As such, a positive effect size means that herbivory increased with altitude while a negative effect size means the opposite. Data collection methods and presentation varied greatly and therefore relevant data were treated on a case-by-case basis. Most effect sizes were calculated based on herbivory measurement at one time for one plant species. In a few cases, data collection in a study resulted in different herbivory damage types, host species, or sampling times. Protocols were developed to treat these cases to reduce the potential for auto-replication (pseudoreplication). When data collection was conducted on a few dates, data from the most recent date were used. An exception was made for a long time-series data set in which case we averaged means, calculated the standard deviation, and used the sample size corresponding with one sampling date. In cases where different types of damage were reported, we used the most important one. So that the meta-analysis reflected a wide range of host species, in cases where herbivory in several species were measured, we generated a “composite” effect size across species (Borenstein et al. 2009). We assumed a degree of independence among species at a site which was supported by the fact that effect size sign (negative or positive) at a site often varied among species. In cases where sampling was conducted across a wide geographic area ( > 200 x 200 km area), we generated two or more effect sizes corresponding with different geographic areas. In two cases, we used community level data (across species) that were summarized in the study. In one case, seed predation data were collected in relation to seed placement under different shrub species and open areas; for this study, we only used the open area data. We avoided data for which more complex statistical calculations were required to generate means and standard deviations. We first tested the effect of elevation on insect herbivory using all estimated effect sizes across all studies. A fixed effects model was applied to combine cases within a subgroup (“composite” effect), and a random effect model was used to combine cases for the overall effect. We assumed the study-to-study variance (tau squared) to be the same for all subgroups; variance was computed within subgroups and then pooled across subgroups (Borenstein et al. 2009). We tested the moderators using random effects models: 1) damage type (leaf damage, seed predation, and borer damage) 2) habit ([tree/shrub (woody) and herbaceous/perennial (non-woody)] 3) elevational range (large and small) 4) sampling period (< 2010 and 2010 ̵̶ 2025), and 5) taxonomic order (Fagales and non-Fagales). We also tested the moderators separately as individual groups using random effects modeling. For the elevation range analysis, we were interested in whether a difference in herbivory with altitude would be based on a larger or smaller elevational range. We defined data in terms of whether they were collected from 0 ̵̶ 1499 masl and also at ≥ 1500 masl (large range) vs. data that were not collected within those parameters (small range). For the sampling period moderator, there was one case in which data were collected at the end of 2009 and the start of 2010; we classified the study in the < 2010 sampling period group to increase overall representation in that group. Finally, we conducted a posteriori tests for the 2010 ̵̶ 2025 sampling period group in using the different moderators. We also tested a posteriori the effect of leaf longevity (deciduous, semi-deciduous, evergreen) using the complete data set. We did not test this moderator for the 2010 ̵̶ 2025 sampling period group since sample sizes were too small for proper analysis. Data sensitivity and publication bias We employed two techniques to assess data sensitivity and publication bias. For the sensitivity analysis we used the “one study removed” technique in the CMA software to assess whether any one study had a disproportionate effect on the overall effect size. Thus, the effect size and probability value across studies are calculated in terms of the removal of each individual study. If it is found that the removal of any one study changes the overall effect size considerably or the probability value, then the study is an outlier and should be dealt with. We used the Duval and Tweedie’s “fill and trim” test in CMA to check for publication bias. The test evaluates whether smaller studies (low sample size studies) are biasing the analysis. It operates on the premise that smaller studies without statistically significant results are less likely to be published. The technique imputes smaller studies within a funnel diagram showing the mean effect size on the x axis and the standard error on the y axis. Imputed values are place in the funnel diagram in the area where there is an underrepresentation of smaller studies and a new “adjusted” effect size is calculated (Borenstein et al. 2009). Overall and by damage type Data extracted from the papers resulted in 42 effect sizes cases corresponding with 16 leaf damage cases, 16 seed predation cases, and 10 borer damage cases. The elevational gradient across studies ranged from 0 ̵̶ 2100 masl. The elevational range for leaf damage was 0 ̵̶ 2100 masl; the range for seed predation was 7 ̵̶ 1950 masl; and the range for borer damage was 20 ̵̶ 1200 masl. Overall, there were 20 cases of an increase in insect herbivory with altitude, 21 cases of a decrease in herbivory with altitude, and 1 case of neither an increase nor decrease. Using all of the data, the mean effect size was negative but was not significantly different than zero (g = 0.103, SE = 0.121, 95% CI = - 0.133 ̵̶ 0.339, n= 42, p = 0.39) indicating there is no evidence that insect herbivore damage either increases or decreases with altitude in MTC ecosystems. There was no significant effect of damage type (leaf, seed, borer) on insect herbivory with altitude when modeled or when damage types were analyzed separately as groups (Fig 2; Table 2). The Q statistic for heterogeneity for the entire data set was 170 (df = 41, p < 0.001) indicating that the true effect size is not the same in all the studies. The I-squared was 76% indicating that 76% of the data reflects variance in true effects and that the remainder (24%) is sampling error. The sensitivity test using the one study removed technique indicated no substantial change in either the Hedge’s g or p-value with the removal of any one effect size. We tested for publication bias using Duval and Tweedie’s trim and fill test for publication bias. The test indicated an adjustment of seven studies to the right of the mean. With