Abstract
The success of amphibian conservation efforts is highly dependent on the preservation of amphibian breeding habitats. Doñana National Park contains an abundance of ponds with heterogeneous characteristics, which has historically favoured its amphibian community. However, most of the park’s ponds are groundwater dependent, and aquifer overexploitation outside the park is leading to shorter hydroperiods and even desiccation in the pond network. This problem has been exacerbated by the scarcity of rain over the last decade. In 2021-2022, we surveyed the occurrence of the park’s 11 amphibian species, with a view to comparing our findings with those from the last previous survey in 2003-2004. We mapped the species occurrence within the park for the two survey periods. While all 11 amphibian species could still be found in Doñana, their occurrence had decreased across the board. In 2003-2004, 6 species were present across more than 50% of the sampling area. In contrast, 18 years later, such was the case for only two species (Pelophylax perezi and Hyla meridionalis). Declines were greatest for Epidalea calamita, followed by Pelobates cultripes, Triturus pygmaeus, and Lissotriton boscai. The mean number of species per sampling unit (i.e., grid cell) dropped from 4.3 to 3.1. To preserve Doñana’s amphibian community, it is important to restore the park’s pond network, which implies reducing regional groundwater overexploitation.
Introduction
Habitat loss is one of the main causes behind global amphibian declines (Blaustein and Kiesecker, 2002; Cushman, 2006; Catenazzi, 2015). Myriad factors are at work: not only anthropogenic effects, such as pollution, land transformation, or the desiccation of aquatic habitats, but also global changes in temperature and precipitation, which alter hydrological cycles in amphibian breeding habitats (Corn, 2005). Most amphibians require water to reproduce, which means they need access to suitable reproductive habitats, such as temporary ponds or wetlands (Semlitsch, 2003; Gomez-Mestre et al., 2012). Thus, protecting potential breeding habitat is key in efforts to manage amphibian populations.
In particular, broad areas containing diverse wetlands can sustain high amphibian diversity because they harbour breeding sites for species with different egg-laying and developmental requirements (Beja and Alcázar, 2003; Gómez-Rodríguez et al., 2009). Most species lay eggs in the water, which hatch into aquatic larvae that metamorphose into land-living juveniles. Therefore, the length of the larval phase frequently determines species-specific habitat requirements. Common breeding sites are temporary ponds because the levels of predation pressure faced by larval amphibians are lower than in permanent waters (Wellborn et al., 1996). In these aquatic habitats, amphibians are major primary consumers (anuran larvae; see Arribas et al., 2014, 2015; Pinero-Rodríguez et al., 2021) or predators (urodele larvae and adults; see Díaz-Paniagua et al., 2005, 2015; Williams, 2006; Arribas et al., 2015). Pond drying is one of the main risks encountered by amphibians in these habitats. Species have specific requirements regarding the duration of inundation (i.e., the hydroperiod): it must be long enough to allow larval development to reach completion, or there will be high levels of larval mortality and reproductive failure.
Amphibians differ greatly in their reproductive characteristics (Semlitsch and Skelly, 2008). In pond-breeding amphibians, such differences mostly involve larval period length and phenology (Díaz-Paniagua, 1992; Semlitsch and Skelly, 2008), leading to variation in optimal breeding habitat. Thus, ephemeral ponds host species whose larval development lasts a few weeks or months, providing habitat in which competition and predation is limited. Some of the main factors influencing larval survival, size at metamorphosis, and adult fitness in ponds are hydroperiod duration, competition, predation, and resource availability (Wilbur and Collins, 1973; Smith-Gill and Berven, 1979). The availability of heterogeneous ponds differing in structural, physicochemical and biotic characteristics therefore furnishes diverse habitat that meets the breeding requirements of numerous species. Unfortunately, even though temporary ponds are essential to the reproduction of temperate amphibians, their conservation has largely been neglected, and they are disappearing worldwide (Grillas et al., 2004; Zacharias and Zamparas, 2010; Calhoun et al., 2017; Parra et al., 2021). This alarming pattern is affecting the persistence of amphibian species and other taxa.
