Agricultural practices improve breeding success of indigenous frogs in restored rice paddies: A case study from the Miyajima Wetland, Japan

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Naito, Yuki Kimura, Motoshi Hiratsuka This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9126504/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 9 You are reading this latest preprint version Abstract Rice paddies have played an important role as a substitute habitat for wetland species. However, environmental changes and the abandonment of rice paddies have led to a decline in the number of wetland species. Moreover, rice paddies are vital habitats for sustaining the population of pond-breeding frog species. However, it remains unclear how agricultural practice influences the sustainability of frog species. In this study, we conducted surveys in 13 restored rice paddies with different management histories and one irrigation pond in the Mikajima Wetland to investigate the characteristics of the rice paddies and the relationship between the characteristics and breeding success of the Japanese brown frog ( Rana japonica ). We found 134 egg masses at 14 sites, and monitored them until they hatched, died, or were lost; environmental factors, such as water temperature and depth, were recorded. First, we conducted a principal component analysis to determine the study site characteristics. Second, we constructed generalized additive mixed models to investigate the relationship between environmental factors and the number of new egg masses, hatching success, and number of days until hatching. Our results showed that the study sites were characterized by environmental factors associated with common management practices, irrigation and weed control. The breeding success of R. japonica was related to various aspects of aquatic habitats alternating between agricultural practices, and therefore, the agricultural practices can be practical measures for improving the environmental conditions in rice paddies to create preferable breeding and egg-rearing habitat for R. japonica . agroecosystem amphibian restoration conservation Figures Figure 1 Figure 2 Figure 3 Introduction Rice paddies and associated areas, such as irrigation ponds and secondary forests, are typically connected via irrigation channels (Washitani 2001 ) and play an essential role as substitute habitats for wetland species (Lawler 2001 ). Rice paddy ecosystems have been established over the long history of rice cultivation in Japan (Yamazaki 2005); however, since the 1950s, the modernization of rice paddies, including land consolidation projects, led to the degradation of rice paddies as habitats for wetland species (Natuhara 2013; Katayama et al. 2015 ), and many common species in these areas, such as frogs, are now endangered (Hasegawa et al. 2000 ; Japan Integrated Biodiversity Information System 2024 ). Moreover, as the population of farmers has aged, more rice paddies have been abandoned and have dried out and lost their function as habitat for wetland species (Fujioka and Lane 1997 ; Uematsu et al. 2010 ; Katayama et al. 2015 ). To create suitable habitats for wetland species under these circumstances, the restoration of wetland environments and resumption of agricultural practices of rice paddies have been suggested, however their effects have not been well studied (Kidera et al. 2018 ; Matsushima et al. 2023 ). In addition to the basic knowledge of the life histories of wetland species, a better understanding of the relationship between the life histories, environmental factors, and agricultural practices is required to develop practical restoration measures. In terms of suitability as restoration sites, modernized rice paddies have reduced functions as habitats for wetland species, whereas traditional rice paddies remaining in small-scale arable land in small valleys (called “yatsuda”) (Kurniawan et al. 2021 ) exhibit high restorative potential as a wetland environment, because some yatsuda and associated areas have preserved various lentic habitats with high connectivity (Kidera et al. 2018 ; Naito et al. 2025 ). Yatsuda are also being abandoned because of the aging farming population (Katayama et al. 2015 ), but the changes in environmental factors after abandonment are still not well understood. To develop effective conservation measures for wetland species, we must investigate how environmental factors change after agricultural practices are ceased. In this study, we focused on frogs found in rice paddies, as they are representative species in rice paddy ecosystems (Moriyama 1997 ). Because frogs need stable aquatic habitats for their egg and larval life stages (Snodgrass et al. 2000 ; Pearl et al. 2005 ; Karraker and Gibbs 2009 ), understanding how various abiotic and biotic aquatic environmental factors affect their reproductive success is essential for sustaining their populations (Rudolf and Rodel 2005 ). A comprehensive study of the relationship between environmental factors and reproductive success of frogs in spatiotemporally heterogeneous inundated habitats (Kellner and Green 1995 ; Goldingay and Newell 2005 ), and how aquatic habitats vary depending on rice paddy management, are essential for understanding the interaction between agricultural practices and frog population dynamics. We conducted our study at a yatsuda area in the Mikajima Wetland, where we found frog assemblages in restored rice paddies with various management histories and irrigation ponds (Naito et al. 2025 ); thus, multiple types of lentic habitats were available as study sites. In this study, we aimed to determine how environmental factors differ among rice paddies with different management histories and irrigation ponds, and how do environmental factors influence the breeding success of indigenous frog species. Specifically, we examined four groups of study sites consisting of rice paddies actively cultivated, fallow for two and five years, and an irrigation pond. We evaluated preferred breeding habitat conditions, egg survival, and the number of days to hatching to assess reproductive success. Finally, we discussed how rice paddy environments differ by management histories and how agricultural practices influence the reproductive success of R. japonica by altering rice paddy environments. Methodology Study area: This study was conducted in the Mikajima Wetland in the Sayama Hills, Tokorozawa City, Saitama Prefecture. The Sayama Hills cover approximately 3500 ha of forested and agricultural land and belong to six municipalities in Saitama Prefecture and the Tokyo metropolitan area. The satoyama landscape (socio-ecological production landscape) (Morimoto 2011 ) in this area, which includes the yatsuda areas, has been maintained and conserved by local people and the government, despite its proximity to Tokyo. Historically, a part of the Mikajima Wetland was converted to yatsuda and managed by farmers. The yatsuda and wetland areas together supported the wetland species. Our study area was in one of the yatsuda areas in the Mikajima Wetland. No land consolidation and improvement projects have been conducted in the study area, and the slopes surrounding the yatsuda area are primarily covered by secondary forests and grasslands. Over a 10-year period from 2014 to 2023, the mean annual precipitation and temperature in the area were 1519 mm and 15.1°C, respectively (Japan Meteorological Agency 2024 ). Farmers managed rice production in the area until they abandoned the rice paddies in 1970s, and thereafter, Waseda University and Saitama Midori-no-Mori Nature Park managed this area to conserve the wetland ecosystem. In the Waseda University-managed area, as one of the conservation measures for wetland ecosystem, four rice paddies were restored in 2002, three were restored in 2008, 2009, and 2010, and they were rotationally cultivated except the first group restored in 2002. The second group, which included three rice paddies restored in 2008, was cultivated from 2013–2015, the third group (restored in 2009) was cultivated from 2016–2018, and the fourth group (restored in 2010) was cultivated from 2019–2021; the second group was then cultivated again in 2022. We chose these 13 rice paddies as our study sites (Fig. 1 ). The first group of rice paddies was located upstream of the remaining paddies; therefore, they were referred to as upper rice paddies (UR1–UR4). The other rice paddies recently underwent cultivation in 2016–2018, 2019–2021, and 2022–present, and thus, were referred to as follows: rice paddies fallow for two years (FT1–FT3), rice paddies fallow for five years (FF1–FF3), and actively cultivated rice paddies (RP1–RP3) (Fig. 1 ). Owing to the lack of land consolidation and improvement projects, all paddies remained wet because of water flow and seepage from the surrounding environments. One irrigation pond (IP) connected to the rice paddies by the Sunagawa River was also investigated in this study (Fig. 1 ). The IP was included in our study sites because it is a common feature in yatsuda areas and is an important aquatic habitat for wetland species. The IP was surrounded by forest with deciduous trees (Konara Oak [ Quercus serrata ] and Japanese Snowbell [ Styrax japonicus ]), and the branches covered parts of the water surfaces. The IP was located at the uppermost part of the Sunagawa River and the Sunagawa River supplied water to all paddies, except the UR1–UR4. Water in FT1–FT3 flowed down to FF1–FF3 and subsequently to a downstream reed field. Water from RP1–RP3 also flowed into the reed fields. The water levels of RP1–RP3 decreased to a few centimeters during the transplanting period between May and June, and the harvesting period in September, but generally remained inundated throughout the year. All paddies were surrounded by vegetated levees that were 1–2 m wide and 50–70 cm high. The riparian vegetation was mowed to a height of several centimeters two or three times a year. The predominant vegetation in the UR1–UR4 and FT1–FT3 were common reeds ( Phragmites australis ), but the FT1–FT3 also contained Hera-omodaka ( Alisma canaliculatum ) and Konagi ( Monochoria vaginalis ), which are common species found in rice paddies in Japan. Study species: Japanese brown frog ( Rana japonica ) We chose R. japonica for this study because it is a common species in yatsuda areas, but its population has been decreasing (Tomioka 2000 ; Osawa and Katsuno 2002 ; Zheng et al. 2021 ). This species originates in the north so adapted to cool climates (Kuramoto et al. 1971 ). Breeding occurs from January to March in still water, and metamorphosis occurs from May to June (Matsui and Maeda, 2018 ). One female frog spawn one egg mass containing 500–3000 eggs during a breeding season (Matsui and Mori 2021 ). This species prefers open areas as breeding sites because vegetation covering the water surface interferes with breeding behavior (Kadowaki 2002 ). The critical thermal maximum of their embryos is 33°C, and the critical thermal minimum is slightly higher than 4°C; for development, the highest temperature the embryos can withstand is 29°C and the lowest is also slightly higher than 4°C (Kuramoto et al. 1971 ). R. japonica spends its non-breeding season in the secondary forest surrounding the rice paddies (Matsushima et al. 2023 ). The body lengths (snout-to-vent) of mature males and females are 34–63 mm and 43–67 mm, respectively (Matsui and Mori 2021 ). This species is included in the list of 31 prefecture-level endangered species (Ministry of Environment, Japan 2024 ). Field survey Environmental factors: We placed data loggers (Tidbit v2, Onset Computer Corporation, Bourne, MA, USA) in the IP, and rice paddies (UR4, FF1, FT2, FT3, RP1, and RP3) where the water level was sufficiently deep to install loggers and record the water temperature every 30 min during the survey period. We set two data loggers approximately 1 m aboveground, one near the IP, and one in FF1, to record the air temperature every 30 min during the survey period. We obtained precipitation data for Tokorozawa City for the study period from the Japan Meteorological Agency (Japan Meteorological Agency 2024 ). We recorded the amount of water surface covered by vegetation based on visual observation for each study site and calculated the water surface area of each study site using ArcGIS (version 10.8; ESRI Inc., Redlands, California, USA) based on an aerial photograph taken by an unmanned aerial vehicle (Phantom 4 Pro V2.0 DJI, Guangdong, China) on 12 May 2023. We obtained the point solar radiation in the middle of each study site using ArcGIS with a 5-m mesh digital elevation model (Geospatial Information Authority of Japan 2023). Egg masses: We walked a circuit of levees and banks at each site and numbered all egg masses found. We prepared a map of each study site based on the aerial photograph taken on 12 May 2023 and recorded the location of each egg mass. To avoid double counting, we referred to the developmental stage table described by Gosner ( 1960 ) and checked the developmental stage of each egg mass to ensure that it was newly spawned. For each egg mass, we recorded the species (Uchiyama 2005 ), water depth (measured manually with a folding ruler), and condition (hatched, dead, or lost). When > 90% of the eggs in an egg mass hatched or died, we considered the egg mass to be hatched or dead. When we could not find an egg mass once we returned to its recorded location, we considered the egg mass lost. We conducted surveys every two or three days between 10:00 and 14:00 from 17 February to 10 April 2023 (18 total surveys). Statistical analysis We conducted principal component analysis (PCA) of the main environmental factors characterizing each study site group to investigate how environmental factors vary among rice paddies with different management histories and irrigation ponds. We used the following environmental factors for the analysis: vegetation cover and the mean values of maximum daily water temperature, water temperature, minimum daily water temperature, solar radiation, and water depth during the study period. Statistical analyses were performed using R software (version 4.3.3; R Development Core Team 2024 ). To determine R. japonica ’s preferred environment for breeding and egg-rearing habitats, we constructed three generalized additive mixed models (GAMMs) for (1) the number of newly found egg masses, (2) the hatching success of each egg mass, and (3) the number of days each egg