the imputed values, Hedge’s g showed a positive increase to 0.254 which was a difference of 0.151 relative to the unadjusted effect size (95% CI: 0.026 ̵̶ 0.481; Fig. 3). Habit, elevation range, sampling period, taxonomic order, and leaf longevity moderators We found no significant result of the effect of habit (tree/shrub [woody] and herbaceous/perennial [non-woody]) on insect herbivory with altitude and no significant results were observed when habit was analyzed based on separate groups. Because of the low number of effect sizes for the non-woody species group (n = 2), the results for this habit should be disregarded. For the elevation range moderator (large and small), we found no significant result when modeled and no significant results when the analysis was run based on the two groups. Finally, we found no significant results for either taxonomic order (Fagales and non-Fagales) or leaf longevity (deciduous, semi-deciduous, evergreen) when moderators were modeled or when they were analyzed based on separate groups (Table 2). For the sampling period moderator (< 2010 and 2010 – 2025), we observed a significant positive relationship of insect herbivory and altitude. A significant result was also found when we analyzed the groups separately for the 2010 ̵̶ 2025 sampling period (g = 0.370, SE = 0.132, 95% CI = 0.109 ̵̶ 0.628, n = 27, p = 0.005) but not for the < 2010 sampling period (g = - 0.340, SE = 0.181, 95% CI = - 0.696 ̵̶ 0.015, n = 15, p = 0.06). These results indicate from the year 2010 onwards, there was a positive trend of insect herbivory with altitude (Fig. 4). Sampling period moderator We ran additional a posteriori analyses with the 2010 ̵̶ 2025 sampling period group. For this group, the one study removed sensitivity test indicated no substantial change in either Hedge’s g or p-value with the removal of any one effect size. Duval and Tweedie’s trim and fill test adjusted for publication bias with eight imputed studies to the right of the mean resulting in a moderate positive increase of Hedge’s g from the observed value of 0.363 to the imputed value of 0.622 (95% CI: 0.360 ̵̶ 0.884) which was a 0.259 increase. For this group, we found no significant result when we modeled damage type (Table 3); however, considering the damage type groups individually, there was a positive relationship of herbivory and altitude for the groups leaf damage (g = 0.460, SE = 0.187, 95% CI = 0.093 ̵̶ 0.827, n = 12, p = 0.01) and seed predation (g = 0.618, SE = 0.224, 95% CI = 0.179 ̵̶ 1.057, n = 8, p = 0.006; Fig. 5) while no significant result was found for borer damage. The moderator habit had no effect on insect herbivory and elevation when modeled; however, considering the separate groups, we found a positive result for the tree/shrub (woody) group (g = 0.309, SE = 0.134, 95% CI = 0.048 ̵̶ 0.571, n =25, p = 0.02). There was only one case of herbaceous/perennial (non-woody) insect herbivory and therefore the results for that group were disregarded. For the elevation range moderator, we found no significant relationship when this variable was modeled. However, considering analysis of the separate groups, we found a positive significant result for the small elevation range group (g = 0.360, SE = 0.146, 95% CI = 0.074 – 0.647, n = 23, p = 0.01; Fig. 6). For the moderator taxonomic order, we found no significant relationship when modeled. In contrast, separate group analysis showed a significant positive result for the non-Fagales group (g = 0.588, SE = 0.245, 95% CI = 0.108 ̵̶ 1.069, n = 8, p = 0.02). DISCUSSION Comparison of main results with other research Our meta-analysis revealed no significant relationship between insect herbivory and altitude in MTC ecosystems regardless of herbivory type. In contrast, a global meta-analysis of these variables by Zvereva & Kozlov (2022) indicated a significant negative relationship whereas results of another meta-analysis of these variables by Galman et al. (2018) aligned with our findings. Our findings of no relationship between seed predation and altitude are consistent with those of the Zvereva and Kozlov (2022). Similarly, we found no significant relationship between borer damage and altitude, and to our knowledge, this is the first study to investigate these variables at a broad climatic scale. For research assessing the effect of elevation on insect herbivory, it is critical to assess results in terms of the elevation range and climate system. The elevation range of our meta-analysis was 0 to 2100 masl which is comparable to the elevation range of 0 to 2755 masl for the Galman et al. (2018) meta-analysis. In contrast, the elevation range of the Zvereva and Kozlov (2022) meta-analysis was much wider ranging from -27 to 4640 masl. In both our study and that of Galman et al. (2018) abiotic conditions (e.g., temperature, wind speed) at higher altitudes would have been less severe for insects compared with the abiotic conditions at higher altitudes of studies in the Zvereva and Kozlov (2022) meta-analysis. Thus, it is no surprise that the Zvereva and Kozlov (2022) meta-analysis ̵̶ covering a much wider altitudinal range ̵̶ evidenced a significant decrease in insect herbivory with altitude since insects would be less tolerant to the harsher abiotic conditions found at the higher altitudes. Furthermore, our data come exclusively from the relatively mild MTC ecosystem, whereas the other meta-analyses included cooler climates (polar, temperate) ̵̶ thus abiotic conditions at higher altitudes would have been less harsh for our meta-analysis. The climate system in which insect herbivory is assessed is important since abiotic conditions of either a cooler or warmer climate system may have conditions along the gradient which are intolerable to insects but at notably different elevations (e.g., tolerance at 2,800 masl in a cooler climate vs. tolerance at 2,800 in a warmer climate). In mountainous areas within MTC ecosystems, abiotic conditions at higher elevations may not reach levels that are seriously limiting to insects. It is important to emphasize that in MTC ecosystems, at a certain elevation (e.g., > 3000 masl), the climate will transition into another climate type (e.g., sub-alpine) at which point insect herbivore indices are not pertinent to MTC ecosystems. While this distinction may seem obvious, to improve understanding of patterns of insect herbivory along altitudinal gradients, it is important to identify the climate type along the gradient in which the herbivory is being assessed. The nature of the meta-analysis data There are important caveats to consider in light of our findings. Both overall and group data