Amphibian species richness and distribution in relation to pond water chemistry in south-western Ontario, Canada

1. We assessed the patterns of amphibian species richness and distribution in relation to water chemistry over a large geographical area in 1992–94.
2. Thirteen amphibian species were observed at 180 ponds, with mean species richness 3.5 ± 0.13 species per pond (range zero to nine). Water samples were collected from 143 ponds, analysed for fifteen chemical variables, and further analysed by multivariate statistical techniques.
3. Water in the study area was hard, alkaline and well-buffered against pH change, and most ponds were eutrophic. Amphibian species richness was negatively correlated with five chemical variables (chloride, conductivity, magnesium, total hardness, turbidity).
4. Principle components analysis reduced the data set to four chemical components that explained 65.4% of the variance in the original variables. Principle component scores were retained for use in further multivariate tests. Multiple regression accounted for only 19.0% of the variance in amphibian species richness. Discriminant function analysis (DFA) was used to determine if water chemistry variables discriminated among species, but it was only able to classify 17.5% of cases correctly. DFA was also used to determine if water chemistry distinguished between used and unused sites for individual species. DFA was moderately successful, classifying 61–77% of cases correctly.
5. General water chemistry appears to play only a minor part in affecting amphibian species richness in south-western, Ontario. However, chemical variables may be helpful to distinguish between used and unused sites for some species.     

Amphibian species richness and distribution in relation to pond water chemistry in south-western Ontario, Canada

1. We assessed the patterns of amphibian species richness and distribution in relation to water chemistry over a large geographical area in 1992–94.
2. Thirteen amphibian species were observed at 180 ponds, with mean species richness 3.5 ± 0.13 species per pond (range zero to nine). Water samples were collected from 143 ponds, analysed for fifteen chemical variables, and further analysed by multivariate statistical techniques.
3. Water in the study area was hard, alkaline and well-buffered against pH change, and most ponds were eutrophic. Amphibian species richness was negatively correlated with five chemical variables (chloride, conductivity, magnesium, total hardness, turbidity).
4. Principle components analysis reduced the data set to four chemical components that explained 65.4% of the variance in the original variables. Principle component scores were retained for use in further multivariate tests. Multiple regression accounted for only 19.0% of the variance in amphibian species richness. Discriminant function analysis (DFA) was used to determine if water chemistry variables discriminated among species, but it was only able to classify 17.5% of cases correctly. DFA was also used to determine if water chemistry distinguished between used and unused sites for individual species. DFA was moderately successful, classifying 61–77% of cases correctly.
5. General water chemistry appears to play only a minor part in affecting amphibian species richness in south-western, Ontario. However, chemical variables may be helpful to distinguish between used and unused sites for some species.     

The response of amphibian communities to fish and habitat features in Mediterranean permanent ponds

Generalized linear models were used to test the effect of fish, using ponds with and without fish and habitat features as covariates, on richness and abundance of amphibian species. Five fish species and six amphibian species were recorded in 60 permanent ponds located in central Italy. The choice of covariates (macrophyte cover and pond surface area) was made after studying the correlations. The richness of amphibian species was not significantly affected by fish presence or macrophyte cover, in line with previous studies, since almost all the fish species were non-predatory. However, abundance of urodeles (newts) was negatively affected by fish and positively affected by macrophyte cover. Although fish may strongly influence the abundance and composition of amphibian communities, the results indicate that the cover of aquatic macrophytes may increase the available habitat for amphibians and therefore their abundance. Anuran species preferred ponds where fish were present, since both groups preferred larger ponds. Concordance between fish and amphibian species composition was not found by the Mantel and Partial Mantel tests. This indicates that the fish assemblages do not predict which amphibian species occur in the pond.     

Direct and indirect effects of predation on tadpole community structure in the Amazon rainforest

Abstract The relationship between the distribution of predators (fish, odonates and water beetles) and prey assemblages (amphibian larvae) was investigated in the tropical rainforest of central Amazonas, Brasil. The anuran community uses a variety of waterbodies for reproduction, ranging from streams and streamside ponds to isolated forest ponds. Predators in this system include fish in streams and streamside ponds, and invertebrates (primarily odonate naiads and beetles) in forest ponds. Tadpole species richness and assemblage structure were related to fish density and species richness. No relationships between tadpole assemblages and abiotic pond characteristics were detected. The presence offish explained much of the variation in both species composition and species richness within and among ponds. Some species of tadpole were consistently found to coexist with high densities of fish. Path analyses suggest that while fish have a strong direct effect on tadpole associations and species richness, they also have an indirect effect through invertebrate predators (odonate larvae and coleopteran beetles). Prey survival-strategies such as palatability and behaviour may explain how tadpole species composition is affected by predators at the community level. These findings suggest that the observed patterns of habitat use by larval anurans may be structured in response to the distribution of key predators (fish) in this system.     