(A): Map of Doñana National Park (SW Spain) showing the sandy area (stabilized and moving dunes), and marsh. It also includes the cartography of temporary ponds, and permanent ponds (as per Gómez-Rodríguez et al., 2011). (B): Ponds sampled and the percentage of terrestrial vegetation observed in their basins.
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
Doñana National Park has long been considered a bastion of amphibian conservation (Mateo et al., 1996) because it harbours an abundance of breeding sites. The park is home to a network of highly numerous and heterogeneous ponds as well as a large marsh, which together host 11 of the 13 amphibian species native to southwestern Spain (Díaz-Paniagua et al., 2005). In 2003-2004, a survey was conducted in the park to characterize amphibian distributions; for most species, there was a strong positive relationship of amphibian occurrence with breeding habitat availability and the persistence of the ponds’ natural hydrological regimes (Díaz-Paniagua et al., 2006). Around 20 years later, the park is facing the deterioration of its ecosystems in general and that of its groundwater-dependent aquatic habitats in particular (de Felipe et al., 2023). After the park was officially created in the 1970s, various efforts were made to promote farming and tourism in neighbouring areas, and the resulting groundwater demands have caused the phreatic level of Doñana’s aquifer to gradually decline (Custodio et al., 2009; Dimitrou et al., 2017). At present, the aquifer is considered to be overexploited, especially in the park’s northernmost zones, where researchers have observed decreases in pond hydroperiods and inundation surfaces, including an absence of flooding in around 60% of ponds (de Felipe et al., 2023). The pond network’s current state might be translating into fewer breeding habitats for amphibian species. However, potential long-term consequences of this concerning trend on amphibian abundance remain unexplored.
In this study, we assessed the effects of wetland network condition on Doñana’s amphibian community. We conducted surveys in the spring of 2021 and 2022 to update the distribution records obtained in the spring of 2003 and 2004 (Díaz-Paniagua et al., 2006). Amphibian assemblages may experience wide changes in species composition and abundance across years (Gómez-Rodríguez et al., 2010a). In this context, it is important to note that conditions were much drier during the 2021-2022 survey than during the 2003-2004 survey. Consequently, by necessity, we are comparing species distributions during a disfavourable period with those during a favourable period. This reflects current climatic realities – there have been no favourable periods over the last 10 years, and updating knowledge on the species’ distributions has become a pressing conservation concern. We hypothesize that, over the past 20 years, decreases in pond availability and hydroperiod duration have negatively affected patterns of amphibian occurrence in Doñana National Park. The greatest impacts should be detected in species that breed in ponds with either the shortest or the longest hydroperiods, given the reduction in pond flooding. However, generalist species should also be affected by diminished pond availability and connectivity, given the prevailing matrix of pond desiccation.