showed high heterogeneity (variability) evidenced by large confidence intervals and high Q values. In general, this heterogeneity indicates that the difference in insect herbivory between low and high altitude at any one site may vary from the mean difference. The factors responsible for this variability are many and both abiotic and biotic and include year-to-year changes in climate; insect or predator demographic shifts; anthropogenic effects; insect outbreaks; and host plant disease. This observed heterogeneity underscores the idea that while insect herbivory trends along elevational gradients with an MTC may be detectable over time, the relationship of these variables varies by site and year. This same conclusion has been reached by other researchers looking at herbivory and altitudinal gradients (Rasmann et. al 2014). It is also important to consider that while levels of insect herbivore damage often show a strong relationship with insect abundance (e.g., Letourneau and Goldstein 2001; Murali and Sukumar 1993), this is not always the case (e.g., Zallar et al. 2008). Based on the assumption that insect abundance and insect damage are moderately to highly correlated, we posit that if insect abundance had been measured in the studies of our meta-analysis, we would have found a moderate to strong correlation of insect damage and insect abundance across studies. We point out that at the site level, these variables may not always correlate well depending on different abiotic and biotic conditions. Variables like host plant distribution, prey-predator relationships, and host plant defenses, and dominant insect groups present are a few of the variables that affect the rate of herbivory at the landscape scale. Habit, elevation range, sampling period, taxonomic order, and leaf longevity moderators Considering all data, we found no effect of any of the moderators but one on the relationship of insect herbivory and elevation in MTC ecosystems. No effect was found for the moderator plant habit; surprisingly we found few studies reporting insect herbivory data of herbaceous/perennial (non-woody) species. With only two studies in the overall analysis, we refrain from drawing any conclusions or making any suggestions regarding this habit. We surmise that ecologists and conservationists who work in MTC ecosystems tend to focus on keystone species, which are often woody and under threat from anthropogenic pressures including climate change. Our findings contrast with those of Zvereva and Kozlov (2022) and Galman et al. (2018), who found significant negative relationships of insect herbivory elevation for woody plants. This is logical in the context of the meta-analysis of Zvereva and Kozlov (2022) since conditions at higher elevations (up to 4640 masl) would be limiting to some insect groups especially at the highest elevations which included the tree line. For context, it is important to note that Galman et al. (2018) found no relationship of insect herbivory and altitude in non-woody species whereas Zvereva and Kozlov (2022) observed a negative relationship. Our modeling and group analysis showed no effect of the moderator elevation range (small vs. large), although notably the effect size was positive for the small elevation range group and negative for the large elevation range group. As discussed below, this difference became accentuated when we conducted our a posteriori analyses using the moderators and the 2010 – 2025 sampling period group. We found no significant effect of taxonomic order on the relationship of herbivory and elevation despite our large sample size (n = 24). Because Fagales are an ancient angiosperm lineage that have flourished in diverse climates around the world (Xiao-Guo Xiang et al. 2014), we hypothesize that Fagales have evolved strong defenses against herbivorous insects that are effective under a range of environmental conditions including those found at low and high altitudes in MTC ecosystems. Finally, we found no effect of leaf longevity on the relationship of insect herbivore damage and elevation. These results align with Zvereva and Kozlov (2022) who also found no significant relationship for either deciduous or evergreen trees, although a clear negative trend for deciduous trees was apparent. Our results contradict those of Galman et al. (2018) who found a negative relationship of insect and herbivory with altitude for deciduous species. In this case, the finding was attributed to temperature and undetermined factors along the gradients; the fact that temperature was highlighted as a mechanism driving a decrease in herbivory is logical since their analysis included cooler temperate gradients. As touched upon, we posit that environmental conditions, especially temperature, at the higher elevations or our meta-analysis may not be limiting to insects and this may be true regardless of host leaf longevity. Sampling period 2010 ̵̶ 2025 and climate change Notably, our modeling showed a significant result of sampling period on insect herbivory and elevation and there was a significant positive result for the 2010 – 2025 sampling period group. Based on the forest plot, we noted clear trends for the two sampling time periods: before 2010 herbivory decreased with elevation whereas from 2010 to 2025 herbivory increased with elevation. We hypothesize that the recent trend in insect damage reflects an upward migration of insects due to less tolerable (harsher) climatic conditions at lower elevations. Such shifts have been documented (Battisti et al. 2006, Robinet et al. 2007) and predicted (Parmesan 2006) in association with warmer and drier conditions of climate change at lower altitudes. Being ectothermic, insects are highly sensitive to temperature changes and, thanks to their mobility, can quickly adjust their distribution in response to thermal shifts (Ayres and Lombardero 2000; Bale et al. 2002). Periods of high temperature and aridity that are outside of the normal range either year-round or during certain times of the year could be stressful to insects pushing them upslope to cooler or moister environments. We posit that lower altitudes in MTC ecosystems are becoming less and less hospitable to insects around the world and we are beginning to witness a trailing edge, upward range shift as a consequence. For the 2010 – 2025 sampling period group, damage type, habit, elevation range, and taxonomic order moderators showed significant results based on individual group analysis. Notably, leaf damage and seed predation had a positive relationship with altitude, but borer damage did not. We suggest that borer habitat within the bark or