Amphibian species richness across environmental gradients

Large‐scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long‐term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9–16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open‐canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed‐canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.     

Hurricane storm surge and amphibian communities in coastal wetlands of northwestern Florida

Isolated wetlands in the Southeastern United States are dynamic habitats subject to fluctuating environmental conditions. Wetlands located near marine environments are subject to alterations in water chemistry due to storm surge during hurricanes. The objective of our study was to evaluate the effect of storm surge overwash on wetland amphibian communities. Thirty-two wetlands in northwestern Florida were sampled over a 45-month period to assess amphibian species richness and water chemistry. During this study, seven wetlands were overwashed by storm surge from Hurricane Dennis which made landfall 10 July 2005 in the Florida panhandle. This event allowed us to evaluate the effect of storm surge overwash on water chemistry and amphibian communities of the wetlands. Specific conductance across all wetlands was low pre-storm (<100 μS/cm), but increased post-storm at the overwashed wetlands ([`(x)] \bar{x}  = 7,613 μS/cm). Increased specific conductance was strongly correlated with increases in chloride concentrations. Amphibian species richness showed no correlation with specific conductance. One month post-storm we observed slightly fewer species in overwashed compared with non-overwashed wetlands, but this trend did not continue in 2006. More species were detected across all wetlands pre-storm, but there was no difference between overwashed and non-overwashed wetlands when considering all amphibian species or adult anurans and larval anurans separately. Amphibian species richness did not appear to be correlated with pH or presence of fish although the amphibian community composition differed between wetlands with and without fish. Our results suggest that amphibian communities in wetlands in the southeastern United States adjacent to marine habitats are resistant to the effects of storm surge overwash.     

The effect of fish and aquatic habitat complexity on amphibians

Fish introductions are considered one of the most widespread anthropogenic threats to aquatic ecosystems. Their negative impact on native amphibian communities has received increasing attention in recent years. We investigated the relationship between the introduced fish, emergent vegetation cover and native amphibians in man-made ponds generated by regulation and dam building along the Tarnava Mare Valley (Romania) during the last 40 years. We inventoried amphibians and fish inhabiting 85 permanent ponds and estimated habitat complexity focusing on emergent vegetation cover. Four amphibian species were found to be negatively associated with the presence of predatory fish. Species richness of ponds without fish and ponds without predatory fish did not differ significantly, whereas ponds containing only predatory fish had significantly lower amphibian richness. A significant positive relationship was found between the emergent vegetation cover and pond occupancy of six amphibian species and amphibian species richness. As a management recommendation, we suggest the restriction of fish introductions to non predatory fish and the maintenance of high emergent vegetation cover in the ponds. Handling editor: S. Declerck     

Lentic macroinvertebrate assemblage structure along gradients in spatial heterogeneity, habitat size and water chemistry

Littoral zones of small water bodies are spatially heterogeneous habitats, harbouring diverse biotic communities. Despite this apparent heterogeneity, many studies have stressed the importance of water chemistry in determining the structure of littoral macroinvertebrate assemblages. The purpose of this study was to consider the relative importance of several spatial and water chemistry variables in explaining the patterns in the structure of macroinvertebrate assemblages in 21 lentic water bodies in northeastern Finland. Water bodies were selected to represent various habitat conditions ranging from small permanent bog ponds to small forest lakes. According to canonical correspondence analysis (CCA), the most important environmental factors related to assemblage composition were water body area, moss cover, total nitrogen and water hardness. In general, species composition in small bog ponds tended to differ from that in larger lakes with forested shoreline. Total species richness was best explained by a composite variable (PCA) describing physical habitat heterogeneity, species richness being lowest in small bog lakes with simple bottom structure and low amount of aquatic plants. Species numbers in dominant functional feeding groups were related to different environmental factors. Shredder species richness was best explained by a regression model incorporating total nitrogen and the amount of organic matter, both of which were negatively related to the number of shredder species. The number of gatherer species increased with mean substratum particle size. Scraper species richness was negatively affected by the abundance of detritus and positively affected by depth, and a model including both variables explained most of the variation. Variation in the number of predatory species was best explained by a regression model including moss cover and lake area.     

Local and Landscape Factors Driving the Structure of Tropical Anuran Communities: Do Ephemeral Ponds have a Nested Pattern?