Materials and methods
Study area
Doñana National Park extends over 54 252 ha in southwestern Spain and is located between the Atlantic Ocean and the mouth of the Guadalquivir River. It contains over 27 000 ha of marshes that are underlain by a clay substrate; the marshes are seasonally flooded, via heavy autumn or winter rains, and usually dry up during the summer. The remainder of the park is characterized by both moving and stabilized sand dunes (fig. 1A). Under the park is a large aquifer of around 2700 km2 (Manzano et al., 2009), which spans beyond Doñana’s perimeter. In the sandy part of the park, more than 3000 ponds may be inundated in rainy years (Gómez-Rodríguez et al., 2011; fig. 1a). Most are groundwater dependent and classified as Mediterranean temporary ponds, a priority habitat for conservation (EU Habitat Directive code 3170*). They flood annually, when accumulated autumn or winter precipitation recharges the aquifer and the phreatic level rises above the lowest point of the pond basins. This marks the start of their annual inundation cycles. Most ponds dry up in the summer, with the exception of a few large ponds at the centre of the park. This area is close to the advancing front of the moving dunes, and groundwater discharge from beneath the dunes converges with discharge from the large regional aquifer. Within the park, these ponds have the greatest surface areas and longest hydroperiods. Two are classified as semipermanent because they only dry up occasionally in dry years. The largest and deepest pond is considered to be permanent, although it has dried up in summers of exceptionally dry years (Díaz-Paniagua and Aragonés, 2015), such as 1983, 1995, and 2022 (the second year of our survey). Temporary ponds are highly abundant and are the main reproductive habitats used by amphibians in Doñana (Díaz-Paniagua, 1990; Díaz-Paniagua et al., 2009; Gómez-Rodríguez et al., 2009). Their degree of inundation varies widely among years, tracking the unpredictable rainfall that characterizes the area’s Mediterranean climate. Thus, ponds may start filling in the autumn, winter, or spring, depending on the year. Although natural permanent ponds are scarce, Doñana hosts around 200 ponds that have been artificially deepened to ensure water availability year round, which are called zacallones by locals. They are small and deep (dimensions: ∼15 m × 4 m, max depth: ∼2 m). Because they were generally formed by digging up the basin of natural ponds, they are also affected by local groundwater fluctuations. For the purposes of this study, the natural, semiartificial permanent, and semipermanent ponds are considered to form part of the park’s “permanent” wetlands. During rainy periods, small shallow streams are formed that channel runoff from the sandy area to the marsh. In the spring, these streams turn into a disconnected chain of temporary ponds. The ponds formed in the mouth of these streams, located along the marsh’s edge, were usually permanent in past decades, but they have started to dry out in the summers of recent years. In the marsh, a large, continuous sheet of water is generated during the rainy season which also tends to dry out in the summer. It is mostly freshwater but grows more brackish towards the mouth of the Guadalquivir River. In very dry years, the marsh may not flood, and water may only persist in isolated deep points.
The Doñana pond network was described in detail by Gómez-Rodriguez et al. (2011), who identified 2867 ponds in the park’s sandy area in 2004. There were 2-3 large ponds considered permanent or semipermanent as well as around 15-20 intermittent streams that formed permanent ponds along the marsh’s border, and approximately 200 zacallones. The remaining ponds (∼2600 ponds) were temporary and tended to be small (more than 1150 ponds of less than 50 m2). Most ponds were located at the park’s centre, notably in the ecotone between the moving and stabilized dunes. This zone separates the northern area, with high pond density, from the southern area, with low pond density.
The local climate is Mediterranean with an Atlantic influence, characterized by mild winters and warm summers. From 1978-1979 to 2021-2022, mean annual rainfall was 530 mm during the hydrological cycle (September to August). That said, rainfall quantity and timing varied substantially among years, resulting in alternating highly wet and highly dry hydrological cycles (
Amphibian survey
In this study, we characterized the distributions of Doñana’s 11 amphibian species, which were last surveyed in the spring of 2002 and 2003 (hereafter, 2002-2003 survey period; see Díaz-Paniagua et al., 2006). The survey described herein was conducted in the spring of 2021 and 2022 (hereafter, 2021-2022 survey period), after 10 years of low rainfall.
During the 2002-2003 survey period, we documented amphibian occurrence at 327 sites. The pond network had changed in the 2021-2022 period, as 60% of the ponds had dried up (de Felipe et al., 2023). During the 2021-2022 survey period, we recorded amphibian occurrence at 132 sites. This number does not include 33 additional sites that were visited but that were dry; an additional 16 were desiccated and had been colonized by terrestrial vegetation. A total of 89 sites were characterized during both survey periods (table 1).
Description of the study’s sampling structure. Sampling site numbers are indicated by habitat type and survey period. Also shown are the additional number of ponds that could not be sampled in 2021-2022 because they did not flood during that study period (Dry) or because they had dried-up permanently (Desiccated).