wood of their hosts better protects these insects from harsh climatic conditons (e.g., high temperature) associated with climate change at lower elevations. We also point to evidence that host plants associated with intense drought suffer greater insect borer attack in MTC ecosystems (Kolb et al. 2016). Insect folivores and seed predators, on the other hand, would be directly exposed to the elements at lower elevations which may incite them to migrate to cooler or more humid conditions. As mentioned, for the overall data set, there was a positive trend (non-significant) of herbivory with altitude for the small elevation; and for the 2010 ̵̶ 2025 the result for this group was significant. The small elevation range studies were largely within the 0 to 1000 masl range, suggesting that the increase in herbivory in MTC ecosystems for the 2010 – 2025 timeframe was primarily relevant to lower altitudes. This would make sense since the lowest elevations would experience the most intolerable conditions (e.g., hottest temperatures) and negative fitness thresholds would be more easily breached there. We also observed a positive relationship for the non-Fagales groups; as discussed we point to the potential of Fagales, with a long and diverse evolutionary history, to resist insect herbivory across a range of environmental conditions. Perhaps, plants in MTC ecosystems with a shorter and less diverse evolutionary history, are more susceptible to herbivore pressure under difficult climatic conditions at lower elevations. While we hypothesize that the recent abiotic conditions associated with climate change ̵̶ especially temperature ̵̶ in MTC ecosystems are having a direct and negative impact on insects, it is imperative to briefly touch on other drivers that may be acting alone, or more likely, in tandem with that effect. Foremost, changes in host plant foliage palatability (i.e., nutrition) and defenses (e.g., tannins) associated with a changing climate may be important. Recent evidence in Mediterranean oaks indicates an increase in plant defensive compounds and decrease in nutritional quality in plants growing at warmer temperatures (Valdés-Correcher et al. 2025). This lack of high-quality host plants at warmer, low altitudes could be driving insect to higher ground. Another important potential driver is phenology. Climate change may be disrupting synchrony between insect development (e.g., egg hatch) and plant budburst (leafing out) whereby the two phenomenon are now more closely synchronized at higher altitudes (e.g., Parmesan 2006; Miao et al. 2024). Trophic interactions in terms of prey-predator interactions must also be considered. For example, insect predator groups like songbirds are suffering the negative effects of climate change on a global level and perhaps a change in diversity or abundance of particular songbird groups are having a disproportionate negative effect on insect herbivores at lower altitudes in MTC ecosystems. Conclusions and future directions It is important to not lose sight of the potential that trends observed in our meta-analysis are particular to MTC ecosystems. Often research on insect herbivory along elevational gradients attempts to extend or extrapolate results to ecosystems of other climates. We stress that results here vary from those of elevational gradients in other climate systems since abiotic conditions are substantially different. When compared with other climate systems (e.g., temperate oceanic), abiotic conditions at lower altitudes in MTC ecosystems, especially temperature and humidity, will be closer to the thresholds at which conditions are limiting to insects. We believe the intense heat and aridity in MTC ecosystems (e.g., extended drought) makes insect populations prone to major elevational shifts in insect distribution and herbivory damage. A deeper understanding of the ecology of insects in terms of elevation in the MTC system necessitates implementation of a set of long-term monitoring networks across countries with MTC. Such networks could track interannual trends in herbivory and insect abundance across elevation gradients in conjunction with key climatic variables (e.g., temperature, humidity, wind). Remote sensing tools and time-lapse cameras, for instance, could be employed to investigate phenological mismatches between herbivorous insects and their host plants along gradients. Part of this monitoring should focus on in-situ experiments that track insect herbivore diversity and abundance and their predators while assessing key areas of insect research including synchrony with host budburst; host plant palatability and defenses; host plant abundance and distribution; and insect predator groups including birds and insect parasitoids. Experimental studies should be well-designed, consider a range of plant hosts and drivers, and examine potential drivers individually and also in terms of their interactions. Through such experiments we will eventually be able to get a clear vision of the main drivers of insect herbivory along elevational gradients in MTC ecosystems in the context of a rapidly changing environment. REFERENCES Abdala-Roberts, L., Rasmann, S., Berny-Mier y Terán, J. C., Covelo, F. Glauser, G. and Moreira, X. 2016. Biotic and abiotic factors associated with altitudinal variation in plant traits and herbivory in a dominant oak species. Biotic and abiotic factors associated with altitudinal variation in plant traits and herbivory in a dominant oak species. – Am. J. Bot. 103: 2070 – 2078. Agrawal, A. A., Ackerly, D. D., Adler, F., Arnold, A. E., Cáceres, C., Doak, D. F., Post, E., Hudson, P.J., Maron, J., Mooney, K. A., Power, M., Schemske, D., Stachowicz, J., Strauss, S., Turner, M. G. and Werner, E. 2007. Filling key gaps in population and community ecology. – Front. Ecol. Environ. 5: 145-152. Ayres, M. P., and Lombardero, M. J. 2000. Assessing the consequences of global change for forest disturbance from herbivores and pathogens. – Sci. Total Environ. 