The sets of species in animal and plant communities often comprise nested subsets of the species in broader communities. Although most mechanisms causing nested patterns are known and have been demonstrated for different environments and taxa, how amphibian communities are structured in ephemeral ponds in tropical disturbed landscapes remains unknown. We investigated if pond size, duration, presence of trees (local factors), and the proportion of forest cover surrounding ponds (landscape factor) affect anuran species richness and composition, and if pond assemblages showed a nested pattern. We sampled 11 ephemeral ponds in a pasture matrix near a large Atlantic Forest remnant in Brazil and measured local and landscape variables inside two buffer zones around each pond (100 and 500 m). We marked 1514 individuals from 23 anuran species, and found that richness in ponds ranged from 3–14 species. Both local and landscape factors explained frog species richness in the sampled ponds, and seemed to affect community composition. Frog communities occurred in a non‐nested pattern, contrary to our expectations: species found in poor subsets were not found in larger, more complex ponds. Local and landscape characteristics create a variety of environments in ephemeral ponds, even in impoverished ones; these characteristics restrict pond occupancy for some species, and result in a non‐nested pattern.     

Intermediate Pond Sizes Contain the Highest Density,Richness, and Diversity of Pond-Breeding Amphibians

We present data on amphibian density, species richness, and diversity from a 7140-ha area consisting of 200 ponds in the Midwestern U.S. that represents most of the possible lentic aquatic breeding habitats common in this region. Our study includes all possible breeding sites with natural and anthropogenic disturbance processes that can be missing from studies where sampling intensity is low, sample area is small, or partial disturbance gradients are sampled. We tested whether pond area was a significant predictor of density, species richness, and diversity of amphibians and if values peaked at intermediate pond areas. We found that in all cases a quadratic model fit our data significantly better than a linear model. Because small ponds have a high probability of pond drying and large ponds have a high probability of fish colonization and accumulation of invertebrate predators, drying and predation may be two mechanisms driving the peak of density and diversity towards intermediate values of pond size. We also found that not all intermediate sized ponds produced many larvae; in fact, some had low amphibian density, richness, and diversity. Further analyses of the subset of ponds represented in the peak of the area distribution showed that fish, hydroperiod, invertebrate density, and canopy are additional factors that drive density, richness and diversity of ponds up or down, when extremely small or large ponds are eliminated. Our results indicate that fishless ponds at intermediate sizes are more diverse, produce more larvae, and have greater potential to recruit juveniles into adult populations of most species sampled. Further, hylid and chorus frogs are found predictably more often in ephemeral ponds whereas bullfrogs, green frogs, and cricket frogs are found most often in permanent ponds with fish. Our data increase understanding of what factors structure and maintain amphibian diversity across large landscapes.     

Multiple effects of land‐use changes impede the colonization of open water in fen ponds

Question: Dutch fen areas have become embedded in intensively used landscapes, resulting in biodiversity loss. Hence, plant species that colonize open water inducing the formation of species‐rich floating peat mats have disappeared. Despite many restoration efforts, they have not returned. Is natural succession towards floating mats impeded by site conditions, dispersal limitations or changed biotic interactions? Location: Six Dutch fen reserves: De Deelen, De Weerribben, De Wieden, Westbroek, Molenpolder and Terra Nova. Methods: In 62 fen ponds we determined plant species richness and expansion into open water. We related these to habitat quality (chemical composition of soil and surface water, pond morphology), dispersal potential (distance to remnant populations, likelihood of dispersal) and biotic interactions (presence of muskrats [Ondatra zibethicus L.] and the keystone species Stratiotes aloides). Results: Factor analysis showed that plants expanded further into open water and bank vegetation had higher species richness in areas with older ponds and lower muskrat densities. Locally, high turbidity hampered colonization. Whenever the water was clear, colonization was higher in shallow ponds, and in deep ponds only if Stratiotes was present. Species richness was negatively correlated to nutrient availability in soil and positively correlated to hydrological isolation (decreased sulphate concentrations). We also found that species richness was higher in sheltered banks. Conclusions: Multiple habitat characteristics (turbidity, water depth, nutrient and sulphate concentrations) and the influence of muskrats and Stratiotes all play a role in the lack of restoration success in Dutch fen ponds. Dispersal limitations seem to be overruled by habitat limitations, as colonization often fails even when sufficient propagule sources are present, or when connectivity is high.     