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
For amphibian surveys, we performed different techniques. We conducted dipnetting in 292 ponds and counted the number of amphibians captured (most were larvae). We also collected data on the presence of eggs and adults displaying courtship behaviour, via visual inspection of the ponds, as well as data on anurans detected via calls. We supplemented our data with information provided by Doñana’s natural processes monitoring team, which is part of the park’s amphibian assessment program. The latter has been in operation since 2003 and conducts yearly amphibian surveys, using the methods described above, as well as baitless static funnel traps, which are placed in ponds for 12 h to passively capture moving individuals. We included data from 35 of the program’s sites, focusing exclusively on species presence in each pond.
We elaborated amphibian distribution maps dividing the study area in 1 km × 1 km grid cells. Each grid cell was associated with data on individual species presence and total species number. In total, we compiled data for 128 grid cells for the 2003-2004 survey period, and data for 106 grid cells for the 2021-2022 survey period (including 16 grid cells strictly associated with dry ponds). There were 79 grid cells with data for both periods, which increased to 87 when including grid cells with ponds that were dry during the second survey period.
To assess the species-specific patterns of occurrence across habitats during each survey period, we assigned each site to one of four categories based on aquatic habitat type: temporary ponds, permanent ponds, streams, and marsh. We considered the number of sites of different types of habitats in which each species was observed in relation to the total number of sampled sites of each habitat.
Pond survey
In 2021 and 2022, we continued to visit ponds that had not flooded, gathering information about their conservation status. For these ponds, we visually estimated the percentage of the basin colonized by terrestrial vegetation (e.g., scrub, heath, bushes, and pine trees). We also examined basin surface area and surrounding open ground for 267 ponds using orthophotos. We employed an image comparison tool (Instituto Geografico Nacional, https://www.ign.es/web/comparador_pnoa/index.html#) to measure basin perimeter across years. Finally, we verified these estimates for 95 ponds by visiting them in the field; we also recorded the terrestrial plant species found in their basins.
Statistical analyses
The species distributions were described using maps with 1 km × 1 km grid cells. While all grid cells with species presence data were mapped, we only conducted statistical analyses on grid cells for which repeated data were available (2003-2004 and 2021-2022 survey periods, n = 87). Because pond desiccation has major impacts on amphibian conservation, we analysed differences between both periods including grid cells with species occurrence data for the 2003-2004 survey period and grid cells with species occurrence data plus those that were dry in the 2021-2022 survey period (i.e., no species present). The maps were constructed using Qgis (v. 3.16).
Statistical analyses were performed using R (v.4.1.1; R Core Team, 2021). To compare species occurrence across the two survey periods, we used generalized linear mixed models (GLMMs) with a binomial error distribution. In each model, the response variable was species presence or absence (whether due to a true absence or a lack of detection) for each grid cell; the explanatory variable was survey period. Additionally, grid cell identity was included as a random factor. Furthermore, the number of species per grid cell was compared across study periods using a GLMM with a Poisson error distribution, using the “lme4” package (Bates et al., 2015). The significance of the terms in the models was tested with Wald’s (Type II) Chi-squared tests, performed with the “car” package (Fox and Weisberg, 2019).
Results
Deterioration of the pond network
During the 2021-2022 study period, we have witnessed a deterioration of Doñana’s pond network over recent decades, illustrated by the shrinkage or disappearance of the pond basins and the encroachment of terrestrial vegetation. These effects have largely been observed in the north-western zone of the park (fig. 1, supplementary fig. S1). Of 267 ponds that were visited in the field or analysed via orthophotos, only 10% showed no evidence of deterioration (5% in the north and 5% in the south). Terrestrial vegetation had invaded the ponds to varying degrees: 52% of the ponds had vegetation covering 1-50% of their basins; 19% of the ponds displayed coverage of 51-90%; and 19% of the ponds had been fully invaded. In the latter, the basins had disappeared under layers of helophytes (e.g., Juncus maritimus, Juncus acutus), scrub species (Halimium halimifolium, Rubus ulmifolius, Ulex minor, Erica scoparia), and bushes or trees (Tamarix gallica, Pinus pinea).