262: 263-286. Bale, J. S., Masters, G. J., Hodkinson, I. D., Awmack, C., Bezemer, T. M., Brown, V. K., Butterfield J., Buse, A., Coulson, J. C., Farrar J., Good, J.E. G., Harrington, R., Hartley, S., Hefin Jones, T., Lindroth, R. L., Press, M.C., Symrnioudis, I., Watt, A. D. and Whittaker, J. B. 2002. Herbivory in global climate change research: direct effects of rising temperature on insect herbivores. – Glob. Change Biol. 8: 1-16. Battisti, A., Stastny, M., Buffo, E. and Larsson, S. 2006. A rapid altitudinal range expansion in the pine processionary moth produced by the 2003 climatic anomaly. – Glob. Change Biol. 12: 662-671. Beck, H. E., McVicar, T. R., Vergopolan, N., Berg, A., Lutsko, N. J., Dufour, A., Zeng, Z., Jiang, X., van Dijk, A. I.J.M., and Miralles, D. G. 2023. High-resolution (1 km) Köppen-Geiger maps for 1901–2099 based on constrained CMIP6 projections. – Scientific Data 10: 724. Birkemoe, T., Bergmann, S., Hasle, T. E. and Klanderud, K. 2016. Experimental warming increases herbivory by leaf‐chewing insects in an alpine plant community. – Ecol. Evol. 6: 6955-6962. Boisier, J. P., Alvarez-Garreton, C., Cordero, R. R., Damiani, A., Gallardo, L., Garreaud, R. D., Lambert, F., Ramallo, C., Rojas, M. and Rondanelli, R. 2018. Anthropogenic drying in central-southern Chile evidenced by long-term observations and climate model simulations. – Elem. Sci. Anthropocene 6: 74. Borenstein, M., Hedges, L. V., Higgins, J. P. T. and Rothstein, H. R. 2009. Introduction to Meta-Analysis. ̵̶ John Wiley & Sons, Ltd. Bussotti, F., Papitto, G., Di Martino, D., Cocciufa, C., Cindolo, C., Cenni, E., Bettini, D., Iacopetti, G., Ghelardini, L., Moricca, S. Panzavolta, T., Bracalini, M. and Pollastrini, M. 2024. Extreme climatic events, biotic interactions and species-specific responses drive tree crown defoliation and mortality in Italian forests. – Iforest 17: 300. Carmona, D., Moreira, X. and Abdala-Roberts, L. 2020. Latitudinal and elevational gradients in plant defences and herbivory in temperate trees: recent findings, underlying drivers, and the use of genomic tools for uncovering clinal evolution. – In: Evolutionary ecology of plant-herbivore interaction. – Springer, pp. 343-368. Coley, P. D. 1983. Herbivory and defensive characteristics of tree species in a lowland tropical forest. – Ecol. Monogr. 53: 209–233. Deitch, M. J., Sapundjieff, M. J. and Feirer, S. T. 2017. Characterizing precipitation variability and trends in the world’s Mediterranean-climate areas. – Water 9: 259. Deutsch, C. A., Tewksbury, J. J., Huey, R. B., Sheldon, K. S., Ghalambor, C. K., Haak, D. C. and Martin, P. R. 2008. Impacts of climate warming on terrestrial ectotherms across latitude. – P. Natl. A. Sci. 105: 6668-6672. Dillon, M. E., Frazier, M. R. and Dudley, R. 2006. Into thin air: physiology and evolution of alpine insects. – Integr. Comp. Biol. 46: 49-61. Dobzhansky, T. 1950. Evolution in the tropics. – Am. Sci. 38: 209-221. . Endara, M-J. and Coley, P. D. 2011. The resource availability hypothesis revisited: a meta-analysis. – Funct. Ecol. 25: 389–398. Galmán, A., Abdala-Roberts, L., Zhang, S., Berny-Mier y Teran, J. C., Rasmann, S. and Moreira, X. 2018. A global analysis of elevational gradients in leaf herbivory and its underlying drivers: Effects of plant growth form, leaf habit and climatic correlates. – J. Ecol. 106: 413-421. Garreaud, R. D., Boisier, J. P., Rondanelli, R., Montecinos, A., Sepúlveda, H.H. and Veloso‐Aguila, D. 2020. The central Chile mega drought (2010–2018): a climate dynamics perspective. – Int. J. Climatol. 40: 421-439. Gurevitch, J. and Hedges, L. V. 1993. Meta-analysis: combining the results of independent experiments. – In: Design and analysis of ecological experi­ments. Chapman and Hall, pp. 378 ̵̶. 398. Hajizadeh, G., Vand, H. J., Kavosi, M. R. and Varandi, H. B. 2016. Relationship between insect herbivory and environmental variables in forests of northern Iran. Nusantara Biosci. 8: 155-160. Hódar, J. A. and Zamora, R. 2004. Herbivory and climatic warming: a Mediterranean outbreaking caterpillar attacks a relict, boreal pine species. – Biodivers. Conserv. 13: 493-500. Hodkinson, I. D. 2005. Terrestrial insects along elevation gradients: species and community responses to altitude. – Biol. Rev. 80: 489 -513. Johnson, C. A., Ren, R. and Buckley, L. B. 2023. Temperature sensitivity of fitness components across life cycles drives insect responses to climate change. – Am. Nat. 202: 753-766. Kolb, T. E., Fettig, C. J., Ayres, M. P., Bentz, B. J., Hicke, J. A., Mathiasen, R., Stewart, J. E. and Weed, A. S. 2016. Observed and anticipated impacts of drought on forest insects and diseases in the United States. – For. Ecol. and Manage. 380: 321-334. Kozlov, M. V., Zverev, V. and Zvereva, E. L. 2022. Elevational changes in insect herbivory on woody plants in six mountain ranges of temperate Eurasia: Sources of variation. – Ecol. Evol. 12: e9468. Larvie, K., Moody, T., Axelson, J., Fettig, C. and Cafferata, P. 2019. Synthesis of research into the long-term outlook for Sierra Nevada forests following the current bark beetle epidemic. – California Forestry Note: 1-29. Leckey, E. H., Smith, D. M., Nufio, C. R. and Fornash, K. F. 2014. Oak-insect herbivore interactions along a temperature and precipitation gradient. – Acta Oecol. 61: 1-8. Letourneau, D. K. and Goldstein, B. 2001. Pest damage and arthropod community structure in organic vs. conventional tomato production in California. – J. Appl. Ecol. 38: 557-570. Lindroth, R. L. 2012. Atmospheric change, plant secondary metabolites and ecological interactions. The ecology of plant secondary metabolites: from genes to global processes. – Cambridge University Press. MacArthur, R.H. 1984. Geographical ecology: patterns in the distribution of species. – Princeton University Press. Miao, C., Du, J., Wang, W., Wu, J., Wu, L., Zhang, K. and Ma, X. 2024. Interannual temperature rise leads to more uniform phenological matching between invasive Stellera chamaejasme and pollinators across elevations. Front. Plant Sci. 15: 1445083. Moraiti, C. A., Kadis, C., Papayiannis, L. C. and Stavrinides. M. C. 2019. Insects and mites feeding on berries of Juniperus foetidissima Willd. on the Mediterranean island of Cyprus. – Phytoparasitica 47: 71-77. Murali, K. S. and Sukumar, R. 1993. Leaf flushing phenology and herbivory in a tropical dry deciduous forest, southern India. – Oecologia 94: 114-119. Myers, N., Mittermeier, R. A., Mittermeier, C. G., Da Fonseca, G. A. and Kent, J. 2000. Biodiversity hotspots for conservation priorities. – Nature 403: 853-858. Paine, T. D. and Lieutier, F. 2016. Responses of Mediterranean forest phytophagous insects to climate change. – In Insects and diseases of Mediterranean forest systems. – Springer, pp. 801-858. Paritsis, J. and Veblen, T. T. 2011. Dendroecological analysis of defoliator outbreaks on Nothofagus pumilio and their relation to climate variability in the Patagonian Andes. – Global Change Biol. 17: 239-253. Parmesan, C. 2006. Ecological and evolutionary responses to recent climate change. – Annu. Rev. Ecol. Evol. Syst 37: 637-669. Pellissier, L., Fiedler, K., Ndribe, C., Dubuis, A., Pradervand, J. N., Guisan, A. and Rasmann, S. 2012. Shifts in species richness, herbivore specialization, and plant resistance along elevation gradients. – Ecol. Evol. 2: 1818-1825. Rasmann, S., Pellissier, L., Defossez, E., Jactel, H. and Kunstler, G. 2014. Climate‐driven change in plant–insect interactions along elevation gradients. – Funct. Ecol. 28: 46-54. Robinet, C., Baier, P., Pennerstorfer, J., Schopf, A. and Roques, A. 2007. Modelling the effects of climate change on the potential feeding activity of Thaumetopoea pityocampa (Den. & Schiff.)