Data from: Climate stability drives multidimensional nestedness of amphibian assemblages in a Chinese sky island system

The nested subset pattern (nestedness) has been widely used to explain
species distributions in island and fragmented systems. Mountain sky
islands serve as critical natural laboratories for understanding the
evolutionary consequences of geographic isolation and climate change, but
their species distribution patterns remain poorly understood. Compared to
lowland fragmented habitat islands, biodiversity patterns in mountainous
regions are more complex, and traditional drivers may not adequately
explain the nestedness of sky islands. To uncover the underlying
mechanisms of mountain biodiversity, this study sampled amphibians across
30 sky islands in the Dabie Mountains, China, aiming to explore the
nestedness of amphibian assemblages and their formative mechanisms from
taxonomic, functional, and phylogenetic perspectives. Taxonomic nestedness
was quantified by constructing species incidence matrices and calculating
nestedness metrics, while functional and phylogenetic nestedness were
assessed by integrating species similarities in ecological traits and
phylogenetic relationships. Seven sky island characteristics and eight
amphibian species traits were then selected as predictors of nestedness.
Results showed that amphibian assemblages in the Dabie Mountains exhibited
significant nestedness across taxonomic, functional, and phylogenetic
dimensions. Spearman rank correlations between the selected predictors and
nestedness ranks revealed that sky island area, climate stability, and
species traits associated with extinction vulnerability were strongly
correlated with taxonomic nestedness. Additionally, sky island area and
climate stability significantly influenced functional and phylogenetic
nestedness. These findings support the "selective extinction"
and "habitat nestedness" hypotheses. To explain these results,
we propose a climate stability hypothesis specific to sky islands: stable
climatic conditions sustain greater species diversity, whereas climatic
instability exacerbates the extinction of lineages lacking adaptive
traits. This study presents the first empirical evidence of nestedness in
sky island systems, extending classical hypotheses beyond lowland
ecosystems, and offering new insights into climate-driven assembly
mechanisms affecting vulnerable taxa. Our results indicate that
conservation efforts should prioritize sky island regions with high
climate stability, large areas and diverse habitats as core areas for
biodiversity protection. Moreover, species with narrow elevation ranges,
large area requirements, high habitat specificity, and long larval stage
durations should also be preserved to prevent local extinction.