Pond hydroperiods have also changed in recent decades. Classified as permanent in the 2003-2004 survey period, the ponds formed by the mouth of the streams became temporary over the last 10 years and have dried out completely during recent summers. One of the two semipermanent ponds has dried out every summer since 2012. In the other, only 50% of the basin remained flooded through the summer of 2021; it even dried out completely in the summer of 2022, as also had occurred in 2014. Additionally, most of the permanent zacallones (42 of the 65 visited) dried out in the summers of 2021 and 2022. Furthermore, the marsh has experienced less extensive flooding area and shorter hydroperiods (Green et al., 2024). Finally, 23 of the sites sampled during the 2003-2004 survey could not be sampled again during the 2021-2022 survey because they were dry.
Updating amphibian distributions
We mapped the distributions of the 11 amphibian species found in the study area during the two survey periods (fig. 2).
Occurrence of each amphibian species in Doñana National Park during the 2003-2004 and 2021-2022 survey periods. The first map shows the grid cells sampled during each survey period; in orange are the grid cells only surveyed in 2003-2004, in dark green are those only surveyed in 2021-2022, and in light green are those sampled during both periods. Red-bordered are the grid cells with data for 2003-2004 from ponds that were dry in 2021-2022. Similar colours are shown for the species occurrence maps.
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
Number of grid cells in which each amphibian species occurred in the 2003-2004 and 2021-2022 survey periods. (Number of grid cells in 2003-2004 = 128, number of grid cells in 2021-2022 = 102).
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
During the 2003-2004 survey period, five species occurred in more than 50% of the total number of grid cells sampled (N = 128). Among them, Pelophylax perezi, Pleurodeles waltl, Hyla meridionalis, Pelobates cultripes, and Triturus pygmaeus exhibited high levels of occurrence, with P. perezi at the top (67%). During the 2021-2022 survey period, only P. perezi and H. meridionalis continued to occur at ⩾50% of the total number of grid cells sampled in that period (N = 102). All species exhibited lower levels of occurrence than during the 2003-2004 survey, with the exception of A. cisternasii, which only occurred in a stream in the extreme northwest of the park during both survey periods (figs. 2 and 3). We found no significant differences between the two survey periods regarding the occurrence of Pelodytes ibericus (
Number of amphibian species in each grid cell in the 2003-2004 and 2021-2022 survey periods (grid cells with red borders = dry ponds with 0 species).
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
The number of species per grid cell dropped significantly (
Reproductive habitats
During the first survey period, temporary ponds were extremely abundant in the sandy area, and it was the most surveyed type of habitat. In 2021 and 2022, we surveyed more permanent (mostly zacallones) than temporary ponds, due to the lower number of ponds flooded in the park. Also the marsh had a lower number of prospected sites. Despite these changes, five species did not differ in the most frequent type of habitats between the two periods (Alytes cisternasii, E. calamita, P. ibericus, P. perezi and P. waltl). Of these, in the second survey period, P. ibericus was not observed in streams and permanent sites, E. calamita did not appear in streams and marsh, and P. waltl was not found in streams. The other species shifted their most frequent habitat between both periods. For H. meridionalis, the marsh was the habitat with the highest proportion of occurrence. Triturus pygmaeus and L. boscai were mostly found in temporary ponds and were entirely absent from the streams and marsh, and B. spinosus was mostly observed in permanent ponds and was not observed in streams and marsh (table 2).
Number of sites of Doñana’s amphibian species in each habitat type – permanent ponds, temporary ponds, streams, and the marsh – during the 2003-2004 and 2021-2022 survey periods. The percentages of occurrence (%) are shown in brackets, estimated in relation to the total number of habitat types sampled. The values of the habitat type with the highest frequency for each species are shown in bold.