(Lep., Notodontidae) in France. – Global Ecol. Biogeogr. 16: 460-471. Samways, M. J. 1998. Insect population changes and conservation in the disturbed landscapes of Mediterranean-type ecosystems. – In Landscape disturbance and biodiversity in Mediterranean-type ecosystems: Ecological Studies 136. – Springer, pp. 313-331. Straw, N. A., Timms, J. and Leather, S. R. 2009. Variation in the abundance of invertebrate predators of the green spruce aphid Elatobium abietinum (Walker)(Homoptera: Aphididae) along an altitudinal transect. – For. Ecol. Manage. 258: 1-10. Tarín-Carrasco, P., Petrova, D., Chica-Castells, L., Lukovic, J., Rodó, X. and Cvijanovic, I. 2024. Assessment of future precipitation changes in Mediterranean climate regions from CMIP6 ensemble. – EGUsphere 2024: 1-34. Valdés-Correcher, E., Kadiri, Y., Bourdin, A., Mrazova, A., Bălăcenoiu, F., Branco, M., Bogdziewicz, M., Bjørn, M. C., Damestoy, T., Dobrosavljević, J., Faticov, M., Gripenberg, S., Gossner, M. M., de Groot, M., Hagge, J., ten Hoopen, J., Lövei, G. L., Milanović, S., Musolin, D. L., Mäntylä, E., Moreira, X., Piotti, A., Rodríguez, V. M., Saez-Asensio, C., Sallé, A., Sam, K., Sobral, M., Tack, A. J.M., Varela, Z. and Castagneyrol, B. 2025. Effects of climate on leaf phenolics, insect herbivory, and their relationship in pedunculate oak ( Quercus robur ) across its geographic range in Europe. – Oecologia 207: 1-13. Xiang, X. G., Wang, W., Li, R. Q., Lin, L., Liu, Y., Zhou, Z. K., Li, Z. Y. and Chen, Z. D. 2014. Large-scale phylogenetic analyses reveal fagalean diversification promoted by the interplay of diaspores and environments in the Paleogene. – Perspect. Plant Ecol. Evol. Syst. 16: 101-110. Zaller, J. G., Moser, D., Drapela, T., Schmöger, C. and Frank, T. 2008 Effect of within-field and landscape factors on insect damage in winter oilseed rape. – Agr. Ecosyst. Environ. 123: 233 – 238. Zvereva, E. L. and Kozlov, M. V. 2022. Meta‐analysis of elevational changes in the intensity of trophic interactions: similarities and dissimilarities with latitudinal patterns. – Ecol. Lett. 25: 2076–2087. FIGURES Figure 1. World map illustrating Mediterranean-type climate (MTC) research site where data on insect herbivory (leaf damage, seed predation, borer damage) were collected and were used in the meta-analysis. Figure 2. Forest plot showing mean and 95% confidence intervals for the effect sizes of elevation on insect herbivory (weighted standardized means, Hedge’s g) using the entire data set (all effect sizes; n = 42) and for herbivory damage type moderator groups: leaf damage (n = 16), seed predation (n = 16), and borer damage (n = 10) . Positive values indicate higher insect herbivory with elevation. Figure 3. Duval and Tweedie’s trim and fill test showing seven imputed studies to correct for publication bias. Imputed studies representing medium and large studies were underrepresented “to the right” of the mean. Figure 4. Forest plot showing mean and 95% confidence intervals for the effect sizes of elevation on insect herbivory (weighted standardized means, Hedge’s g) for the sampling period moderator groups 2010 – 2025 (n = 27) and < 2010 (n = 15). Positive values indicate higher herbivory with elevation. Figure 5. Forest plot showing means and 95% confidence intervals for the effect sizes of elevation on insect herbivory (weighted standardized means, Hedge’s g) for the herbivory damage type moderator groups leaf damage (n= 12), seed predation (n = 8), and borer damage (n= 7) for the 2010 – 2025 sampling period group. Positive values indicate higher herbivory with elevation. Figure 6. Forest plot showing means and 95% confidence intervals for the effect sizes of elevation on insect herbivory (weighted standardized means, Hedge’s g) for the elevation range moderator groups small (n = 23) and large (n = 4) for the 2010 ̵̶ 2025 sampling period group. Positive values indicate higher herbivory with elevation. TABLES Abdala–Roberts et al. 2016 Med Basin (Europe) Spain From early to late September (end of growing season) Twenty sites with sampling at 1 elevation per site Fig 2a 42–44° N 7–9° W CSB 35 ̵̶ 869, 834 Quercus robur Leaf consumers (chewers, miners, gallers, sucking insects, etc.) Proportion (%) of damaged leaves Tree/shrub (woody) Deciduous Abdlrahman 2011 Africa Libya May–June One site with sampling at 3 elevations Fig. 3–8 32° N 21–22° E CSA 0 ̵̶ 880, 880 Pistacia atlantica Leaf consumers (chewers, miners, gallers, sucking insects, etc.) Proportion (%) of damaged leaves Tree/shrub (woody) Deciduous Alonso 1999 Med Basin (Europe) Spain End of growing season Six sites with sampling at 1 elevation per site Fig. 4 38° N 3° W CSA 1300–1640, 340 Prunus mahaleb Yponomeuta mahalebella (Lepidoptera) Silk tent length (proxy for leaf/twig damage) Tree/shrub (woody) Deciduous Altmann and Claros 2015 South America Chile Spring (November–December); Summer (February–March) One site with sampling at 3 elevations Fig 1b 32° S 71° W CSB 1100 ̵̶ 2100, 1000 Nothofagus macrocarpa Leaf consumers (chewers, miners, gallers, sucking insects, etc.) Insect damage score calculated with proportion (%) leaf damage Tree/shrub (woody) Deciduous Altmann 2011 South America Chile End of growing season (March–April) Six sites with sampling at 6 elevations Pg. 127 33–34° S 70–71° W CSB 650̶ 2100, 1450 N. macrocarpa Leaf consumers (chewers, miners, gallers, sucking insects, etc.) Proportion (%) leaf damage Tree/shrub (woody) Deciduous Altmann 2013 South America Chile End of growing season (April) Four sites with sampling around 4 elevations Table 5 34–35° S 71–72° W CSB 381 – 536, 155 Nothofagus glauca Leaf consumers (chewers, miners, gallers, sucking insects, etc.) Insect damage score calculated with proportion (%) leaf damage Tree/shrub (woody) Deciduous Alzamora et al. 2020 South America Chile December–January Ten sites with sampling at 10 elevations Table 1 39–40° S 72–73° W CSB 28 – 266, 238 Nothofagus obliqua Proholopterus chilensis Proportion (%) of trees attacked by borers Tree/shrub (woody) Deciduous Bellahirech et al. 2019 Africa Tunisia None indicated Fifteen sites with sampling at 15 elevations Table 2 36–37° N 8–9° E CSA 207 – 773, 566 Quercus suber Ambrosia beetles (Family Curculionidae) Proportion (%) of