Freshwater diatom and macroinvertebrate diversity of coastal permanent ponds along a gradient of human impact in a Mediterranean eco-region

Mediterranean coastal areas are characterised by heavily transformed landscapes and an ever-increasing number of ponds are subjected to strong alterations. Although benthic diatoms and macroinvertebrates are widely used as indicators in freshwater ecosystems, little is still known about the diatom communities of lowland freshwater ponds in the Mediterranean region, and, furthermore, there are few macroinvertebrate-based methods to assess their ecological quality, especially in Italy. This article undertakes an analysis of benthic diatom and macroinvertebrate communities of permanent freshwater ponds, selected along a gradient of anthropogenic pressures, to identify community indicators (taxa and/or metrics) useful to evaluate the effect of human impacts. A series of 21 ponds were sampled along Tyrrhenian coast in central Italy. Five of these ponds, in a good conservations status and surrounded by woodland were selected as ‘reference sites’ for macroinvertebrates and epipelic diatoms. The remaining sixteen ponds were located in an agricultural landscape subject to different levels of human impact. The total number of macroinvertebrate taxa found in each pond was significantly higher in reference sites than in both the intermediate and heavily degraded ones, whereas the diatom species richness did not result in a good community variable to evaluate the pond ecological quality. The analysis revealed a substantial difference among the compositions of diatom communities between reference ponds and degraded ponds. The former were characterised by the presence of several species belonging to genera, such as Pinnularia sp., Eunotia sp., Stauroneis sp., Neidium sp., all of which were mostly absent from degraded ponds. Furthermore, the taxonomic richnesses of some macroinvetebrate groups (Odonata, Ephemeroptera, Trichoptera, Coleoptera), and taxa composition attributes of macroinvertebrate communities (total abundance, percentages of top three dominant taxa, percentages of Pleidae, Ancylidae, Hirudinea, Hydracarina) significantly correlated with variables linked with anthropogenic pressures. The results of the investigation suggested that diatoms tended more to reflect water chemistry through changes in community structure, whereas invertebrates responded to physical habitat changes primarily through changes in taxonomic richness. The methodologies developed for the analysis of freshwater benthic diatom and macroinvertebrate communities may have a considerable potential as a tool for assessing the ecological status of this type of water body, complying with the European Union Water Framework Directive 2000/60/EC. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: B. Oertli, R. Cereghino, A. Hull & R. Miracle Pond Conservation: From Science to Practice. 3rd Conference of the European Pond Conservation Network, Valencia, Spain, 14–16 May 2008     

Anthropogenic changes to leaf litter input affect the fitness of a larval amphibian

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Reproductive dynamics of three amphibian species in Mediterranean wetlands: the role of local precipitation and hydrological regimes

1. Although the influence of water availability and precipitation regimes on amphibians has been studied at large scales, whether and how interannual rainfall and hydrological variations affect amphibians dynamics at a local scale have rarely been addressed. In this respect, accounting for variations in species detectability in space and time has also been overlooked. 2. We assessed the effects of rainfall and hydrological variations on the breeding dynamics of three amphibian taxa: Pelodytes punctatus, Hyla meridionalis and Pelophylax spp. in 20 ponds of the Camargue region (southern France) over a 7‐year study period. 3. We used multiple season occupancy models to test the effect of winter–spring rainfall and interannual variations in hydroperiod, mean water depth and drought events on tadpole presence in spring (March–June), a proxy for breeding dynamics. 4. We used an independent survey with spatial replicates (dipnet sweeps) to disentangle the relative contributions of phenology and detectability to the absence of records in a given month. For the three taxa considered, the probability of missing a species when that species was actually present in a pond was most often negligible. Hence, we could consider that multiseason models properly tracked changes in species phenology. 5. Pelodytes punctatus was first detected in March, while the two other taxa appeared later in April. Hyla meridionalis appeared as a mid‐season species with much more synchronous pond occupancy than Pelodytes punctatus. The detection peak of Pelophylax spp. was short and unexpectedly early for this taxon. 6. Seasonal winter–spring rainfall was associated with a decrease in extinction rates and even more strongly with an increase in colonisation rates at individual ponds. 7. Colonisation rate increased following an annual drought and was best modelled as a negative quadratic effect of the variance of pond hydroperiod. Extinction probability was best modelled by a negative quadratic effect of mean water level. Hence, breeding was more stochastic (i) in unpredictable and shallow ponds because of yearly drying up and (ii) in highly predictable and deep ponds, possibly due to the presence of predators such as fish and crayfish. 8. Overall, we show that ponds with intermediate rather than extreme variations in environmental conditions currently correspond to optimal breeding sites. Our study demonstrates that amphibian monitoring coupled with fine‐scale analysis of environmental conditions is necessary to understand species dynamics in the long run and to inform conservation efforts for these species.     