Citation: Amphibia-Reptilia 45, 2 (2024) ; 10.1163/15685381-bja10179
Discussion
Doñana National Park contains a wide variety of aquatic habitats well suited to amphibian reproduction, conditions that have facilitated the conservation of the park’s 11 amphibian species in general and of the pond breeders in particular (Gómez-Rodríguez et al., 2009). In this study, we observed declines in amphibian occurrence, which were linked to the deterioration of the pond network within the park’s sandy areas.
More than 70% of amphibian species are in decline worldwide because of global changes (Baillie et al., 2004; Stuart et al., 2004; Hayes et al., 2010), and 41% of the species on the IUCN red list are classified as threatened with extinction (Luedke et al., 2023). Most species in the Iberian Peninsula are currently included in red lists (Pleguezuelos et al., 2002; Cox et al., 2006). Previously, Doñana National Park was an exception: abundances were high for most of its 11 amphibian species (Díaz-Paniagua et al., 2006). The preservation of the ponds’ hydrological dynamics, including inter- and intra-annual variation, has been considered of crucial importance in the conservation of amphibians (Gómez-Rodríguez et al., 2010a, b), aquatic macroinvertebrates (Florencio et al., 2009, 2011), and zooplankton communities of the Doñana National Park (Florencio et al., 2020). The problem is that Doñana ponds are groundwater dependent, and their inundation/desiccation cycles have been altered by the gradual decline in groundwater levels that have been underway since the 1980s (Custodio et al., 2009; de Felipe et al., 2023).
Climate change has also affected pond dynamics, as the local area has experienced a long period of abnormally low rainfall (2011-2022). The region’s Mediterranean climate is characterized by pronounced interannual variability in the amount and timing of rainfall, which means that there will be a certain amount of unpredictability around the start date of temporary pond and marsh inundation. The reproductive cycles of the park’s amphibians are attuned to this variation. Temporal segregation in reproduction is highest in wet years with heavy autumnal rains. Some species breed early, starting in the autumn, while most of the other species always begin breeding in late winter; there is even a late-breeding species (Pelophylax perezi), which does not reproduce until late spring or summer (Díaz-Paniagua, 1990). Consequently, variation in the season of pond filling leads to differences in amphibian community composition among years and, in the longer term, maintains the abundance of the park’s most prominent species (Díaz-Paniagua et al., 2009; Gómez-Rodríguez et al., 2010a, b). In years when flooding does not occur in the autumn, most species end up breeding from winter to spring. This increases larval density and levels of resource competition, resulting in differences in species abundances tied to different levels of resource availability in different habitat types (Gómez-Rodríguez et al., 2010a). Because there has been no autumnal flooding in the last decade, early breeding species have been particularly impacted. For example, for P. cultripes, P. ibericus, and P. waltl, levels of occurrence declined by more than 20%.
While Doñana National Park still hosts populations of all the amphibian species observed in the first survey, levels of occurrence decreased across the board; and the mean number of species per km2 decreased 29% between survey periods. This pattern was largely driven by the increase in the number of grid cells with no amphibians, which were strongly associated with desiccated ponds in particular areas of the park, namely those most severely affected by regional groundwater abstraction for anthropogenic uses (de Felipe et al., 2023). Except for a species that was already rare in the area (A. cisternasii), all other species exhibited a considerable reduction in their distribution ranges in the park. The species most affected was E. calamita, whose occurrence was reduced by 36%. This species usually breeds in ephemeral pools, and tadpoles develop rapidly, facing no interspecific competition (Díaz-Paniagua, 1990; Gómez-Rodríguez et al., 2010a) and little predator pressure (see Portheault et al., 2007). Thus, the shorter pond hydroperiods during the 2021-2022 survey period are unlikely to be the reason for this species’ decline; instead, it may have suffered from an increase in interspecific interactions, which could have reduced larval survival. Furthermore, the lower rainfall that occurred during the second survey period led to limited flooding of the ephemeral ponds, making them less available to the species, which may have also reduced its reproductive success. It is possible that D. galganoi faced similar challenges because its larvae develop rapidly in ephemeral ponds and are greatly affected by interspecific competition (Gómez-Rodríguez et al., 2010a). However, in contrast to E. calamita, D. galganoi more frequently engages in opportunistic egg-laying, which may have buffered reductions in its reproductive success (Díaz-Paniagua, 1988, 1992).