mass took to hatch successfully. The response variable for (1) was the mean number of new egg masses found at each study site in a day divided by the number of days between the previous and current days. For (2) and (3) the response variables were the hatching success of each egg mass and the number of days each egg mass took to hatch successfully, respectively. The candidate explanatory variables for (1) were vegetation cover and the mean values of the following environmental factors between the previous survey day and the day before the survey: precipitation, temperature, minimum daily temperature, water temperature, minimum daily water temperature, solar radiation, water depth at the location where a new egg mass was found, and vegetation cover. These means were used because frogs typically spawn at night, while our surveys were conducted during the day. For (2), the candidate explanatory variables were survey day (number of days since egg masses were first observed in the study area, March 14), vegetation cover, water surface area and the mean values of environmental factors between the day an egg mass was first detected and the day it was confirmed to have completely hatched or died: water temperature, minimum daily water temperature and solar radiation. For (3), the candidate explanatory variables were survey day, vegetation cover, water surface area and the mean values of environmental factors between the day the first egg mass was detected and the day it was confirmed to have completely hatched: water temperature, minimum daily water temperature and solar radiation. Air and water temperature data were obtained from the data logger installed closest to each study site. For each model, Pearson’s correlation analysis was used to assess correlations among continuous environmental variables. Variables with strong correlation ( r ≥ 0.6) were excluded from candidate explanatory variables to avoid strong multicollinearity. We set the error structure of the response variable as Poisson with log link function for model (1) and (3), whereas binominal with a logit link function for model (2). The log of the water surface area was included as an offset term in model (1). To account for potential nonlinear relationships between response and explanatory variables, the following factors were included in models as smooth terms: survey day in model (1), the mean water depth in model (2) and (3). In all models, study site group was included as a random intercept because observations within the same site category were expected to be more similar than those for different site categories. Statistical analyses were performed using the “gamm4” package in R. Statistical significance was set at P < 0.05. Results Field survey Environmental factors:It rained on 10 of the 27 days between the day before the first egg mass was found (11 March) and day when all egg masses had hatched, died, or been lost (6 April). During this time, the study area received 3.5 ± 1.2 mm (range, 0–22 mm) of precipitation per day. The mean ± standard error (SE) and the minimum and maximum temperature in the study area between 11 March and 6 April were 11.47 ± 0.15 °C (range, 0.08–27.1 °C) and 11.50 ± 0.14 °C (range, 0.33–23.62 °C), respectively (Table 3). The mean temperatures were similar, but the temperature range was greater at the IP. The mean ± SE and the minimum and maximum water temperature at IP, UP4, FF1, FT2, FT3, RP1, and RP3 sites between 11 March and 6 April were 10.23 ± 0.04 °C (range, 7.77–12.80 °C), 13.27 ± 0.15 °C (range, 2.40–29.7 °C), 10.60 ± 0.05 °C (range, 5.57–14.24 °C), 13.44 ± 0.12 °C (range, 4.32–26.01 °C), 14.83 ± 0.10 °C (range, 7.92–24.48 °C), 10.28 ± 0.06 °C (range, 4.38–19.32 °C), and 13.75 ± 0.08 °C (range, 7.59–23.35 °C), respectively. There were various thermal environments in the study area. We calculated the solar radiation, water surface area (AREA), and vegetation cover for each study site. The mean ± SE of solar radiation between 11 March and 6 April in each study site group were 6244 ± 28, 5954 ± 53, 6110 ± 47, 6394 ± 49, and 1572 ± 241 kWh/m 2 , respectively. The area was the largest at FF3 (273.0 m 2 ) and smallest at UR4A (2.5 m 2 ). The mean ± SE of the water surface area and vegetation cover of each study site group were as follows: IP, 224 m 2 and 3%; URs, 14.8 ± 7.9 m 2 and 55.9 ± 9.3%; FFs, 0 m 2 and 100 ± 0%; FTs, 95.7 ± 88.7 m 2 and 6.7 ± 1.2%; RPs, 227.4 ± 16.1 m 2 , and 5 ± 0% (Table 3). No surface water was observed in the FFs during the study period; consequently, no egg masses were found. Egg masses: During the 18 surveys conducted over the study period, we found 134 egg masses of R. japonica and nine egg masses (six in FTs and three in RPs) of the Montane brown frog ( R. ornativentris) . New R. japonica egg masses were recorded from 14–30 March at all study sites, except UR3 and FF1–FF3 (Table 1). A Japanese common toad (Bufo japonicus formosus Boulenger, 1883) spawning event occurred between 27 and 30 March at the IP ; subsequently, the number of B. japonicus egg masses did not appear to increase, and they were not found at any other sites. The numbers of R. japonica egg masses and the mean ± SE of water depth at which each egg mass was found were as follows: IP, 35 at 12.8 ± 0.5 cm; URs, 40 at 3.7 ± 0.5 cm; FFs, 0; FTs, 32 at 3.7 ± 0.4 cm; and RPs, 27 at 6.4 ± 0.5 cm (Table 2). Because there were very few R. ornativentris and B. japonicus egg masses compared with that of R. japonica , we assumed that interspecific interactions had little influence on R. japonica . Egg mass hatching: The hatched proportion of each egg mass was recorded at each survey until all egg masses had hatched or died. We found completely hatched egg masses in the study area on 27 March at RP3 and 6 April at UR1, FT1, FT3, RP2, and RP3. However, we lost all 35 egg masses in the IP, because the egg masses moved to the deep area of the IP, and two and four in FT3 and RP3, respectively, because the egg masses moved to the middle of the rice paddies, thus, we were unable to observe them. We tracked 93 egg masses from the day they were deposited to the day they completely hatched or died. We found 12 dead egg masses; three in UR4 were floating on the water surface, one in FT2 and six in FT3 were broken and scattered, two in RP2 were brown in color and displayed no further development, and two in RP3 were desiccated. The overall hatching success rate was 87%. The mean ± SE of days each egg mass took to completely hatch were 14.9 ± 0.7, 11.6 ± 0.5, and 11.6 ± 0.55 days in the URs, FTs, and PRs, respectively (Table 2). Statistical analysis The PCA results showed that our study site groups were mainly characterized by two principal components (PC1 and PC2) (Table 4). PC1 was positively correlated with the mean values of water depth and minimum daily water temperature and negatively correlated with vegetation cover. PC2 was positively correlated with the mean values of water temperature and maximum daily water temperature. PC1 and PC2 accounted for 42% and 33% of the variance, respectively. PC1 was associated with the factors mainly controlled by agricultural practices and PC2 was associated with aquatic thermal environment conditions (Fig. 2). Model analysis (1) Preferred breeding sites:Based on the Pearson’s coefficient values, we excluded the mean minimum daily water temperature from the explanatory variables. We constructed a GAMM with the mean number of new egg masses as the response variable and vegetation cover and the mean values of precipitation, temperature, water temperature, minimum daily temperature, solar radiation, and water depth (at which new egg masses were found) as explanatory variables ( n = 134). The smooth term estimated for the number of days was statistically significant (edf = 1.1, Chi.sq = 7.59, P < 0.01). The number of new egg masses was positively correlated with the mean precipitation and vegetation cover, and negatively correlated with the mean values of temperature, minimum daily temperature, and water depth (Table 5). Additionally, the number of new egg masses increased from day 1 until the end of the surveys. (2) Hatching success: Based on the Pearson’s coefficient values, we excluded vegetation cover and the mean values of water temperature and solar radiation from the explanatory variables. We constructed a GAMM with the hatching success as the response variable and survey day, water surface area and the mean minimum daily water temperature as explanatory variables ( n = 93). The smooth term estimated for the mean water depth was statistically significant (edf = 6.1, Chi.sq = 17.05, P < 0.05). The hatching success was positively correlated with the mean minimum daily water temperature and negatively correlated with water surface area (Table 6). The hatching success increased from very shallow to approximately 3 cm deep, decreased at approximately 4 cm deep, increased at approximately 6 cm deep, and subsequently decreased at greater depths (Fig. 3). (3) Number of days until hatching: Based on the Pearson’s coefficient values, we excluded vegetation cover and the mean solar radiation from the explanatory variables. We constructed a GAMM with the number of days to hatch as the response variable and survey day, water surface area and the mean values of water temperature and minimum daily water temperature as the explanatory variables ( n = 81). The smooth term estimated for the mean water depth was not statistically significant (edf = 1, Chi.sq = 0.032, P > 0.05). The number of days was positively correlated with the mean water temperature and negatively correlated with survey day (Table 7). Discussion In this study, we investigated the environmental characteristics of an irrigation pond and rice paddies with different management and histories, R. japonica breeding success, and how rice paddy environments were related to the breeding success. First, the PCA results showed that, in our study area, study sites were mainly characterized by environmental factors mainly controlled by common agricultural practices, irrigation and weed control, and aquatic thermal conditions (Fig. 2 ). Vegetation cover increased with time after rice paddy abandonment, but other than vegetation cover, there was no clear pattern of change over time, suggesting that the management of each site primarily influenced environmental factors. Second, our GAMM results showed that R. japonica spawned egg masses after rainfall, and when the air and water temperatures were relatively low. A previous study also noted the relationship between precipitation and breeding activities (Kuramoto and Ishikawa 2000 ), and in addition, our results suggested that low temperature and water temperature were key factors for egg mass spawning by R. japonica . Because R. japonica is adapted to cool climates, breeding activities occurred when temperatures were relatively low during the study period. Not only the preferred breeding habitat, but also the egg-rearing aquatic habitats in relation to water temperature, water depth, and vegetation cover, are linked to important agricultural practices in rice paddies, irrigation and weed control. Next, we discussed how each of them related to the reproductive success of R. japonica . Irrigation: water temperature and depth Rana japonica preferred open areas for breeding sites. These areas appeared to improve egg mass survivorship, because during winter when breeding occurs, the water temperature could decrease to the embryonic critical thermal limit (Kadowaki 2002 ); however, the surface water could simultaneously be warmed by the sun to a suitable temperature for embryo development. This explains why hatching success was related to the minimum water temperature; the higher the temperature, the higher the success rate was during the study period. Cool weather is preferred for breeding, and they spawn egg masses in shallow areas so that the water temperature does not become too cold for the embryos to survive and develop. However, the number of days to hatching increased when water temperature was relatively high. During the study period, water temperatures occasionally exceeded 25°C. Because the gelatinous material covering the egg mass can be heated by sunlight, the temperature within the egg mass in shallow water may rise considerably above that of the surrounding water (Kadowaki 2002 ). Thus, temperatures could increase to levels too high for embryonic development in R. japonica (critical thermal maximum for embryonic development is 29°C; Kuramoto et al. 1971 ). To maintain a water temperature range suitable for embryonic development, a slow water flow must be maintained through the aquatic habitat. In rice paddies, the water depth is typically low; therefore, water temperature is an important factor, especially in stagnant water. Our results indicated that egg mass survival was improved with a decrease in the number of days to hatch. There were fewer days to hatch for egg masses that spawned later during the study period; the egg masses found between 14 and 30 March all hatched between 30 March and 6 April (Table 2 ). When adult frogs choose breeding sites, they avoid aquatic habitats where egg masses have already been deposited, presumably because of the risk of predation or competition with larvae that previously hatched (Iwai et al. 2007 ). In future, the influence of egg mass density on the choice of breeding habitat, and how late-deposited egg masses catch up with the early-deposited egg masses should be studied. Practically, in cultivated rice paddies, it is better for egg masses to hatch earlier, because in April the bottom of the rice paddy is turned over and flattened by heavy machinery to prepare for rice seedling transplantation. Thus, it is difficult for larvae to survive this agricultural practice unless refugia are available. Aquatic habitats in fallow rice paddies could be safer egg-rearing habitat and provide a refuge for larvae. The relationship between hatching success and the water depth was not linear. If the water was very shallow, egg masses were at risk of drying; if the water level was deep, the water temperature could be lower than the suitable range for embryonic development. Furthermore, we found racoon ( Procyon lotor ) footprints at our study sites. A camera trap captured P. lotor , spot-billed ducks ( Anas zonorhyncha ), and mallards ( Anas platyrhynchos ) entering our study sites and foraging or paddling around them (Hiratsuka unpubl.). P. lotor is an invasive alien