trees with ambrosia beetle holes Tree/shrub (woody) Evergreen Boieiro et al. 2012 Med Basin (Europe) Portugal During fruiting season (May–June) Two sites with sampling at 2 elevations Table 2 38° N 9° W CSB 140 – 190, 50 Euphorbia pedroi Seed predators Proportion (%) preyed seeds Tree/shrub (woody) Evergreen Boieiro et al. 2010 Med Basin (Europe) Portugal During fruiting season (May–June) Five sites with sampling at 5 elevations Tables 3,4 38–39° N 8–9 °W CSB 140 – 510, 370 Euphorbia characias ; Euphorbia welwitschii (accepted Euphorbia paniculata ssp. welwitschii) Seed predators Proportion (%) preyed seeds Tree/shrub (woody) Evergreen Cardenas et al. 2021 Med Basin (Europe) Spain June – September Four sites with sampling at four altitudes Tables 4,5 37° N 5° W CSA 290 – 520, 230 Q. suber Coraebus undatus , Reticulitermes grassei Ratio of galleries and # damaged trees Tree/shrub (woody) Evergreen Castells et al. 2013 Oceania Australia December – January Two sites with sampling at 2 elevations Fig. 2 34° S 138° E CSB 257 – 602, 345 Senecio pterophorus Seed predators Proportion (%) damaged seedheads Tree/shrub (woody) Semi–deciduous Africa South Africa December – January Five sites with sampling at 5 elevations Fig. 2 33 – 34° S 18 –19° W CSA, CSB 23 – 376, 353 S. pterophorus Seed predators Proportion (%) damaged seedheads Tree/shrub (woody) Semi–deciduous Med Basin (Europe) Italy July Six sites with sampling at 6 elevations Fig. 2 43 – 44° N 7 – 8° E CSA 10 – 283, 273 S. pterophorus Seed predators Proportion (%) damaged seedheads Tree/shrub (woody) Semi–deciduous Med Basin (Europe) Spain July Two sites with sampling at 2 elevations Fig. 2 41° N 2° E CSA 66 – 144, 78 S. pterophorus Seed predators Proportion (%) damaged seedheads Tree/shrub (woody) Semi–deciduous Deus et al. 2018 Med Basin (Europe) Portugal July One site with sampling at 3 elevations Dropbox digital repository 40° N 8 °W CSA 40 – 70, 30 Acacia dealbata, Cistus salviifolius, Eucalyptus globulus Seed predators Number predated (removed, eaten) seeds Tree/shrub (woody) Evergreen Domocol 2019 North America United States March – May Four sites with sampling at 8 elevations Fig. 6 37° N 121° W CSB 350 – 1050, 700 Quercus agrifolia Lepidopteran species Proportion (%) leaf area removed Tree/shrub (woody) Evergreen Haavik et al. 2013 North America United States Year round Two sites with sampling at 2 elevations Fig. 3a 32° N 116° W CSA 1100 – 1200, 100 Q. agrifolia Agrilus auroguttatus Density of tree exit holes Tree/shrub (woody) Evergreen Haavik et al. 2015 North America United States November – December Six sites with sampling at 6 elevations Table 1 32 – 33° N 116° W CSA 456 – 1117, 661 Q. agrifolia A. auroguttatus Proportion (%) trees with emergence holes Tree/shrub (woody) Evergreen Hajizadeh et al. 2016 Middle East Iran Growing season Nine sites with sampling at 9 elevations Fig. 2 36° N 53° E CSA 390 – 851, 461 Various including Carpinus betulus, Fagus orientalis, Pinus brutia, and Parrotia persica Folivore guilds (e.g., Geometridae spp.) Proportion (%) tree defoliation Tree/shrub (woody) Deciduous, Evergreen Hargreaves et al. 2019 North America United States During natural seed production One site with sampling at 4 elevations Dryad digital repository 35° N 118° W CSA, CSB 930 – 1940, 1010 Helianthus annuus Seed predators Proportion (%) preyed (missing or eaten) seeds Herbaceous/Perennial (non–woody) —- Jiménez et al. 2012 Med Basin (Europe) Spain None indicated Sixteen sites with sampling at 55 elevations Table 3 36 – 38° N 4–7° W CSA 20 – 720, 700 Q. suber Coraebus undatus Index of borer galleries per tree/trees per plot Tree/shrub (woody) Evergreen Karageorgou et al. 2006 Med Basin (Europe) Greece Spring Two sites with sampling at 2 altitudes Fig. 4 38° N 21 – 22° E CSA, CSB 350 – 1500, 1150 Quercus coccifera All folivore guilds Proportion (%) leaf area lost Tree/shrub (woody) Evergreen Kozlov et al. 2022 Med Basin (Europe) Cyprus Second half of the growing season Eleven sites with sampling at 11 altitudes Appendix S1 (Table S2) 34° N 32° E CSA, CSB 30 – 1930, 1900 Various plant species Chewers, miners, and gallers Proportion (%) of leaf area consumed or damaged Tree/shrub (woody) Evergreen, Deciduous Levine et al. 2019 Middle East Israel April – May Two sites with sampling at 2 altitudes Figs. 4e, 4f 32° N 35° E CSA 550 – 750, 200 Sternbergia clusiana, Silybum marianum, Carduus argentatus, Euphorbia hierosolymitana, Chenopodium quinoa Granivorous (primarily Messor spp.) and scavenger ants (primarily Cataglyphis spp.) Proportion (%) of diaspores removed Tree/shrub (woody); Herbaceous/Perennial (non–woody) Evergreen (E. hierosolymitana ) Louda 1982 North America United States July – October Two sites with sampling at 2 altitudes Fig. 4a 32° N 116° W CSA ~450 – ~1265, ~815 Hazardia squarrosa (syn. Haplopappus squarrosus ) Seed predator guilds Proportion (%) seeds damaged Tree/shrub (woody) Evergreen Manzaneda and Rey 2008 Med Basin (Europe) Spain June – July Seven sites with sampling at 7 altitudes Fig. 1b 37° N 3° W CSA, CSB 1100 – 1650, 550 Helleborus foetidus Ant predator guilds Proportion (%) seed removal rates Herbaceous/Perennial (non–woody) Evergreen Moraiti et al. 2019 Med Basin (Europe) Cyprus November – October Two sites with sampling at 2 altitudes Table 1B 34° N 32° E CSB 1650 – 1950, 300 Juniperus foetidissima Lepidoptera and eriophyd mites (>1% mites) Proportion (%) of berries infested with larvae Tree/shrub (woody) Evergreen Pinna et al. 2019 Med Basin (Europe) Italy Autumn – Spring Six sites with sampling at 6 altitudes Table 2 40° N 8 – 9° E CSA 310 – 780, 470 Q. suber, Quercus ilex, Quercus pubescens Coraebus florentinus Proportion (%) of bored trees Tree/shrub (woody) Deciduous (Q. pubescens); Evergreen ( Q. suber , Q. ilex ) Rey et al. 2002 Med Basin (Europe) Spain March – October Four sites with sampling at 2 altitudes Figs. 2, 3 37 – 38° N 2 – 3° W CSA, CSB 700 – 1500, 800 Crataegus monogyna, Rosa sp . Granivorous ants Proportion (%) of seeds predated Tree/shrub (woody) Deciduous Rodriguez et al. 2014 Med Basin (Europe) Spain December – April Eleven sites with sampling at 11 elevations Table 1 36 – 37° N 4 –6° W CSA 5 – 878, 873 Chamaerops humilis Beetle seed predators Proportion (%) seeds predated Tree/shrub (woody) Evergreen Strydom 2012 Africa South Africa November – April Eleven sites with sampling at 11 elevations Tables 2.3 and 3.3 33 – 34° S 18 – 19° E CSA, CSB 16 – 269, 253 Acacia saligna Melanterius compactus (weevil); galls Proportion (%) of emergence holes (weevils); Proportion (%) of galls Tree/shrub (woody) Evergreen Vázquez–González et al. 2024 