Occurrence of the two newt species also dramatically declined from the first to the second survey period, likely as a result of decreased pond availability. In the past, the newts commonly occurred in most ponds in the northern area of the park, of which many have now disappeared. During the first survey period, rainfall levels and pond hydroperiod durations were greater, which likely explains the presence of P. ibericus and B. spinosus in other ponds in the vicinity of their optimal reproductive habitat (Díaz-Paniagua et al., 2006). However, during the second survey period, this was no longer the case, as they were only found in their typical reproductive habitats in this area: P. ibericus was restricted to the marsh, and B. spinosus only occurred in the permanent ponds. In the first survey period, the more aquatic species (P. perezi) tended to occur in zacallones throughout the park (Díaz-Paniagua et al., 2006). Of all the amphibians in the park, P. perezi is the only late-breeding species: its larval development extends into the summer in long- hydroperiod ponds or permanent waters. The recent deterioration of the pond network and low rainfall levels have contributed to many of the zacallones completely drying out in the summer; the previously permanent stream-formed ponds along the edge of the marsh have suffered the same fate. These patterns may explain the species’ reduced occurrence. Although the availability of aquatic habitats in the park has diminished, there remain sufficient zacallones scattered throughout the area to explain the persistence of P. perezi across both survey periods. Similarly, although H. meridionalis and the two newt species were negatively affected by the disappearance of ponds, they may have been able to breed successfully in temporary or permanent water bodies, which may have limited the impacts on their populations.
High pond densities favour population connectivity, which is key to the viability of amphibian populations because it allows juvenile dispersal and regional turnover of the species in amphibian communities (Cushman, 2006). Accordingly, pond density in northern Doñana has promoted amphibian genetic diversity, as observed in P. perezi and P. waltl (Sanchez-Montes et al., 2024), as well as in T. pygmaeus (Albert and García-Navas, 2022). The latter studies identified well-differentiated clusters displaying among-pond genetic admixture, which largely appears to be explained by the high degree of pond connectivity facilitating the movements of reproductive adults, even among distant points within the park. Similarly, the high connectivity of Doñana’s pond network has resulted in the park’s newt populations demonstrating far greater genetic diversity than that seen in neighbouring populations outside the park (Albert and García-Navas, 2022). Maintaining this connectivity is essential to preserve the high genetic diversity of these amphibian populations. Consequently, aquifer overexploitation and reduced rainfall pose serious conservation threats, since pond density has declined in the areas displaying the highest levels of connectivity and genetic diversity. Reduced network connectivity may not only affect amphibian abundance within certain habitats but may also reduce the genetic diversity of amphibian populations.
For the moment, Doñana still retains all of its amphibian species. However, we have documented that most of the park’s amphibians have been negatively affected by pond losses, which are the result of anthropogenic disturbances. To preserve the park’s amphibian community, it is crucial to restore the pond network’s hydrological dynamics. The first step is to reduce groundwater abstraction in the areas around Doñana.
Corresponding author; e-mail: poli@ebd.csic.es
Acknowledgements
We thank the ICTS-RBD facilities for providing field support and data. We are also grateful to the Laboratory of Remote Sensing at the Doñana Biological Station (LAST-EBD) for helping with the maps. Our study was funded by the Spanish Ministry for Science and Innovation (projects PID2019-104343RB-I00 and PID2019-104580GA-I00/AEI/10.13039/501100011033). MdF was supported by an FPI grant PRE2020-093367 from the Spanish Ministry of Science and Innovation.
Supplementary material
Supplementary material is available online at: https://doi.org/10.6084/m9.figshare.25638426
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Footnotes
Associate Editor: Guillermo Velo-Antón