Heavy metal pollution negatively correlates with anuran species richness and distribution in south‐eastern Australia

Heavy metal pollution has likely played an important role in global biodiversity decline, but there remains a paucity of information concerning the effects of metals on amphibian diversity. This study assessed anuran species richness and distribution in relation to sediment metal content and water chemistry in wetlands located along the Merri Creek corridor in Victoria, south‐eastern Australia. Anurans were present in 60% (21/35) of study sites, with a total of six species detected: the eastern common froglet (Crinia signifera), the eastern sign‐bearing froglet (Crinia parinsignifera), the southern brown tree frog (Litoria ewingii), the growling grass frog (Litoria raniformis), the eastern banjo frog (Limnodynastes dumerilii) and the spotted marsh frog (Limnodynastes tasmaniensis). Mean species richness was 1.77 ± 0.32 per site, and species richness ranged from zero to six species per site. Across sites, species richness correlated negatively with sediment concentrations of six heavy metals: copper, nickel, lead, zinc, cadmium and mercury. Species richness also correlated negatively with wetland water electrical conductivity (a proxy for salinity) and concentrations of orthophosphate. Distributions of the three most commonly observed frog species (C. signifera, L. tasmaniensis and L. ewingii) were significantly negatively associated with the total level of metal contamination at individual sites. The study is the first to provide evidence for an association between metal contamination and anuran species richness and distribution in the southern hemisphere, adding to a small but growing body of evidence that heavy metal pollution has contributed to global amphibian decline.     

Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (～1 ha) held water for 98 days, whereas Pond II (～0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated. 2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L^?1, and increased again late in the hydroperiod. 3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond. 4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed. 5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.     

Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31–49 mS cm^–1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation‐flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorophyll content indicated that EP was eutrophic and WP mesotrophic. Phytoplanktonic species richness and diversity were low in both ponds. Algal assemblages, in terms of biovolume, were mainly dominated by Dinophyceae in EP and by Cryptophyta in WP. The zooplankton community was dominated by Rotifers (Brachionus and Hexarthra), although Copepods and Ciliates were also important. Different water inputs to the ponds, partial drying in EP during the warm season with the subsequent higher increment of salinity, and the presence of dense populations of submerged macrophytes in WP, explain the differences in plankton communities found between the two ponds.     

Amphibian richness patterns in Atlantic Forest areas invaded by American bullfrogs

The relationship between invasion success and native biodiversity is central to biological invasion research. New theoretical and analytical approaches have revealed that spatial scale, land‐use factors and community assemblages are important predictors of the relationship between community diversity and invasibility and the negative effects of invasive species on community diversity. In this study we assess if the abundance of Lithobates catesbeianus, the American bullfrog, negatively affects the richness of native amphibian species in Atlantic Forest waterbodies in Brazil. Although this species has been invading Atlantic Forest areas since the 1930s, studies that estimate the invasion effects upon native species diversity are lacking. We developed a model to understand the impact of environmental, spatial and species composition gradients on the relationships between bullfrogs and native species richness. We found a weak positive relationship between bullfrog abundance and species richness in invaded areas. The path model revealed that this is an indirect relationship mediated by community composition gradients. Our results indicate that bullfrogs are more abundant in certain amphibian communities, which can be species‐rich. Local factors describing habitat heterogeneity were the main predictors of amphibian species richness and composition and bullfrog abundance. Our results reinforce the important role of habitats in determining both native species diversity and potential invasibility.     

Is livestock grazing compatible with amphibian diversity in the High Mountains of Córdoba, Argentina?

The High Mountains of Córdoba, Argentina have a long evolutionary history of grazing by large herbivores. However, about 400?years ago, European livestock were introduced and gradually replaced native herbivores. Since the 1920s, domestic herbivores have been the only large herbivores present in the area, causing severe soil erosion and a threat to the system diversity. The endemic fauna of the region includes four amphibian species. We evaluated the effect of livestock rearing on amphibian diversity and water bodies in woodlands and grasslands of the High Mountains of Córdoba. The work was conducted on stream stretches and ponds in two contrasting grazing situations: an area with livestock presence and another area where livestock was excluded 14?years ago. The following variables were recorded at each sampling site: amphibian richness and abundance, percentage of emergent, submerged and peripheral vegetation in areas surrounding the water bodies, water pH, and water dissolved O₂. No significant differences were detected in amphibian diversity between streams of both grazing situations, whereas a greater diversity (p?<?0.01) was observed in ponds in grazed grasslands. Our results suggest that livestock rearing, qualitatively measured as grazing and 14?years of livestock exclusion, in the study area would not have negative effects on amphibian diversity. This finding might be due to the long evolutionary grazing history of the area, large-scale livestock exclusion exhibiting a novel scenario. The ongoing reintroduction of native grazers may provide the benefits of grazing without the consequent soil erosion and habitat degradation associated with domestic livestock.