species in Japan, and their negative effects on anuran species have been reported in satoyama landscapes (Kuriyama et al. 2021 ); P. lotor was introduced in our study area in 2005, and since then the population has increased (Higashide et al. 2019 ). The decrease in the hatching success rate at a depth of approximately 4 cm (Fig. 3 ) could be explained by the effects of P. lotor ; however, more studies on P. lotor ’s foraging habits and distribution are required to evaluate their impact on egg masses. Osawa and Hayama ( 2000 ) reported that A. zonorhyncha consumed R. japonica egg masses. Based on the video captured by the camera trap, it was unclear whether the ducks predated the frog egg masses (Hiratsuka unpubl.), but they may have unintentionally kicked and scattered the egg masses while foraging in relatively deep water at our study sites. The hatching success rate decreased with increasing depth and was negatively correlated with water surface area. Duck foraging is more often observed in larger aquatic habitats; therefore, relatively small and shallow aquatic habitats could protect frog egg masses from ducks. By controlling the timing and amount of water flowing into the rice paddies, it is possible to create suitable breeding and egg-rearing habitat conditions for R. japonica . Weed control: vegetation cover During the breeding season, male frogs wait for female frogs in the water; therefore, vegetation could be an obstacle for males, thus, they appear to avoid aquatic areas with large amounts of vegetation (Kadowaki 2002 ). Additionally, our results showed that they also avoided areas with very low vegetation coverage. The vegetation at the study sites were mainly withered plant stems from the previous year. This vegetation could function as a hiding place for male frogs while they wait for female frogs, and they may also prevent egg masses from floating away. Weed plants spread in abandoned rice paddies (Kusumoto et al. 2005 ); therefore, to create a sustainable suitable breeding habitat for R. japonica , the water surface does not necessarily need to be cleared of weeds, but it is important to implement proper management practices to prevent weed overgrowth. Conclusion We found new egg masses in the IP, FTs, and RPs, but not in FFs, where vegetation was not managed and no pools of water were found. Our investigation revealed the relationship between R. japonica breeding success and various aspects of the aquatic habitat in rice paddies with various management histories. To increase the generalizability of the suitable environmental conditions of rice paddy as breeding and egg-rearing habitats for R. japonica , further investigations at multiple geographic locations are needed. Nevertheless, our study revealed the key aspects of aquatic environments associated with breeding site preference and hatching success of R. japonica , and how agricultural practices, irrigation and weed control, affect breeding success by alternating the aquatic environments. The agricultural practices are essential for rice cultivation, and at the same time, they can be practical measures to improve the rice paddy environments to create preferable breeding and egg-rearing habitat for R. japonica . Declarations Funding and Competing Interests The authors did not receive support from any organization for the submitted work. The authors have no competing interests to declare that are relevant to the content of this article. Author Contribution All authors contributed to the study conception and design. Material preparation and data collection were performed by Yuki Kimura and Motoshi Hiratsuka, and analysis was performed by Risa S. Naito. The first draft of the manuscript was written by Risa S. Naito and all authors commented on previous versions of the manuscript. All authors read and approved of the final manuscript. Acknowledgement We thank colleagues for helping collect data in the field. We also thank Dr. Masaru Sakai for helping to set up the data loggers and interpreting the logger data. The present study complies with the current laws of Japan in the collection and the use of animals in research and complies with the American Society of Ichthyologists and Herpetologists (ASIH) “Guidelines for Live Amphibians and Reptiles in Field and Laboratory Research” (https://bit.ly/ASIH_Herps). Data Availability The datasets analyzed during the current study are available from the corresponding author on reasonable request. References Fujioka M, Lane SJ (1997) The impact of changing irrigation practices in rice fields on frog populations of the Kanto Plain, Central Japan. Ecol Res 12:101-108 Goldingay RL, Newell DA (2005) Population estimation of the Green and golden bell frog Litoria aurea at Port Kembla. Aust J Zool 33:210-216 Gosner KL (1960) A simplified table for staging anuran embryos and larvae with notes on identification. 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Accessed 25 April 2024 Japan Meteorological Agency (2024) Weather statistics: an online reference. https://www.data.jma.go.jp/stats/etrn/index.php?prec_no=43&block_no=1070&year=&month=&day=&view=. Accessed 25 April 2024 Kadowaki M (2002) Environmental condition in breeding sites of Japanese brown frog, Rana (Rana) japonica Gunther: Especially the difference of water temperature among breeding spots. Jpn J Conserv Ecol 7:1-8 Karraker NE, Gibbs JP (2009) Amphibian production in forested landscapes in relation to wetland hydroperiod: A case study of vernal pools and beaver ponds. Biol Conserv 142:2293-2303 Katayama N, Baba YG, Kusumoto Y, Tanaka K (2015) A review of post-war changes in rice farming and biodiversity in Japan. Agric Syst 32:73–84 Kellner A, Green DM (1995) Age structure and age at maturity in Flower’s toad, Bufo woodhousii fowleri , at their northern range limit. J Herpetol 29:485-489 Kidera N, Kadoya T, Yamano H, Takamura N, Ogano D, Wakabayashi T, Takezawa M, Hasegawa M (2018) Hydrological effects of paddy improvement and abandonment on amphibian populations; long-term trends of the Japanese brown frog, Rana japonica . Biol Conserv 219:96-104 Kuramoto M, Ishikawa H (2000) Breeding ecology of brown frogs in Yamada park, Kitakyusyu, Japan. B Herpetol Soc Jpn 1:7-18 Kuramoto M, Sumida M, Saida M (1971) Embryonic temperature tolerance in brown frogs. B Herpetol Soc Jpn 4:1-4 Kuriyama T, Asazuma Y, Takagi S (2021) Range expansion and impact for native species of invasive racoons. Jpn J Environ Entomol and Zool 32:131-136 Kurniawan AH, Sato S, Cheng W, Dewi PK, Kobayashi K (2021) Animal abundance and soil properties affected by long-term organic farming in rice paddies in a typical Japanese yatsuda landscape. Environ Monitor Assess 193:273 Kusumoto T, Ohkura T, Ide M (2005) The relationships between the management history and vegetation types of fallow paddy field and abandoned paddy fields; case study of Sakuragawa and Kokaigawa river basin in Ibaraki prefecture. J Rural Planning 24:7-12 Lawler SP (2001) Rice fields as temporary wetlands: A review. Isr J Zool 47:513-528 Matsushima N, Ikari T, Adachi M, Nishihiro J (2023) Use of artificial spawning pools by the Japanese brown frog, Rana japonica , in wet abandoned paddies of Inazi City, Chiba. Jpn J Conserv Ecol 28:467-472 Matsui M, Maeda N (2018) Encyclopedia of Japanese frogs. Bun-Ichi Sogo Shuppan Co. Ltd, Chiyoda-ku, Tokyo Matsui M, Mori A (ed) (2021) Amphibians and Reptiles of Japan, 2nd edn. Sunrise Shuppan, Shiga Ministry of Environment, Japan (2024) The Red List of threatened species: prefecture level. https://ikilog.biodic.go.jp/Rdb/pref. Accessed 25 April 2024 Morimoto Y (2011) What is Satoyama? Points for discussion on its future direction. Landscape and Ecol Eng 7:163-171 Moriyama H (1997) What does it mean to protect paddy fields? Rural Culture Association, Saitama Naito SN, Hiratsuka M, Ichihara R (2025) Frog assemblage patterns in a small-scaled traditional rice paddy ( yatsuda ) area in Japan. Community Ecol 26:501-508 Osawa S, Shimada M, Katsuno T (2005) Environmental factors that regulate the density of Rana porosa porosa on the levees of flatland paddy fields. J Rural Planning Assoc 24:91-102 Osawa S, Katsuno T (2002) Environmental Factors Influencing the Relative Abundance of Brown Frogs in Urban Area Ecological Parks. J Jpn I Landscape Archit 65:513-516 Osawa S, Hayama Y (2000) The note of frogspawn and tadpole eating by rescued wild animals. B Herpetol Soc Jpn 2:81-84 Pearl CA, Adams MJ, Leuthold N, Bury RB (2005) Amphibian occurrence and aquatic invaders in a changing landscape: implications for wetland mitigation in the Willamette valley, Oregon, USA. Wetlands 25:76-88 R Development Core Team (2024) R: A language and environment for statistical computing, Version 4.4.3. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org Rudolf VHW, Rodel M-O (2005) Oviposition site selection in a complex and variable environment: the role of habitat quality and conspecific cues. Oecologia 142:316-325 Snodgrass JW, Komoroski MJ, Bryan AL, Burger J (2000) Relationships among isolated wetland size, hydroperiod, and amphibian species richness: implications for wetland regulations. Conserv Biol 14:414-419 Tomioka K (2000) Long-term dynamics of breeding activity of two brown frogs Rana japonica and R. ornativentris in a bottomland rice paddies in the northern Kanto Plain, Japan. J Nat Hist Museum I, Chiba. Special Issue 3:9-16 Uchiyama R (2005) Tanbonoikimono-zukan, Yama-kei Publishers Co., Ltd., Chiyoda-ku, Tokyo Uematsu Y, Koga T, Mitsuhashi H, Ushimaru A (2010) Abandonment and intensified use of agricultural land decrease habitat of rare herbs in semi-natural grassland. Agr Ecosyst Environ 135:304–309 Washitani I (2001) Traditional Sustainable Ecosystem ‘SATOYAMA’ and Biodiversity Crisis in Japan: Conservation Ecological Perspective. Global Environ Res 5:119–133 Yamazaki F (1996) A story of rice paddy. Rural Culture Association, Saitama Zheng X, Natuhara Y, Zhong S (2021) Influence of midsummer drainage and agricultural modernization on the survival of Zhangixalus arboreus tadpoles in Japanese paddy fields. Environ Sci Pollut Res 28:18294-18299 Tables Table 1. Number of new egg masses of Rana japonica found at each study site during each survey between 14 and 30 March 2023. PI UP FF FT RP Date PI UP1 UP2 UP3 UP4 FF1 FF2 FF3 FT1 FT2 FT3 RP1 RP2 RP3 14-Mar 4 2 0 0 0 0 0 0 0 0 0 0 0 2 16-Mar 2 0 0 0 0 0 0 0 0 0 0 0 0 0 19-Mar 0 16 15 0 3 0 0 0 0 5 11 2 3 10 20-Mar 0 1 0 0 1 0 0 0 11 0 0 0 0 1 23-Mar 2 0 0 0 0 0 0 0 0 0 0 0 1 0 27-Mar 0 2 0 0 0 0 0 0 0 0 3 0 4 3 30-Mar 7 0 0 0 0 0 0 0 0 1 1 0 1 0 sum 5 21 15 0 4 0 0 0 11 6 15 2 9 16 IP, irrigation pond; UP, upstream rice paddies; FF, rice paddies fallow for five years; FT, rice paddies fallow for two years; RP, actively cultivated rice paddies. No egg masses were found before 14 March 2023 and after 30 March 2023. Table 2. Summary data of Rana japonica egg masses surveyed in each site category Category Total No. of egg masses a Mean depth new egg masses b (cm) Dates new egg masses were found c Hatching success rate (%) Mean depth between the first day and the day egg masses hatched or died d (cm) Date range when completely hatched or died e No. of days to hatch f IP 35 12.8 ± 0.5 14–30 March n/a n/a n/a n/a URs 40 3.7 ± 0.5 14–27 March 93 3.4 ± 0.3 30 March –6 April 14.9 ± 0.7 FFs 0 n/a n/a n/a n/a n/a n/a FTs 32 3.7 ± 0.4 19–30 March 78 3.8 ± 0.3 30 March –3 April 11.6 ± 0.5 RPs 27 6.4 ± 0.5 14–30 March 85 5.3 ± 0.4 30 March –6 April 11.6 ± 0.5 IP, irrigation pond; UPs, upstream rice paddies; FFs, rice paddies fallow for five years; FTs, rice paddies fallow for two years; RPs, cultivated rice paddies; n/a, not applicable. a The total number of egg masses found b Mean ± standard error (SE) of the water depth where each new egg mass was found c The time period during which new egg masses were found d Mean depth of each egg mass between the first day and the day an egg mass was found e The day egg masses were confirmed to have hatched or died f Mean ± SE of the number of days it took for each egg mass to hatch. Table 3. Summary of environmental factors for each category Category Mean temperature (°C) Mean water temperature (°C) Mean minimum daily water temperature (°C) Mean solar radiation a (kW/m 2 ) Vegetation cover (%) Water surface area (m 2 ) IP 11.5 ± 0.2 10.2 ± 0.0 9.7 ± 0.3 6244 ± 28 3.0 224.0 URs 11.6 ± 0.1 13.3 ± 0.2 7.9 ± 0.6 5954 ± 53 55.9 ± 9.3 14.8 ± 7.9 FFs FF1: 10.6 ± 0.1 FF1: 8.8 ± 0.3 6110 ± 47 100 ± 0 0 FTs FT2: 13.4 ± 0.1 FT2: 8.9 ± 0.5 6394 ± 49 6.7 ± 1.2 95.7 ± 88.7 FT3: 14.8 ± 0.1 FT3: 11.3 ± 0.4 RPs RP1: 10.3 ± 0.1 RP1: 8.7 ± 0.4 1572 ± 241 5.0 ± 0 227.4 ± 16.1 RP3: 13.8 ± 0.1 RP3: 10.9 ± 0.3 IP, irrigation pond; UPs, upstream rice paddies; FFs, rice paddies fallow for five years; FTs, rice paddies fallow for two years; RPs, actively cultivated rice paddies. a Solar radiation between the day before the first new egg mass was found (11 March 2023) and the day all egg masses had completely hatched (6 April 2023). Table 4. The results of principal component analysis (PCA). Principal component 1 2 3 4 WTEMP (°C) -0.28 0.62 -0.16 -0.19 L_WTEMP (°C) 0.49 0.20 -0.02 -0.71 H_WTEMP (°C) -0.36 0.56 -0.04 0.27 SUN (kWh/m 2 ) -0.21 -0.23 -0.92 -0.18 VEG (%) -0.47 -0.45 0.17 -0.10 DEP (cm) 0.53 0.03 -0.31 0.58 Standard deviation 1.58 1.41 0.95 0.79 Proportion of Variance 0.42 0.33 0.15 0.10 Cumulative Proportion 0.42 0.75 0.90 1.00 The variables used for the analysis were the environmental factors measured during the study period at each study site group (irrigation pond, upper rice paddies, rice paddies fallow for two years, rice paddies fallow for five years, and actively cultivated rice paddies). H_WTEMP, mean maximum daily water temperature; WTEMP, mean water temperature; L_WTEMP, mean minimum daily water temperature; SUN, mean solar radiation mean water DEP, depth; VEG, proportion of water surface covered by vegetation Table 5. Summary of generalized additive mixed model analysis for breeding site preference. We constructed a model for the number of new Rana japonica egg masses found at each study site ( n = 134). Explanatory variable Estimate z value P -value (Intercept) 7.51 2.26 <0.05 RAIN 0.06 2.98 <0.01 TEMP −0.58 −3.19 <0.01 WTEMP −0.12 −0.63 0.53 L_WTEMP −0.59 −3.65 <0.001 SUN 0.06 0.35 0.72 DEP −0.14 −1.96 <0.05 VEG 0.04 3.22 <0.01 The explanatory variables of the model were the mean of the following environmental factors between the previous study day and the day before the study day: RAIN, precipitation; TEMP, temperature; WTEMP, water temperature; L_WTEMP, minimum daily water temperature; SUN, solar radiation; DEP, water depth where new egg masses were found; VEG, proportion of water surface covered by vegetation. Survey day was included in the models as a smooth term (edf = 1.1, Chi.sq = 7.59, P < 0.01). The log of water surface area was included as an offset term, and the categorical variable of site type was included as a random intercept. Table 6. Summary of generalized additive mixed model analysis for hatching success. We constructed a model for the success or failure of each Rana japonica egg mass to completely hatch ( n = 93). Explanatory variable Estimate z value P -value (Intercept) −61.55 −2.67 <0.05 L_WTEMP 7.87 2.86 <0.01 DAY −0.58 −1.49 0.14 AREA −0.07 −2.71 <0.05 The explanatory variables of the model were the mean of the following environmental factors between the first day an egg mass was found and the day it was confirmed to have hatched or died: L_WTEMP, minimum daily water temperature; DAY, survey day; AREA, water surface area. Mean water depth was included in the models as a smooth term (edf = 6.1, Chi.sq = 17.05, P < 0.05), and the categorical variable of site type was included as a random intercept. Table 7. Summary of generalized additive mixed model analysis for number of days to hatch. We constructed a model for the number of days it took each Rana japonica egg mass to hatch ( n = 81). Explanatory variable Estimate z value P-value (Intercept) −2.92 −2.10 0.04 WTEMP 0.69 6.12 <0.001 L_WTEMP −0.32 −1.95 0.05 DAY −0.11 −5.65 <0.001 AREA 0.00 −0.48 0.63 The explanatory variables of the model were the mean of the following environmental factors between the first day an egg mass was found and the day complete hatching was confirmed: WTEMP, water temperature; L_WTEMP, minimum daily water temperature; DAY, survey day; AREA, water surface area. Mean water depth was included in the models as a smooth term (edf = 1, Chi.sq = 0.032, P > 0.05) and categorical variable of site type was included as a random intercept. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 15 Apr, 2026 Reviews received at journal 15 Apr, 2026 Reviews received at journal 08 Apr, 2026 Reviewers agreed at journal 19 Mar, 2026 Reviewers agreed at journal 19 Mar, 2026 Reviewers invited by journal 16 Mar, 2026 Editor assigned by journal 16 Mar, 2026 Submission checks completed at journal 16 Mar, 2026 First submitted to journal 15 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-9126504","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":607120882,"identity":"a4a17b05-7923-4a51-8a3a-4c6d6d2183cc","order_by":0,"name":"Risa S. Naito","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABBklEQVRIiWNgGAWjYDACZgjFAyI+MLAlyIEYBx4QowWoh3EGUIsxWEsCMbbBtCQ2gHj4tJi3sz/8wLjDTsaevYGx6UZZWvr8sMMPgbbYyek2YNcic5jHWILxTDIPD88Bxuacczm5G2+nGQC1JBubHcCuRYKZh0GCsY2Zh0cigf1xbltF7sbZCSAtBxK34dTC/vgHY1s9SAtjM1BLuuHs9A8EtDCYAW05DNOSkyAvnUPIFh4zi8S24zw8Zw42Av2SZrhBOqfgQIIBHr/wH39842NbtT17e/PB5pyyZHn52embP3yosJPDpQUMEsAkYwOYMgCrNMCjHAPIN5CiehSMglEwCkYCAADDDljQzEeEtgAAAABJRU5ErkJggg==","orcid":"","institution":"Waseda University","correspondingAuthor":true,"prefix":"","firstName":"Risa","middleName":"S.","lastName":"Naito","suffix":""},{"id":607120883,"identity":"6c86652b-5a47-4aed-aab7-0ac76c871ca4","order_by":1,"name":"Yuki Kimura","email":"","orcid":"","institution":"Waseda University","correspondingAuthor":false,"prefix":"","firstName":"Yuki","middleName":"","lastName":"Kimura","suffix":""},{"id":607120884,"identity":"ce804bf5-758c-4f1d-a849-502395622f7d","order_by":2,"name":"Motoshi Hiratsuka","email":"","orcid":"","institution":"Waseda University","correspondingAuthor":false,"prefix":"","firstName":"Motoshi","middleName":"","lastName":"Hiratsuka","suffix":""}],"badges":[],"createdAt":"2026-03-15 06:08:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9126504/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9126504/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104995962,"identity":"9c2106c3-2d71-4504-a418-dae25b0983df","added_by":"auto","created_at":"2026-03-19 16:10:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1009200,"visible":true,"origin":"","legend":"\u003cp\u003eAerial photograph of the study area. Irrigation pond (IP), upper rice paddies managed to restore the wetland ecosystem (UR1–UR3), middle rice paddies fallow for five years (FF1–FF3), downstream rice paddies fallow for two years (FT1–FT3), and cultivated rice paddies (RP1–RP3). All study sites were in the yatsuda wetland area (upper left) in Japan (upper right). Zoomed in photographs of each site category are in the bottom panels.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9126504/v1/93754d61cad3866f0ff5e4f3.png"},{"id":104995992,"identity":"344367cf-87ea-41ff-add0-5cf641683bfa","added_by":"auto","created_at":"2026-03-19 16:11:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":71394,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal component analysis (PCA) biplot graph representing study site groups. Two main principal components (PC1 and PC2) are shown for the following environmental factors: H_WTEMP, mean maximum daily water temperature (°C); WTEMP, mean water temperature (°C); L_WTEMP, mean minimum daily water temperature (°C); SUN, mean solar radiation (kWh/m\u003csup\u003e2\u003c/sup\u003e); DEP, mean water depth (cm); and VEG, proportion of water surface covered by vegetation (%). PC1 and PC2 explained 42% and 33% of the variance, respectively. Vector direction and length indicate each environmental factor’s contribution to the first two components in the PCA. IP, irrigation pond; URs, upper rice paddies; FTs, rice paddies fallow for two years; FFs, rice paddies fallow for five years; RPs, actively cultivated rice paddies.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9126504/v1/070e17cd517fdbc5acee51bd.png"},{"id":104995901,"identity":"a496d3b4-5397-49fd-9ba5-21080c8f7991","added_by":"auto","created_at":"2026-03-19 16:10:39","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":40233,"visible":true,"origin":"","legend":"\u003cp\u003ePartial effects of mean water depth (between the first day each egg mass was found and the day complete hatching or death was confirmed) on \u003cem\u003eRana japonica\u003c/em\u003e egg mass hatching success in the irrigation pond and rice paddies estimated by generalized additive models. We constructed a model for each egg mass. Dotted lines show the 95% confidence interval around the smooth terms. Whiskers on the \u003cem\u003ex\u003c/em\u003e-axis show the predictor variable locations.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9126504/v1/cc68f4ea2176f8cd50eb13f7.png"},{"id":105035126,"identity":"b7250303-f271-4378-8d06-f057e7c93ddc","added_by":"auto","created_at":"2026-03-20 07:25:32","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1845506,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9126504/v1/9d0d6d96-bec0-431a-b4d9-9731aa869ad2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Agricultural practices improve breeding success of indigenous frogs in restored rice paddies: A case study from the Miyajima Wetland, Japan","fulltext":[{"header":"Introduction","content":"\u003cp\u003eRice paddies and associated areas, such as irrigation ponds and secondary forests, are typically connected via irrigation channels (Washitani \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2001\u003c/span\u003e) and play an essential role as substitute habitats for wetland species (Lawler \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). Rice paddy ecosystems have been established over the long history of rice cultivation in Japan (Yamazaki 2005); however, since the 1950s, the modernization of rice paddies, including land consolidation projects, led to the degradation of rice paddies as habitats for wetland species (Natuhara 2013; Katayama et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), and many common species in these areas, such as frogs, are now endangered (Hasegawa et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Japan Integrated Biodiversity Information System \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Moreover, as the population of farmers has aged, more rice paddies have been abandoned and have dried out and lost their function as habitat for wetland species (Fujioka and Lane \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Uematsu et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2010\u003c/span\u003e; Katayama et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo create suitable habitats for wetland species under these circumstances, the restoration of wetland environments and resumption of agricultural practices of rice paddies have been suggested, however their effects have not been well studied (Kidera et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Matsushima et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In addition to the basic knowledge of the life histories of wetland species, a better understanding of the relationship between the life histories, environmental factors, and agricultural practices is required to develop practical restoration measures. In terms of suitability as restoration sites, modernized rice paddies have reduced functions as habitats for wetland species, whereas traditional rice paddies remaining in small-scale arable land in small valleys (called \u0026ldquo;yatsuda\u0026rdquo;) (Kurniawan et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) exhibit high restorative potential as a wetland environment, because some yatsuda and associated areas have preserved various lentic habitats with high connectivity (Kidera et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Naito et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eYatsuda are also being abandoned because of the aging farming population (Katayama et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), but the changes in environmental factors after abandonment are still not well understood. To develop effective conservation measures for wetland species, we must investigate how environmental factors change after agricultural practices are ceased. In this study, we focused on frogs found in rice paddies, as they are representative species in rice paddy ecosystems (Moriyama \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). Because frogs need stable aquatic habitats for their egg and larval life stages (Snodgrass et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Pearl et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Karraker and Gibbs \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), understanding how various abiotic and biotic aquatic environmental factors affect their reproductive success is essential for sustaining their populations (Rudolf and Rodel \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). A comprehensive study of the relationship between environmental factors and reproductive success of frogs in spatiotemporally heterogeneous inundated habitats (Kellner and Green \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1995\u003c/span\u003e; Goldingay and Newell \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), and how aquatic habitats vary depending on rice paddy management, are essential for understanding the interaction between agricultural practices and frog population dynamics.\u003c/p\u003e \u003cp\u003eWe conducted our study at a yatsuda area in the Mikajima Wetland, where we found frog assemblages in restored rice paddies with various management histories and irrigation ponds (Naito et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2025\u003c/span\u003e); thus, multiple types of lentic habitats were available as study sites. In this study, we aimed to determine how environmental factors differ among rice paddies with different management histories and irrigation ponds, and how do environmental factors influence the breeding success of indigenous frog species. Specifically, we examined four groups of study sites consisting of rice paddies actively cultivated, fallow for two and five years, and an irrigation pond. We evaluated preferred breeding habitat conditions, egg survival, and the number of days to hatching to assess reproductive success. Finally, we discussed how rice paddy environments differ by management histories and how agricultural practices influence the reproductive success of \u003cem\u003eR. japonica\u003c/em\u003e by altering rice paddy environments.\u003c/p\u003e"},{"header":"Methodology","content":"\u003cp\u003eStudy area: This study was conducted in the Mikajima Wetland in the Sayama Hills, Tokorozawa City, Saitama Prefecture. The Sayama Hills cover approximately 3500 ha of forested and agricultural land and belong to six municipalities in Saitama Prefecture and the Tokyo metropolitan area. The satoyama landscape (socio-ecological production landscape) (Morimoto \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) in this area, which includes the yatsuda areas, has been maintained and conserved by local people and the government, despite its proximity to Tokyo. Historically, a part of the Mikajima Wetland was converted to yatsuda and managed by farmers. The yatsuda and wetland areas together supported the wetland species.