Abstract
AbstractAimPatterns of diversity along elevational gradients are driven by species characteristics but remain poorly understood. Filling this gap is imperative given the deteriorating conservation status of anurans worldwide. Here, we examine frog diversity and species composition along a sharp subtropical elevational gradient and assess the degree to which these are determined by environmental and spatial predictors.LocationAn extensive southern Brazilian Atlantic Forest elevational gradient ranging from 300 to 1,800 m above sea level.MethodsWe sampled 38 ponds and used structural equation modelling to examine the direct and indirect effects of area, climate, habitat amount, habitat complexity and productivity on frog species richness and abundance. We also applied joint species distribution models to investigate the importance of these predictors on frog species composition using species distribution and co‐occurrence along the elevational gradient.ResultsWe recorded 12,636 individuals of 41 frog species. Frog species richness was highest at intermediate elevations, showing a hump‐shaped pattern. Frog abundance was highest at lowlands and decreased towards higher elevations. We found support for only the habitat amount hypothesis in explaining overall species richness. Although temperature had a positive influence on productivity and frog abundance, neither predictors were related to species richness. Species composition diverged markedly between lowland and highland frog assemblages, which was mainly attributed to differences in ambient temperature.Main conclusionElevations containing more extensive natural habitat areas retained the most species‐rich frog assemblages. The mid‐elevational peak is likely attributed to lowland habitat (<800 masl) heterogeneity and extreme climatic conditions in highland areas (>1,400 masl). The entire elevational gradient is, however, critical in maintaining anuran species diversity as lowland assemblages are distinct from those at mid‐ to high elevations. Our study also shows that anthropogenic habitat loss has a decisive effect on montane frog diversity, reinforcing the need to effectively protect these areas.
Highlights
Biodiversity heterogeneity along environmental gradients is a central topic in ecology and biogeography (Lomolino, 2001; Ricklefs, 2004)
Our study shows that different components of anuran species diversity are influenced by mechanisms related to environmental filtering along the elevational gradient
Frog species richness was strongly associated with the proportion of natural habitats remaining within each elevational zone, while frog abundance was highly associated with mean annual temperature
Summary
Biodiversity heterogeneity along environmental gradients is a central topic in ecology and biogeography (Lomolino, 2001; Ricklefs, 2004). Diversity scales to the available habitat area, and montane regions covering larger areas or providing more available habitat should harbour more species and individuals (Fahrig, 2013; Rosenzweig, 1995) This area–diversity relationship is based on the assumption that larger habitat areas reduce extinction rates and are more likely to encompass more habitat types (MacArthur & Wilson, 1967; Rosenzweig, 1995). Biotic processes such as competition, habitat complexity and habitat heterogeneity across ecotones have been proposed to explain elevational patterns of diversity (Beck et al, 2017; McCain & Beck, 2016; McCain et al, 2018). The contribution of these factors to montane diversity remains unclear given the difficulty in measuring these processes along natural elevational gradients
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