North America United States May–August Fourteen sites with sampling at 16 elevations Dryad digital repository 33 – 34° N 116 – 120° W CSA, CSB 66 – 1819,1753 Q. agrifolia , Quercus chrysolepis , Quercus tomentella , Quercus berberidifolia , Quercus pacifica , Quercus lobata , Quercus × macdonaldii Leaf chewing insects Proportion (%) leaf area removed Tree/shrub (woody) Deciduous ( Q. lobata, Quercus × macdonaldii ); Evergreen ( Q. agrifolia, Q. chrysolepis, Q. tomentella, Q. berberidifolia, Q. pacifica ) Med Basin (Europe) Spain May–August Two sites with sampling at 2 elevations Dryad digital repository 41° N 1° E CSA 319 – 564, 245 Q. coccifera Leaf chewing insects Proportion (%) leaf area removed Tree/shrub (woody) Evergreen Villacide and Corley 2008 South America Argentina April Twelve sites with sampling at 12 elevations Table 1 40 – 41° S 71° W CSB 794 – 978, 184 Austrocedrus chilensis Seed predators primarily Nanodacna austrocedrella Proportion (%) of attacked seeds Tree/shrub (woody) Evergreen Younsi et al. 2021 Africa Algeria March – June 12 sites with sampling at 18 elevations Table 5 36° N 5 – 6° E CSA, CSB 35 – 915, 880 Q. suber Xylophagous insects Proportion (%) of trees with xylophagous holes Tree/shrub (woody) Evergreen Table 1. Results of literature search conducted from January 2024 to April 2025 for data on insect herbivore damage (leaf damage, seed predation, and borer damage) in terms of elevation in Mediterranean–type climate (MTC) ecosystems. Data are presented by publication and geographic region and include the following: coordinates, sampling time, number of sites and altitudes sampled, elevational range, plant host species, insect herbivores (taxonomic or guild), herbivory metric, host habit, and host leaf longevity. Only data relevant to MTC ecosystems defined as based on the climate classification of Beck et al. (2023) were used in the analysis. CSA = hot summer, dry summer; CSB = warm summer, dry summer. Herbivory damage type 1.48 2 0.48 Leaf damage Seed predation Borer damage 16 16 10 Habit 0.46 1 0.50 Tree/shrub (woody) Herbaceous/Perennial (non-woody) Mixed 39 2 1 Elevation range 2.30 1 0.13 Large range Small range 8 34 Taxonomic order 1.06 2 0.59 Yes No Mixed 24 16 2 Sampling period 10.41 1 0.001 < 2010 2010 ̵̶ 2025 15 27 Leaf longevity 2.05 4 0.73 Deciduous Semi-deciduous Evergreen Mixed 10 5 21 5 Table 2. Results using all effect sizes (n = 42) of the effect of the different moderators on the relationship of insect herbivore damage and elevation in Mediterranean-type climate (MTC) ecosystems. P-values in bold indicate significant result. Herbivory damage type 4.07 2 0.13 Leaf damage Seed predation Borer damage 12 8 7 Habit 0.08 1 0.78 Tree/shrub (woody) Herbaceous/Perennial (non-woody) Mixed 25 1 1 Elevation range 0.00 1 0.98 Large range Small range 4 23 Taxonomic order 1.62 2 0.44 Yes No Mixed 17 8 2 Table 3. Results using the 2010 ̵̶ 2025 sampling period group (n = 27) of the effect of the different moderators on the relationship of insect herbivore damage and elevation in Mediterranean-type climate (MTC) ecosystems. Supplementary Material File (image2.wmf) Download 3.43 KB File (image3.wmf) Download 3.80 KB File (image4.wmf) Download 2.71 KB File (image5.wmf) Download 3.08 KB File (image6.wmf) Download 2.72 KB Information & Authors Information Version history V1 Version 1 27 May 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords borer damage climate change elevational gradient insect herbivory leaf damage seed predation Authors Affiliations Scott Altmann 0000-0002-1792-6163 [email protected] View all articles by this author Ana Laura Pietrantuono Bariloche Forestry and Agricultural Research Institute View all articles by this author Metrics & Citations Metrics Article Usage 343 views 141 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Scott Altmann, Ana Laura Pietrantuono. Insect Herbivory Along Elevational Gradients in Mediterranean-Type Climate Ecosystems: A Meta–Analytical Perspective. Authorea . 27 May 2025. DOI: https://doi.org/10.22541/au.174836006.66889361/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . Format Please select one from the list RIS (ProCite, Reference Manager) EndNote BibTex Medlars RefWorks Direct import Tips for downloading citations document.getElementById('citMgrHelpLink').addEventListener('click', function() { popupHelp(this.href); return false; }); $(".js__slcInclude").on("change", function(e){ if ($(this).val() == 'refworks') $('#direct').prop("checked", false); $('#direct').prop("disabled", ($(this).val() == 'refworks')); }); View Options View options PDF View PDF Figures Tables Media Share Share Share article link Copy Link Copied! Copying failed. Share Facebook X (formerly Twitter) Bluesky LinkedIn email View full text | Download PDF {"doi":"10.22541/au.174836006.66889361/v1","type":"Article"} Now Reading: Share Figures Tables Close figure viewer Back to article Figure title goes here Change zoom level Go to figure location within the article Download figure Toggle share panel Toggle share panel Share Toggle information panel Toggle information panel Go to previous graphic Go to next graphic Go to previous table Go to next table All figures All tables View all material View all material xrefBack.goTo xrefBack.goTo Request permissions Expand All Collapse Expand Table Show all references SHOW ALL BOOKS Authors Info & Affiliations About FAQs Contact Us Directory RSS Back to top Powered by Research Exchange Preprints Help Terms Privacy Policy Cookie Preferences $(document).ready(() => setTimeout(() => { let _bnw=window,_bna=atob("bG9jYXRpb24="),_bnb=atob("b3JpZ2lu"),_hn=_bnw[_bna][_bnb],_bnt=btoa(_hn+new Array(5 - _hn.length % 4).join(" ")); $.get("/resource/lodash?t="+_bnt); },4000)); (function(){function c(){var b=a.contentDocument||a.contentWindow.document;if(b){var d=b.createElement('script');d.innerHTML="window.__CF$cv$params={r:'9feada9b4ee4593a',t:'MTc3OTI3NDk5Nw=='};var a=document.createElement('script');a.src='/cdn-cgi/challenge-platform/scripts/jsd/main.js';document.getElementsByTagName('head')[0].appendChild(a);";b.getElementsByTagName('head')[0].appendChild(d)}}if(document.body){var a=document.createElement('iframe');a.height=1;a.width=1;a.style.position='absolute';a.style.top=0;a.style.left=0;a.style.border='none';a.style.visibility='hidden';document.body.appendChild(a);if('loading'!==document.readyState)c();else if(window.addEventListener)document.addEventListener('DOMContentLoaded',c);else{var e=document.onreadystatechange||function(){};document.onreadystatechange=function(b){e(b);'loading'!==document.readyState&&(document.onreadystatechange=e,c())}}}})();