\u003c/p\u003e \u003cp\u003eOur study area was in one of the yatsuda areas in the Mikajima Wetland. No land consolidation and improvement projects have been conducted in the study area, and the slopes surrounding the yatsuda area are primarily covered by secondary forests and grasslands. Over a 10-year period from 2014 to 2023, the mean annual precipitation and temperature in the area were 1519 mm and 15.1\u0026deg;C, respectively (Japan Meteorological Agency \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Farmers managed rice production in the area until they abandoned the rice paddies in 1970s, and thereafter, Waseda University and Saitama Midori-no-Mori Nature Park managed this area to conserve the wetland ecosystem. In the Waseda University-managed area, as one of the conservation measures for wetland ecosystem, four rice paddies were restored in 2002, three were restored in 2008, 2009, and 2010, and they were rotationally cultivated except the first group restored in 2002. The second group, which included three rice paddies restored in 2008, was cultivated from 2013\u0026ndash;2015, the third group (restored in 2009) was cultivated from 2016\u0026ndash;2018, and the fourth group (restored in 2010) was cultivated from 2019\u0026ndash;2021; the second group was then cultivated again in 2022. We chose these 13 rice paddies as our study sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The first group of rice paddies was located upstream of the remaining paddies; therefore, they were referred to as upper rice paddies (UR1\u0026ndash;UR4). The other rice paddies recently underwent cultivation in 2016\u0026ndash;2018, 2019\u0026ndash;2021, and 2022\u0026ndash;present, and thus, were referred to as follows: rice paddies fallow for two years (FT1\u0026ndash;FT3), rice paddies fallow for five years (FF1\u0026ndash;FF3), and actively cultivated rice paddies (RP1\u0026ndash;RP3) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Owing to the lack of land consolidation and improvement projects, all paddies remained wet because of water flow and seepage from the surrounding environments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eOne irrigation pond (IP) connected to the rice paddies by the Sunagawa River was also investigated in this study (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The IP was included in our study sites because it is a common feature in yatsuda areas and is an important aquatic habitat for wetland species. The IP was surrounded by forest with deciduous trees (Konara Oak [\u003cem\u003eQuercus serrata\u003c/em\u003e] and Japanese Snowbell [\u003cem\u003eStyrax japonicus\u003c/em\u003e]), and the branches covered parts of the water surfaces. The IP was located at the uppermost part of the Sunagawa River and the Sunagawa River supplied water to all paddies, except the UR1\u0026ndash;UR4. Water in FT1\u0026ndash;FT3 flowed down to FF1\u0026ndash;FF3 and subsequently to a downstream reed field. Water from RP1\u0026ndash;RP3 also flowed into the reed fields.\u003c/p\u003e \u003cp\u003eThe water levels of RP1\u0026ndash;RP3 decreased to a few centimeters during the transplanting period between May and June, and the harvesting period in September, but generally remained inundated throughout the year. All paddies were surrounded by vegetated levees that were 1\u0026ndash;2 m wide and 50\u0026ndash;70 cm high. The riparian vegetation was mowed to a height of several centimeters two or three times a year. The predominant vegetation in the UR1\u0026ndash;UR4 and FT1\u0026ndash;FT3 were common reeds (\u003cem\u003ePhragmites australis\u003c/em\u003e), but the FT1\u0026ndash;FT3 also contained Hera-omodaka (\u003cem\u003eAlisma canaliculatum\u003c/em\u003e) and Konagi (\u003cem\u003eMonochoria vaginalis\u003c/em\u003e), which are common species found in rice paddies in Japan.\u003c/p\u003e \u003cp\u003eStudy species: Japanese brown frog (\u003cem\u003eRana japonica\u003c/em\u003e)\u003c/p\u003e \u003cp\u003eWe chose \u003cem\u003eR. japonica\u003c/em\u003e for this study because it is a common species in yatsuda areas, but its population has been decreasing (Tomioka \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Osawa and Katsuno \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Zheng et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This species originates in the north so adapted to cool climates (Kuramoto et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). Breeding occurs from January to March in still water, and metamorphosis occurs from May to June (Matsui and Maeda, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). One female frog spawn one egg mass containing 500\u0026ndash;3000 eggs during a breeding season (Matsui and Mori \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This species prefers open areas as breeding sites because vegetation covering the water surface interferes with breeding behavior (Kadowaki \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). The critical thermal maximum of their embryos is 33\u0026deg;C, and the critical thermal minimum is slightly higher than 4\u0026deg;C; for development, the highest temperature the embryos can withstand is 29\u0026deg;C and the lowest is also slightly higher than 4\u0026deg;C (Kuramoto et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). \u003cem\u003eR. japonica\u003c/em\u003e spends its non-breeding season in the secondary forest surrounding the rice paddies (Matsushima et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The body lengths (snout-to-vent) of mature males and females are 34\u0026ndash;63 mm and 43\u0026ndash;67 mm, respectively (Matsui and Mori \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). This species is included in the list of 31 prefecture-level endangered species (Ministry of Environment, Japan \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eField survey\u003c/p\u003e \u003cp\u003eEnvironmental factors: We placed data loggers (Tidbit v2, Onset Computer Corporation, Bourne, MA, USA) in the IP, and rice paddies (UR4, FF1, FT2, FT3, RP1, and RP3) where the water level was sufficiently deep to install loggers and record the water temperature every 30 min during the survey period. We set two data loggers approximately 1 m aboveground, one near the IP, and one in FF1, to record the air temperature every 30 min during the survey period. We obtained precipitation data for Tokorozawa City for the study period from the Japan Meteorological Agency (Japan Meteorological Agency \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). We recorded the amount of water surface covered by vegetation based on visual observation for each study site and calculated the water surface area of each study site using ArcGIS (version 10.8; ESRI Inc., Redlands, California, USA) based on an aerial photograph taken by an unmanned aerial vehicle (Phantom 4 Pro V2.0 DJI, Guangdong, China) on 12 May 2023. We obtained the point solar radiation in the middle of each study site using ArcGIS with a 5-m mesh digital elevation model (Geospatial Information Authority of Japan 2023).\u003c/p\u003e \u003cp\u003eEgg masses: We walked a circuit of levees and banks at each site and numbered all egg masses found. We prepared a map of each study site based on the aerial photograph taken on 12 May 2023 and recorded the location of each egg mass. To avoid double counting, we referred to the developmental stage table described by Gosner (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1960\u003c/span\u003e) and checked the developmental stage of each egg mass to ensure that it was newly spawned. For each egg mass, we recorded the species (Uchiyama \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), water depth (measured manually with a folding ruler), and condition (hatched, dead, or lost). When \u0026gt;\u0026thinsp;90% of the eggs in an egg mass hatched or died, we considered the egg mass to be hatched or dead. When we could not find an egg mass once we returned to its recorded location, we considered the egg mass lost. We conducted surveys every two or three days between 10:00 and 14:00 from 17 February to 10 April 2023 (18 total surveys).\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eWe conducted principal component analysis (PCA) of the main environmental factors characterizing each study site group to investigate how environmental factors vary among rice paddies with different management histories and irrigation ponds. We used the following environmental factors for the analysis: vegetation cover and the mean values of maximum daily water temperature, water temperature, minimum daily water temperature, solar radiation, and water depth during the study period. Statistical analyses were performed using R software (version 4.3.3; R Development Core Team \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo determine \u003cem\u003eR. japonica\u003c/em\u003e\u0026rsquo;s preferred environment for breeding and egg-rearing habitats, we constructed three generalized additive mixed models (GAMMs) for (1) the number of newly found egg masses, (2) the hatching success of each egg mass, and (3) the number of days each egg mass took to hatch successfully. The response variable for (1) was the mean number of new egg masses found at each study site in a day divided by the number of days between the previous and current days. For (2) and (3) the response variables were the hatching success of each egg mass and the number of days each egg mass took to hatch successfully, respectively.\u003c/p\u003e \u003cp\u003eThe candidate explanatory variables for (1) were vegetation cover and the mean values of the following environmental factors between the previous survey day and the day before the survey: precipitation, temperature, minimum daily temperature, water temperature, minimum daily water temperature, solar radiation, water depth at the location where a new egg mass was found, and vegetation cover. These means were used because frogs typically spawn at night, while our surveys were conducted during the day. For (2), the candidate explanatory variables were survey day (number of days since egg masses were first observed in the study area, March 14), vegetation cover, water surface area and the mean values of environmental factors between the day an egg mass was first detected and the day it was confirmed to have completely hatched or died: water temperature, minimum daily water temperature and solar radiation. For (3), the candidate explanatory variables were survey day, vegetation cover, water surface area and the mean values of environmental factors between the day the first egg mass was detected and the day it was confirmed to have completely hatched: water temperature, minimum daily water temperature and solar radiation. Air and water temperature data were obtained from the data logger installed closest to each study site.\u003c/p\u003e \u003cp\u003eFor each model, Pearson\u0026rsquo;s correlation analysis was used to assess correlations among continuous environmental variables. Variables with strong correlation (\u003cem\u003er\u003c/em\u003e\u0026thinsp;\u0026ge;\u0026thinsp;0.6) were excluded from candidate explanatory variables to avoid strong multicollinearity. We set the error structure of the response variable as Poisson with log link function for model (1) and (3), whereas binominal with a logit link function for model (2). The log of the water surface area was included as an offset term in model (1). To account for potential nonlinear relationships between response and explanatory variables, the following factors were included in models as smooth terms: survey day in model (1), the mean water depth in model (2) and (3). In all models, study site group was included as a random intercept because observations within the same site category were expected to be more similar than those for different site categories. Statistical analyses were performed using the \u0026ldquo;gamm4\u0026rdquo; package in R. Statistical significance was set at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cp\u003eField survey\u003c/p\u003e\n\u003cp\u003eEnvironmental factors:It rained on 10 of the 27 days\u0026nbsp;between the day before the first egg mass was found (11 March) and day when all egg masses\u0026nbsp;had hatched, died, or been lost (6 April). During this time, the study area received 3.5 ± 1.2 mm (range, 0–22 mm) of precipitation per day.\u003c/p\u003e\n\u003cp\u003eThe mean ± standard error (SE) and the minimum and maximum temperature in the study area between 11 March\u0026nbsp;and\u0026nbsp;6 April\u0026nbsp;were 11.47 ± 0.15\u0026nbsp;°C (range, 0.08–27.1 °C) and 11.50 ± 0.14 °C (range, 0.33–23.62 °C), respectively (Table 3). The mean temperatures were similar, but the temperature range was greater at the\u0026nbsp;IP.\u003c/p\u003e\n\u003cp\u003eThe mean ± SE and the minimum and maximum water temperature at IP, UP4, FF1, FT2, FT3, RP1, and RP3 sites between 11 March\u0026nbsp;and\u0026nbsp;6 April\u0026nbsp;were 10.23 ± 0.04\u0026nbsp;°C (range, 7.77–12.80 °C), 13.27 ± 0.15 °C (range, 2.40–29.7 °C), 10.60 ± 0.05 °C (range, 5.57–14.24 °C), 13.44 ± 0.12 °C (range, 4.32–26.01 °C), 14.83 ± 0.10 °C (range, 7.92–24.48 °C), 10.28 ± 0.06 °C (range, 4.38–19.32 °C), and 13.75 ± 0.08 °C (range, 7.59–23.35 °C), respectively. There were various thermal environments\u0026nbsp;in the study area.\u003c/p\u003e\n\u003cp\u003eWe calculated\u0026nbsp;the solar radiation,\u0026nbsp;water surface\u0026nbsp;area\u0026nbsp;(AREA),\u0026nbsp;and vegetation cover for each study site. The mean ± SE of solar radiation between 11 March\u0026nbsp;and\u0026nbsp;6 April\u0026nbsp;in each study site group were 6244 ± 28, 5954 ± 53, 6110 ± 47, 6394 ± 49, and 1572 ± 241 kWh/m\u003csup\u003e2\u003c/sup\u003e, respectively. The area was the largest at FF3 (273.0 m\u003csup\u003e2\u003c/sup\u003e) and smallest at UR4A (2.5 m\u003csup\u003e2\u003c/sup\u003e). The mean ± SE of the water surface area and vegetation cover of each study site group were as follows: IP, 224 m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eand 3%; URs, 14.8 ± 7.9 m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eand 55.9 ± 9.3%; FFs, 0 m\u003csup\u003e2\u003c/sup\u003e and 100 ± 0%; FTs, 95.7 ± 88.7 m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eand 6.7 ± 1.2%; RPs, 227.4 ± 16.1 m\u003csup\u003e2\u003c/sup\u003e, and 5 ± 0% (Table 3). No surface water was observed in the FFs during the study period; consequently, no egg masses were found.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEgg masses: During the 18 surveys conducted over the study period, we found 134 egg masses of \u003cem\u003eR. japonica\u003c/em\u003e and nine egg masses (six in FTs and three in RPs) of the Montane brown frog (\u003cem\u003eR. \u003cem\u003eornativentris)\u003c/em\u003e\u003c/em\u003e. New \u003cem\u003eR. japonica\u003c/em\u003e egg masses were recorded from 14–30 March at all study sites,\u0026nbsp;except UR3 and FF1–FF3 (Table 1). A \u003cem\u003eJapanese common toad (Bufo japonicus formosus Boulenger, 1883) spawning event occurred between 27 and 30 March at\u0026nbsp;\u003c/em\u003e\u003cem\u003ethe IP\u003c/em\u003e\u003cem\u003e; subsequently, the number of B. japonicus egg masses did not appear to increase, and they were not found at any other sites.