Mountain systems harbor an evolutionarily unique and exceptionally rich biodiversity, especially for amphibians. However, the associated elevational gradients and underlying mechanisms of amphibian diversity in most mountain systems remain poorly understood. Here, we explored amphibian phylogenetic and functional diversity along a 2 600 m elevational gradient on Mount Emei on the eastern margin of the Qinghai-Tibetan Plateau in southwestern China. We also assessed the relative importance of spatial (area) and environmental factors (temperature, precipitation, solar radiation, normalized difference vegetation index, and potential evapotranspiration) in shaping amphibian distribution and community structure. Results showed that the phylogenetic and functional diversities were unimodal with elevation, while the standardized effect size of phylogenetic and functional diversity increased linearly with elevation. Phylogenetic net relatedness, nearest taxon index, and functional net relatedness index all showed a positive to negative trend with elevation, indicating a shift from clustering to overdispersion and suggesting a potential change in key processes from environmental filtering to competitive exclusion. Overall, our results illustrate the importance of deterministic processes in structuring amphibian communities in subtropical mountains, with the dominant role potentially switching with elevation. This study provides insights into the underlying assembly mechanisms of mountain amphibians, integrating multidimensional diversity.

The role of ecological niche in lineage diversification has been the subject of long-standing interest of ecologists and evolutionary biologists.Gynandropaafrogs diversified into three independent clades endemic to the southeastern Qinghai-Tibetan Plateau. Here, we address the question whether these clades kept the same niche after separation, and what it tells us about possible diversification processes. We applied predictions in geographical (G)-space and tests of niche conservatism in environmental (E)-space. Niche models in G-space indicate separate regions with high suitability for the different clades, with some potential areas of sympatry. While the pair of central and eastern clades displayed the largest niche overlap for most variables, and strict niche equivalency was rejected for all clade-pairs, we found no strong evidence for niche divergence, but rather the signature of niche conservatism compared to null models in E-space. These results suggest a common ancestral ecological niche, and as such give good support to divergence through allopatric speciation, but alternative explanations are also possible. Our findings illustrate how testing for niche conservatism in lineage diversification can provide insights into underlying speciation processes, and how this information may guide further research and conservation practices, as illustrated here for amphibians on the Qinghai-Tibetan Plateau.

The observed patterns and underlying mechanisms of elevational beta-diversity have been explored intensively, but multi-dimensional comparative studies remain scarce. Herein, across distinct beta-diversity components, dimensions and species groups, we designed a multi-faceted comparative framework aiming to reveal the general rules in the observed patterns and underlying causes of elevational beta-diversity. We have found that: first, the turnover process dominated altitudinal patterns of species beta-diversity ( β _sim > β _sne ), whereas the nestedness process appeared relatively more important for elevational trait dissimilarity ( β _funcsim < β _funcsne ); second, the taxonomic turnover was relative higher than its phylogenetic and functional analogues ( β _sim > β _phylosim / β _funcsim ), conversely, nestedness-resultant trait dissimilarity tended to be higher than the taxonomic and phylogenetic measures ( β _funcsne > β _sne / β _phylosne ); and third, as elevational distance increased, the contradicting dynamics of environmental filtering and limiting similarity have jointly led the elevational patterns of beta-diversity, especially at taxonomic dimension. Based on these findings, we infer that the species turnover among phylogenetic relatives sharing similar functional attributes appears to be the main cause of shaping the altitudinal patterns of multi-dimensional beta-diversity. Owing to the methodological limitation in the randomization approach, currently, it remains extremely challenging to distinguish the influence of the neutral process from the offset between opposing niche-based processes. Despite the complexities and uncertainties during species assembling, with a multi-dimensional comparative perspective, this work offers us several important commonalities of elevational beta-diversity dynamics.

Species in transformed habitats, frequently labeled as environmental generalists, tend to show broader niches than species in natural habitats. However, how population niche expansion translates into changes in the niches of individual organisms remains unclear, particularly in the context of habitat transformation. Niche expansion could be a product of individuals having broader niches, greater distances among individuals’ niches, or a combination of both processes. This would challenge the traditional conceptions on niche dynamics, which emphasize the role played by individual specialization (IS). Here, using stable isotopes, we computed total niche width (TNW), its within- and between-individual components (WIC and BIC), and IS (the ratio WIC/TNW), in 13 populations of 6 bird species and 8 populations of 3 frog species in natural and transformed habitats. We confirmed that species had broader niche width in transformed than in natural habitats, yet population niche expansion across habitats was mainly a product of increased distance between individuals. Within each habitat type, increases in TNW were linked to increases in WIC for all habitat types, while relationships between TNW and BIC were found in transformed but not in natural habitats. Hence, both increased individual niche width and increased distance among individuals were apparent within habitats, particularly in transformed ones, where increases in WIC dominated. Neither across or within habitats was niche expansion associated with increasing IS. Therefore, our results overturn traditional conceptions associated with the niche variation hypothesis and illustrate that niche expansion is not invariably associated with increased IS, because the distance between individual’s niches (BIC) can increase, as well as the breadth of those niches (WIC).

Aim: Mountain systems offer excellent opportunities to understand β‐diversity patterns and the processes driving them. However, β‐diversity patterns and the underlying mechanisms that lead to dissimilarity in mountain amphibian communities across elevational gradients remain elusive. We aimed to evaluate how amphibian communities respond to environmental gradients with elevation and to explore how different ecological mechanisms drive elevational β‐diversity.Location: A 2600‐m elevational gradient along Mount Emei in southwestern China.Methods: We investigated elevational patterns and assembly processes of pairwise β‐diversity across three dimensions (taxonomic, phylogenetic, and functional) in turnover (i.e., species replacement) and nestedness‐resultant (i.e., species lose/gain) for amphibians. We compared multifaceted β‐diversity components and assessed the extent to which β‐diversity responded to environmental and elevational distances. We also quantified the standardized effect size of β‐diversity and its components using null models to examine the dynamics of niche‐based and neutral processes.Results: The turnover component dominated taxonomic β‐diversity, whereas nestedness was relatively more important for phylogenetic and functional dissimilarity. Moreover, taxonomic total dissimilarity and turnover were higher than their phylogenetic and functional analogues. Our results indicated a significant distance‐decay effect for multifaceted β‐diversity of amphibians on Mount Emei and found that effects and directions of predictors on multifaceted β‐diversity were different, with temperature seasonality, annual precipitation, and elevational distance acting as the most important factors. Comparing observed patterns with null‐model expectations, environmental filtering, and competitive exclusion may jointly drive elevational patterns of β‐diversity.Main conclusions: Our study emphasizes the importance of partitioning taxonomic, phylogenetic, and functional components of β‐diversity and community assembly when determining β‐diversity drivers. Although it is difficult to distinguish random communities from outcomes of niche‐based processes, this work highlights the potential roles of environmental filtering and competitive exclusion in controlling elevational communities and provides insights into amphibian community assembly in a biodiversity hotspot.