\u0026nbsp;\u003c/em\u003eThe numbers of \u003cem\u003eR. japonica\u003c/em\u003e egg masses and the mean ± SE of water depth at which each egg mass was found were as follows: IP, 35 at 12.8 ± 0.5 cm; URs, 40 at 3.7 ± 0.5 cm; FFs, 0; FTs, 32 at 3.7 ± 0.4 cm; and RPs, 27 at 6.4 ± 0.5 cm (Table 2). Because there were very few \u003cem\u003eR. \u003cem\u003eornativentris\u003c/em\u003e\u003c/em\u003e and \u003cem\u003eB. japonicus\u003c/em\u003e egg masses compared with that of \u003cem\u003eR. japonica\u003c/em\u003e, we assumed that interspecific interactions had little influence on \u003cem\u003eR. japonica\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003eEgg mass hatching: The hatched proportion of each egg mass was recorded at each survey until all egg masses had hatched or died. We found completely hatched egg masses in the study area on 27 March\u0026nbsp;at RP3 and 6 April\u0026nbsp;at UR1, FT1, FT3, RP2, and RP3. However, we lost all 35 egg masses in\u0026nbsp;the IP, because the egg masses moved to the deep area of\u0026nbsp;the IP, and\u0026nbsp;two and four in FT3 and RP3, respectively, because the egg masses moved\u0026nbsp;to\u0026nbsp;the middle of\u0026nbsp;the\u0026nbsp;rice paddies, thus, we were unable to observe them. We tracked 93 egg masses from the day they were\u0026nbsp;deposited to the day they\u0026nbsp;completely hatched or died. We found 12 dead egg masses; three in UR4 were floating on the water surface, one in FT2 and six in FT3 were broken and scattered, two in RP2 were brown in color and displayed no further development, and two in RP3 were desiccated. The overall hatching success rate was 87%. The mean ± SE of days each egg mass took to completely hatch were 14.9 ± 0.7, 11.6 ± 0.5, and 11.6 ± 0.55 days in the URs, FTs, and PRs, respectively (Table 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStatistical analysis\u003c/p\u003e\n\u003cp\u003eThe\u0026nbsp;PCA results showed that our study site groups were\u0026nbsp;mainly characterized by two principal components (PC1 and PC2) (Table 4). PC1 was positively correlated with the\u0026nbsp;mean values of water depth and\u0026nbsp;minimum daily water temperature\u0026nbsp;and negatively correlated with vegetation cover. PC2 was positively correlated with the\u0026nbsp;mean values of water temperature\u0026nbsp;and\u0026nbsp;maximum daily water temperature. PC1 and PC2 accounted for 42% and 33% of the variance, respectively. PC1 was associated with the factors mainly controlled by agricultural\u0026nbsp;practices and PC2 was associated with aquatic\u0026nbsp;thermal environment conditions (Fig. 2).\u003c/p\u003e\n\u003cp\u003eModel analysis\u003c/p\u003e\n\u003cp\u003e(1) Preferred breeding sites:Based on the Pearson’s coefficient values, we excluded\u0026nbsp;the mean minimum daily water temperature\u0026nbsp;from the explanatory variables. We constructed a GAMM with\u0026nbsp;the mean number of new egg masses\u0026nbsp;as the response variable\u0026nbsp;and vegetation cover\u0026nbsp;and the mean values of\u0026nbsp;precipitation, temperature, water temperature, minimum daily temperature, solar radiation, and water depth (at which new egg masses were found) as explanatory variables (\u003cem\u003en\u003c/em\u003e = 134). The smooth term estimated for the number of days was statistically significant (edf = 1.1, Chi.sq = 7.59,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026lt; 0.01). The number of new egg masses was positively correlated with the mean precipitation and vegetation cover, and negatively correlated with the mean values of temperature, minimum daily temperature, and water depth (Table 5). Additionally, the number of new egg masses increased from day 1 until the end of the surveys.\u003c/p\u003e\n\u003cp\u003e(2) Hatching success: Based on the Pearson’s coefficient values, we excluded\u0026nbsp;vegetation cover\u0026nbsp;and the\u0026nbsp;mean values of\u0026nbsp;water temperature\u0026nbsp;and\u0026nbsp;solar radiation\u0026nbsp;from the explanatory variables. We constructed a GAMM with the hatching success as the response variable and survey day, water surface area and\u0026nbsp;the mean\u0026nbsp;minimum daily water temperature as explanatory variables (\u003cem\u003en\u003c/em\u003e = 93). The smooth term estimated for the mean water depth was statistically significant (edf = 6.1, Chi.sq = 17.05,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026lt; 0.05). The hatching success was positively correlated with the mean minimum daily water temperature and negatively correlated with water surface area (Table 6). The hatching success increased from very shallow to approximately 3 cm deep, decreased at approximately 4 cm deep, increased at approximately 6 cm deep, and subsequently decreased at greater depths (Fig. 3).\u003c/p\u003e\n\u003cp\u003e(3) Number of days until hatching: Based on the Pearson’s coefficient values, we excluded\u0026nbsp;vegetation cover and the mean\u0026nbsp;solar radiation from the explanatory variables. We constructed a GAMM with the number of days to hatch as the response variable and\u0026nbsp;survey day,\u0026nbsp;water surface area and\u0026nbsp;the\u0026nbsp;mean values of\u0026nbsp;water temperature\u0026nbsp;and\u0026nbsp;minimum daily water temperature as the explanatory variables (\u003cem\u003en\u003c/em\u003e = 81). The smooth term estimated for the mean water depth was not statistically significant (edf = 1, Chi.sq = 0.032,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026gt; 0.05). The number of days was positively correlated with the mean water temperature and negatively correlated with survey day (Table 7).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study, we investigated the environmental characteristics of an irrigation pond and rice paddies with different management and histories, \u003cem\u003eR. japonica\u003c/em\u003e breeding success, and how rice paddy environments were related to the breeding success. First, the PCA results showed that, in our study area, study sites were mainly characterized by environmental factors mainly controlled by common agricultural practices, irrigation and weed control, and aquatic thermal conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Vegetation cover increased with time after rice paddy abandonment, but other than vegetation cover, there was no clear pattern of change over time, suggesting that the management of each site primarily influenced environmental factors. Second, our GAMM results showed that \u003cem\u003eR. japonica\u003c/em\u003e spawned egg masses after rainfall, and when the air and water temperatures were relatively low. A previous study also noted the relationship between precipitation and breeding activities (Kuramoto and Ishikawa \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2000\u003c/span\u003e), and in addition, our results suggested that low temperature and water temperature were key factors for egg mass spawning by \u003cem\u003eR. japonica\u003c/em\u003e. Because \u003cem\u003eR. japonica\u003c/em\u003e is adapted to cool climates, breeding activities occurred when temperatures were relatively low during the study period. Not only the preferred breeding habitat, but also the egg-rearing aquatic habitats in relation to water temperature, water depth, and vegetation cover, are linked to important agricultural practices in rice paddies, irrigation and weed control. Next, we discussed how each of them related to the reproductive success of \u003cem\u003eR. japonica\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eIrrigation: water temperature and depth\u003c/p\u003e \u003cp\u003e \u003cem\u003eRana japonica\u003c/em\u003e preferred open areas for breeding sites. These areas appeared to improve egg mass survivorship, because during winter when breeding occurs, the water temperature could decrease to the embryonic critical thermal limit (Kadowaki \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e); however, the surface water could simultaneously be warmed by the sun to a suitable temperature for embryo development. This explains why hatching success was related to the minimum water temperature; the higher the temperature, the higher the success rate was during the study period. Cool weather is preferred for breeding, and they spawn egg masses in shallow areas so that the water temperature does not become too cold for the embryos to survive and develop. However, the number of days to hatching increased when water temperature was relatively high. During the study period, water temperatures occasionally exceeded 25\u0026deg;C. Because the gelatinous material covering the egg mass can be heated by sunlight, the temperature within the egg mass in shallow water may rise considerably above that of the surrounding water (Kadowaki \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Thus, temperatures could increase to levels too high for embryonic development in \u003cem\u003eR. japonica\u003c/em\u003e (critical thermal maximum for embryonic development is 29\u0026deg;C; Kuramoto et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1971\u003c/span\u003e). To maintain a water temperature range suitable for embryonic development, a slow water flow must be maintained through the aquatic habitat. In rice paddies, the water depth is typically low; therefore, water temperature is an important factor, especially in stagnant water.\u003c/p\u003e \u003cp\u003eOur results indicated that egg mass survival was improved with a decrease in the number of days to hatch. There were fewer days to hatch for egg masses that spawned later during the study period; the egg masses found between 14 and 30 March all hatched between 30 March and 6 April (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e). When adult frogs choose breeding sites, they avoid aquatic habitats where egg masses have already been deposited, presumably because of the risk of predation or competition with larvae that previously hatched (Iwai et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In future, the influence of egg mass density on the choice of breeding habitat, and how late-deposited egg masses catch up with the early-deposited egg masses should be studied. Practically, in cultivated rice paddies, it is better for egg masses to hatch earlier, because in April the bottom of the rice paddy is turned over and flattened by heavy machinery to prepare for rice seedling transplantation. Thus, it is difficult for larvae to survive this agricultural practice unless refugia are available. Aquatic habitats in fallow rice paddies could be safer egg-rearing habitat and provide a refuge for larvae.\u003c/p\u003e \u003cp\u003eThe relationship between hatching success and the water depth was not linear. If the water was very shallow, egg masses were at risk of drying; if the water level was deep, the water temperature could be lower than the suitable range for embryonic development. Furthermore, we found racoon (\u003cem\u003eProcyon lotor\u003c/em\u003e) footprints at our study sites. A camera trap captured \u003cem\u003eP. lotor\u003c/em\u003e, spot-billed ducks (\u003cem\u003eAnas zonorhyncha\u003c/em\u003e), and mallards (\u003cem\u003eAnas platyrhynchos\u003c/em\u003e) entering our study sites and foraging or paddling around them (Hiratsuka unpubl.). \u003cem\u003eP. lotor\u003c/em\u003e is an invasive alien species in Japan, and their negative effects on anuran species have been reported in satoyama landscapes (Kuriyama et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e); P. \u003cem\u003elotor\u003c/em\u003e was introduced in our study area in 2005, and since then the population has increased (Higashide et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The decrease in the hatching success rate at a depth of approximately 4 cm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) could be explained by the effects of \u003cem\u003eP. lotor\u003c/em\u003e; however, more studies on \u003cem\u003eP. lotor\u003c/em\u003e\u0026rsquo;s foraging habits and distribution are required to evaluate their impact on egg masses. Osawa and Hayama (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) reported that \u003cem\u003eA. zonorhyncha\u003c/em\u003e consumed \u003cem\u003eR. japonica\u003c/em\u003e egg masses. Based on the video captured by the camera trap, it was unclear whether the ducks predated the frog egg masses (Hiratsuka unpubl.), but they may have unintentionally kicked and scattered the egg masses while foraging in relatively deep water at our study sites. The hatching success rate decreased with increasing depth and was negatively correlated with water surface area. Duck foraging is more often observed in larger aquatic habitats; therefore, relatively small and shallow aquatic habitats could protect frog egg masses from ducks. By controlling the timing and amount of water flowing into the rice paddies, it is possible to create suitable breeding and egg-rearing habitat conditions for \u003cem\u003eR. japonica\u003c/em\u003e.\u003c/p\u003e \u003cp\u003eWeed control: vegetation cover\u003c/p\u003e \u003cp\u003eDuring the breeding season, male frogs wait for female frogs in the water; therefore, vegetation could be an obstacle for males, thus, they appear to avoid aquatic areas with large amounts of vegetation (Kadowaki \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Additionally, our results showed that they also avoided areas with very low vegetation coverage. The vegetation at the study sites were mainly withered plant stems from the previous year. This vegetation could function as a hiding place for male frogs while they wait for female frogs, and they may also prevent egg masses from floating away. Weed plants spread in abandoned rice paddies (Kusumoto et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2005\u003c/span\u003e); therefore, to create a sustainable suitable breeding habitat for \u003cem\u003eR. japonica\u003c/em\u003e, the water surface does not necessarily need to be cleared of weeds, but it is important to implement proper management practices to prevent weed overgrowth.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe found new egg masses in the IP, FTs, and RPs, but not in FFs, where vegetation was not managed and no pools of water were found. Our investigation revealed the relationship between \u003cem\u003eR. japonica\u003c/em\u003e breeding success and various aspects of the aquatic habitat in rice paddies with various management histories. To increase the generalizability of the suitable environmental conditions of rice paddy as breeding and egg-rearing habitats for \u003cem\u003eR. japonica\u003c/em\u003e, further investigations at multiple geographic locations are needed. Nevertheless, our study revealed the key aspects of aquatic environments associated with breeding site preference and hatching success of \u003cem\u003eR. japonica\u003c/em\u003e, and how agricultural practices, irrigation and weed control, affect breeding success by alternating the aquatic environments. The agricultural practices are essential for rice cultivation, and at the same time, they can be practical measures to improve the rice paddy environments to create preferable breeding and egg-rearing habitat for \u003cem\u003eR. japonica\u003c/em\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\n\u003cp\u003e\u003cstrong\u003eFunding and Competing Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not receive support from any organization for the submitted work. The authors have no competing interests to declare that are relevant to the content of this article.\u003c/p\u003e\n\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation and data collection were performed by Yuki Kimura and Motoshi Hiratsuka, and analysis was performed by Risa S. Naito. The first draft of the manuscript was written by Risa S. Naito and all authors commented on previous versions of the manuscript. All authors read and approved of the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe thank colleagues for helping collect data in the field. We also thank Dr. Masaru Sakai for helping to set up the data loggers and interpreting the logger data. The present study complies with the current laws of Japan in the collection and the use of animals in research and complies with the American Society of Ichthyologists and Herpetologists (ASIH) \u0026ldquo;Guidelines for Live Amphibians and Reptiles in Field and Laboratory Research\u0026rdquo; (https://bit.ly/ASIH_Herps).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eFujioka M, Lane SJ (1997) The impact of changing irrigation practices in rice fields on frog populations of the Kanto Plain, Central Japan. Ecol Res 12:101-108\u003c/li\u003e\n\u003cli\u003eGoldingay RL, Newell DA (2005) Population estimation of the Green and golden bell frog\u003cem\u003e Litoria aurea\u003c/em\u003eat Port Kembla. 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Biol Conserv 219:96-104 \u003c/li\u003e\n\u003cli\u003eKuramoto M, Ishikawa H (2000) Breeding ecology of brown frogs in Yamada park, Kitakyusyu, Japan. B Herpetol Soc Jpn 1:7-18\u003c/li\u003e\n\u003cli\u003eKuramoto M, Sumida M, Saida M (1971) Embryonic temperature tolerance in brown frogs. B Herpetol Soc Jpn 4:1-4 \u003c/li\u003e\n\u003cli\u003eKuriyama T, Asazuma Y, Takagi S (2021) Range expansion and impact for native species of invasive racoons. Jpn J Environ Entomol and Zool 32:131-136\u003c/li\u003e\n\u003cli\u003eKurniawan AH, Sato S, Cheng W, Dewi PK, Kobayashi K (2021) Animal abundance and soil properties affected by long-term organic farming in rice paddies in a typical Japanese \u003cem\u003eyatsuda\u003c/em\u003e landscape. 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Special Issue 3:9-16\u003c/li\u003e\n\u003cli\u003eUchiyama R (2005) Tanbonoikimono-zukan, Yama-kei Publishers Co., Ltd., Chiyoda-ku, Tokyo\u003c/li\u003e\n\u003cli\u003eUematsu Y, Koga T, Mitsuhashi H, Ushimaru A (2010) Abandonment and intensified use of agricultural land decrease habitat of rare herbs in semi-natural grassland. Agr Ecosyst Environ 135:304\u0026ndash;309\u003c/li\u003e\n\u003cli\u003eWashitani I (2001) Traditional Sustainable Ecosystem \u0026lsquo;SATOYAMA\u0026rsquo; and Biodiversity Crisis in Japan: Conservation Ecological Perspective. Global Environ Res 5:119\u0026ndash;133\u003c/li\u003e\n\u003cli\u003eYamazaki F (1996) A story of rice paddy. Rural Culture Association, Saitama\u003c/li\u003e\n\u003cli\u003eZheng X, Natuhara Y, Zhong S (2021) Influence of midsummer drainage and agricultural modernization on the survival of \u003cem\u003eZhangixalus arboreus\u003c/em\u003e tadpoles in Japanese paddy fields. Environ Sci Pollut Res 28:18294-18299\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Number of new egg masses of \u003cem\u003eRana japonica\u003c/em\u003e found at each study site during each survey between 14 and 30 March 2023.\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"624\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003ePI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"4\"\u003e\n \u003cp\u003eUP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"3\"\u003e\n \u003cp\u003eFF\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"3\"\u003e\n \u003cp\u003eFT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"3\"\u003e\n \u003cp\u003eRP\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003eDate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003ePI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUP1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUP2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUP3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eUP4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFF1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFF2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFF3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFT1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFT2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eFT3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRP1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRP2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003eRP3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e14-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e16-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e19-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e20-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e23-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e27-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003e30-Mar\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd\u003e\n \u003cp\u003esum\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e16\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIP, irrigation pond; UP, upstream rice paddies; FF, rice paddies fallow for five years; FT, rice paddies fallow for two years; RP, actively cultivated rice paddies. No egg masses were found before 14 March 2023 and after 30 March 2023.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003eSummary data of \u003cem\u003eRana japonica\u003c/em\u003e egg masses surveyed in each site category\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"936\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003eTotal No. of egg masses\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003eMean depth new egg masses\u003csup\u003eb\u003c/sup\u003e (cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003eDates new egg masses were found\u003csup\u003ec\u003c/sup\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eHatching success rate (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003eMean depth between the first day and the day egg masses hatched or died\u003csup\u003ed\u003c/sup\u003e (cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003eDate range when completely hatched or died\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003eNo. of days to hatch\u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003e12.8 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e14\u0026ndash;30 March\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eURs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003e3.7 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e14\u0026ndash;27 March\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e3.4 \u0026plusmn; 0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e30 March\u003c/p\u003e\n \u003cp\u003e\u0026ndash;6 April\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e14.9 \u0026plusmn; 0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eFFs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003en/a\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eFTs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003e3.7 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e19\u0026ndash;30 March\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e3.8 \u0026plusmn; 0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e30 March\u003c/p\u003e\n \u003cp\u003e\u0026ndash;3 April\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e11.6 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003eRPs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11px;\"\u003e\n \u003cp\u003e6.4 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10px;\"\u003e\n \u003cp\u003e14\u0026ndash;30 March\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12px;\"\u003e\n \u003cp\u003e85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 16px;\"\u003e\n \u003cp\u003e5.3 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14px;\"\u003e\n \u003cp\u003e30 March\u003c/p\u003e\n \u003cp\u003e\u0026ndash;6 April\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13px;\"\u003e\n \u003cp\u003e11.6 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIP, irrigation pond; UPs, upstream rice paddies; FFs, rice paddies fallow for five years; FTs, rice paddies fallow for two years; RPs, cultivated rice paddies; n/a, not applicable.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ea\u0026nbsp;\u003c/sup\u003eThe total number of egg masses found\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003e Mean \u0026plusmn; standard error (SE) of the water depth where each new egg mass was found\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ec\u003c/sup\u003e The time period during which new egg masses were found\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ed\u003c/sup\u003e Mean depth of each egg mass between the first day and the day an egg mass was found\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ee\u003c/sup\u003e The day egg masses were confirmed to have hatched or died\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ef\u003c/sup\u003e Mean \u0026plusmn; SE of the number of days it took for each egg mass to hatch.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3.\u003c/strong\u003e Summary of environmental factors for each category\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"793\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eCategory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003eMean temperature (\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eMean water temperature (\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eMean minimum daily water temperature (\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003eMean solar radiation\u003csup\u003ea\u003c/sup\u003e (kW/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eVegetation cover (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eWater surface area (m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eIP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 109px;\"\u003e\n \u003cp\u003e11.5 \u0026plusmn; 0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e10.2 \u0026plusmn; 0.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003e9.7 \u0026plusmn; 0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003e6244 \u0026plusmn; 28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e224.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eURs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"6\" style=\"width: 109px;\"\u003e\n \u003cp\u003e11.6 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003e13.3 \u0026plusmn; 0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003e7.9 \u0026plusmn; 0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003e5954 \u0026plusmn; 53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e55.9 \u0026plusmn; 9.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e14.8 \u0026plusmn; 7.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eFFs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eFF1: 10.6 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eFF1: 8.8 \u0026plusmn; 0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 112px;\"\u003e\n \u003cp\u003e6110 \u0026plusmn; 47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e100 \u0026plusmn; 0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 76px;\"\u003e\n \u003cp\u003eFTs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eFT2: 13.4 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eFT2: 8.9 \u0026plusmn; 0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 112px;\"\u003e\n \u003cp\u003e6394 \u0026plusmn; 49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 104px;\"\u003e\n \u003cp\u003e6.7 \u0026plusmn; 1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 104px;\"\u003e\n \u003cp\u003e95.7 \u0026plusmn; 88.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eFT3: 14.8 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eFT3: 11.3 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 76px;\"\u003e\n \u003cp\u003eRPs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eRP1: 10.3 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eRP1: 8.7 \u0026plusmn; 0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 112px;\"\u003e\n \u003cp\u003e1572 \u0026plusmn; 241\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 104px;\"\u003e\n \u003cp\u003e5.0 \u0026plusmn; 0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 104px;\"\u003e\n \u003cp\u003e227.4 \u0026plusmn; 16.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 135px;\"\u003e\n \u003cp\u003eRP3: 13.8 \u0026plusmn; 0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 155px;\"\u003e\n \u003cp\u003eRP3: 10.9 \u0026plusmn; 0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eIP, irrigation pond; UPs, upstream rice paddies; FFs, rice paddies fallow for five years; FTs, rice paddies fallow for two years; RPs, actively cultivated rice paddies.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003e Solar radiation between the day before the first new egg mass was found (11 March 2023) and the day all egg masses had completely hatched (6 April 2023).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4.\u003c/strong\u003e The results of principal component analysis (PCA).\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"433\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd colspan=\"4\" style=\"width: 251px;\"\u003e\n \u003cp\u003ePrincipal component\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eWTEMP\u0026nbsp;(\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.28\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.62\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.16\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.19\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eL_WTEMP\u0026nbsp;(\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.49\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.20\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.02\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.71\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eH_WTEMP\u0026nbsp;(\u0026deg;C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.36\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.56\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.04\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.27\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eSUN\u0026nbsp;(kWh/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.21\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.23\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.92\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.18\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eVEG\u0026nbsp;(%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.47\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.45\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.17\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.10\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eDEP\u0026nbsp;(cm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.53\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.03\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e-0.31\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.58\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\u003cbr\u003e\u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eStandard deviation\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e1.58\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e1.41\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.95\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.79\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eProportion of Variance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.42\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.33\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.15\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.10\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 183px;\"\u003e\n \u003cp\u003eCumulative Proportion\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.42\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.75\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e0.90\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 63px;\"\u003e\n \u003cp\u003e1.00\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe variables used for the analysis were the environmental factors measured during the study period\u0026nbsp;at each study site group (irrigation pond,\u0026nbsp;upper rice paddies,\u0026nbsp;rice paddies fallow for two years, rice paddies fallow for five years, and actively cultivated rice paddies).\u003c/p\u003e\n\u003cp\u003eH_WTEMP, mean maximum daily water temperature; WTEMP, mean water temperature; L_WTEMP, mean minimum daily water temperature; SUN, mean solar radiation mean water DEP, depth; VEG, proportion of water surface covered by vegetation\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5.\u003c/strong\u003e Summary of generalized additive mixed model analysis for breeding site preference. We constructed a model for the number of new \u003cem\u003eRana japonica\u003c/em\u003e egg masses found at each study site (\u003cem\u003en\u0026nbsp;\u003c/em\u003e= 134).\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"473\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eExplanatory variable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003eEstimate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003ez value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003e(Intercept)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e7.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e2.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eRAIN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e2.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e\u0026minus;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u0026minus;3.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eWTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e\u0026minus;0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u0026minus;0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eL_WTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e\u0026minus;0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u0026minus;3.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eSUN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e0.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eDEP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e\u0026minus;0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e\u0026minus;1.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 159px;\"\u003e\n \u003cp\u003eVEG\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 87px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 123px;\"\u003e\n \u003cp\u003e3.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe explanatory variables of the model were the mean of the following environmental factors between the previous study day and the day before the study day: RAIN, precipitation; TEMP, temperature; WTEMP, water temperature; L_WTEMP, minimum daily water temperature; SUN, solar radiation; DEP, water depth where new egg masses were found; VEG, proportion of water surface covered by vegetation. Survey day was included in the models as a smooth term (edf = 1.1, Chi.sq = 7.59,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026lt; 0.01). The log of water surface area was included as an offset term, and the categorical variable of site type was included as a random intercept.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 6.\u0026nbsp;\u003c/strong\u003eSummary of generalized additive mixed model analysis for hatching success. We constructed a model for the success or failure of each \u003cem\u003eRana japonica\u003c/em\u003e egg mass to completely hatch (\u003cem\u003en\u003c/em\u003e = 93).\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"382\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eExplanatory variable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003eEstimate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003ez value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003e(Intercept)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u0026minus;61.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e\u0026minus;2.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e\u0026lt;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eL_WTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e7.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e2.86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eDAY\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u0026minus;0.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e\u0026minus;1.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 174px;\"\u003e\n \u003cp\u003eAREA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 75px;\"\u003e\n \u003cp\u003e\u0026minus;0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 61px;\"\u003e\n \u003cp\u003e\u0026minus;2.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 71px;\"\u003e\n \u003cp\u003e\u0026lt;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe explanatory variables of the model were the mean of the following environmental factors between the first day an egg mass was found and the day it was confirmed to have hatched or died: L_WTEMP, minimum daily water temperature; DAY, survey day; AREA, water surface area. Mean water depth was included in the models as a smooth term (edf = 6.1, Chi.sq = 17.05,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026lt; 0.05), and the categorical variable of site type was included as a random intercept.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 7.\u003c/strong\u003e Summary of generalized additive mixed model analysis for number of days to hatch. We constructed a model for the number of days it took each \u003cem\u003eRana japonica\u003c/em\u003e egg mass to hatch (\u003cem\u003en\u003c/em\u003e = 81).\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"302\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003eExplanatory variable\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003eEstimate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003ez value\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003eP-value\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003e(Intercept)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u0026minus;2.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e\u0026minus;2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003eWTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e0.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e6.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003eL_WTEMP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u0026minus;0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e\u0026minus;1.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003eDAY\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e\u0026minus;0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e\u0026minus;5.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e\u0026lt;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 160px;\"\u003e\n \u003cp\u003eAREA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 73px;\"\u003e\n \u003cp\u003e\u0026minus;0.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66px;\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe explanatory variables of the model were the mean of the following environmental factors between the first day an egg mass was found and the day complete hatching was confirmed: WTEMP, water temperature; L_WTEMP, minimum daily water temperature; DAY, survey day; AREA, water surface area. Mean water depth was included in the models as a smooth term (edf = 1, Chi.sq = 0.032,\u003cem\u003e\u0026nbsp;P\u003c/em\u003e \u0026gt; 0.05) and categorical variable of site type was included as a random intercept.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"wetlands-ecology-and-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wetl","sideBox":"Learn more about [Wetlands Ecology and Management](https://www.springer.com/journal/11273)","snPcode":"11273","submissionUrl":"https://submission.nature.com/new-submission/11273/3","title":"Wetlands Ecology and Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"agroecosystem, amphibian, restoration, conservation","lastPublishedDoi":"10.21203/rs.3.rs-9126504/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9126504/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRice paddies have played an important role as a substitute habitat for wetland species. However, environmental changes and the abandonment of rice paddies have led to a decline in the number of wetland species. Moreover, rice paddies are vital habitats for sustaining the population of pond-breeding frog species. However, it remains unclear how agricultural practice influences the sustainability of frog species. In this study, we conducted surveys in 13 restored rice paddies with different management histories and one irrigation pond in the Mikajima Wetland to investigate the characteristics of the rice paddies and the relationship between the characteristics and breeding success of the Japanese brown frog (\u003cem\u003eRana japonica\u003c/em\u003e). We found 134 egg masses at 14 sites, and monitored them until they hatched, died, or were lost; environmental factors, such as water temperature and depth, were recorded. First, we conducted a principal component analysis to determine the study site characteristics. Second, we constructed generalized additive mixed models to investigate the relationship between environmental factors and the number of new egg masses, hatching success, and number of days until hatching. Our results showed that the study sites were characterized by environmental factors associated with common management practices, irrigation and weed control. The breeding success of \u003cem\u003eR. japonica\u003c/em\u003e was related to various aspects of aquatic habitats alternating between agricultural practices, and therefore, the agricultural practices can be practical measures for improving the environmental conditions in rice paddies to create preferable breeding and egg-rearing habitat for \u003cem\u003eR. japonica\u003c/em\u003e.\u003c/p\u003e","manuscriptTitle":"Agricultural practices improve breeding success of indigenous frogs in restored rice paddies: A case study from the Miyajima Wetland, Japan","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-19 16:09:09","doi":"10.21203/rs.3.rs-9126504/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-15T21:37:41+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-15T09:28:11+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-08T15:44:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"320596949537728361245432763722930965574","date":"2026-03-20T00:10:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"283074693646911567501582977609662387760","date":"2026-03-19T07:13:39+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-16T14:25:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-16T14:14:48+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-16T08:34:52+00:00","index":"","fulltext":""},{"type":"submitted","content":"Wetlands Ecology and Management","date":"2026-03-15T05:52:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"wetlands-ecology-and-management","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wetl","sideBox":"Learn more about [Wetlands Ecology and Management](https://www.springer.com/journal/11273)","snPcode":"11273","submissionUrl":"https://submission.nature.com/new-submission/11273/3","title":"Wetlands Ecology and Management","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ee3431f6-cdea-4256-a089-3efe6bdde88d","owner":[],"postedDate":"March 19th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-04-15T21:53:05+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-19 16:09:09","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9126504","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9126504","identity":"rs-9126504","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}