Yanping Wang

Species turnover, the spatial dissimilarity in species composition, is a central concept in island biogeography and community ecology. Traditional pairwise beta diversity metrics are limited to two‐site comparisons and cannot fully resolve the mechanisms driving turnover across multiple communities. Zeta (ζ) diversity overcomes this limitation by quantifying multi‐site species sharing and capturing how both rare and widespread species contribute to species turnover along a continuum. However, existing applications of zeta diversity to birds have focused mainly on continental, urban or land‐use gradients, and have not examined island systems while simultaneously comparing phenological periods and migratory groups, nor have they separated richness differences from species replacement. As a typical land‐bridge archipelago containing multiple bird groups, the Zhoushan Archipelago of China provides an ideal system for addressing these research gaps. We surveyed forest bird assemblages across 40 islands in this archipelago. We combined zeta diversity, multi‐site generalized dissimilarity modelling (MS‐GDM) and generalized additive models, using both Sørensen and Simpson normalizations to distinguish the contribution of richness differences from that of species replacement. We classified forest birds by season (breeding vs. wintering) and by migratory strategy (resident vs. migrant), yielding five ecological groups: all forest birds, breeding birds, wintering birds, residents and migrants. We then tested whether the relative importance of island characteristics varied among these five bird groups. Zeta decay followed a pure power‐law form in all five bird groups, indicating a scale‐invariant pattern of species loss across sites. Comparing MS‐GDM results based on Sørensen‐normalized and Simpson‐normalized zeta diversity revealed a fundamental duality: island area primarily drove richness differences through selective species loss on small islands, whereas distance to the nearest mainland consistently governed true species replacement across all bird groups. Overall, our results demonstrate that deterministic assembly operates through two distinct pathways, that is area‐driven environmental filtering and isolation‐driven dispersal limitation, which jointly structure multi‐site species turnover. The richness difference and replacement duality identified here can be generalizable to other land‐bridge archipelagos and fragmented landscapes where area and isolation jointly shape community assembly, and provides a mechanistic framework for interpreting multi‐site species turnover beyond simple richness gradients.

Aim: Unravelling interactions between environmental stresses and species adaptation in habitat patches is vital for elucidating community assembly and guiding conservation. Despite growing attention to rapid habitat alteration, few studies have explored how biotic and abiotic factors jointly shape species' responses to long‐term isolation. Our objective was to address this gap by identifying the key factors that determine community assembly across distinct size gradients on land‐bridge islands. Location: Zhoushan Archipelago, the largest archipelago of China. Taxa: Amphibians. Methods: We surveyed amphibian distributions on 37 islands. Using segmented regressions, we explored whether thresholds exist in the diversity–area relationships across taxonomic, functional and phylogenetic dimensions. Incorporating life‐history traits into variation partitioning analyses, we further assessed the relative contributions of species' life‐history strategies and biogeographic factors in determining species distribution patterns along the island‐size gradient. Results: Area thresholds were observed in the diversity–area relationships across three dimensions of diversity. Below these thresholds, smaller islands consistently showed neutral standardized effect sizes for functional and phylogenetic diversity, indicating a weak influence of island area on species assembly or a predominance of random processes. Additionally, small islands favoured a group of r ‐strategy species characterized by large clutch sizes and short larval stage durations. Furthermore, fast‐slow life‐history strategies had significantly greater pure explanatory power than island area on smaller islands. Beyond these thresholds, island area became substantially more influential. Main Conclusions: Our study highlights the contrasting roles of functional adaptive strategies and biogeography in shaping amphibian distributions on islands. The identified area thresholds are critical for species conservation and indicate that management should consider the ecological strategies of target species. Specifically, small reserves may support diverse ‘fast’ amphibians but require connectivity to prevent genetic isolation. Larger reserves should preserve environmental gradients and microhabitats to sustain species with specific niche needs.

Island endemic terrestrial vertebrates, shaped by long-term isolation and ecological specialization, are particularly vulnerable to extinction pressure in the Anthropocene. However, cross-taxon extinction patterns and their drivers remain poorly understood. Here, we compiled a global dataset of 31,865 terrestrial vertebrates, including more than 7500 island endemic species, to evaluate the patterns and drivers of extinction risk in island endemics, in comparison with continent endemics and dual-range species. We found that island endemics face significantly higher extinction risk than non-island endemics, with 3.1% extinct and 34% currently threatened since 1500 CE. Extinction risk among island endemics is unevenly distributed and taxonomically structured, tightly linked to invasive species, overexploitation, and climate change. Compared with continent endemics and dual-range species, their elevated risk is closely associated with small range size and habitat specialization, while biological traits, climate, and anthropogenic pressures also exert taxon-specific effects. These findings explain the unique vulnerability of island endemic vertebrates and inform conservation priorities across island ecosystems.

Aim: Nestedness possesses the capacity to unravel the ecological mechanisms underpinning biodiversity distribution and directly inform evidence‐based conservation strategies. However, previous studies have typically been confined to individual archipelagos and have predominantly focused on taxonomic nestedness alone, neglecting its cross‐assemblage generality and overlooking the role of species traits and phylogeny in driving nested patterns. Here, we systematically identify the key variables driving the occurrences of and inconsistencies between taxonomic, phylogenetic and functional nestedness in amphibians. Location: Global. Methods: We collated data on species occurrences, traits and island characteristics for 46 amphibian assemblages worldwide. We tested for significant patterns of taxonomic, phylogenetic and functional nestedness for each assemblage. We then used a machine learning method to assess the influence of 14 extrinsic (island characteristics, environment and anthropogenic influence) and intrinsic (species traits) variables on the occurrences of and inconsistencies between three facets of nestedness. Finally, we explored how the driving variables of nestedness influence the support rates of four hypotheses. Results: Taxonomic nestedness exhibited low prevalence among amphibians and was less widespread than functional and phylogenetic nestedness. The variables influencing the occurrences of and inconsistencies between these three facets of nestedness encompassed both extrinsic and intrinsic variables. Certain key variables contributing to taxonomic nestedness showed stronger tendencies to support specific hypotheses. Main Conclusion: Our synthesis presents the first global assessment of how extrinsic and intrinsic variables shape three dimensions of nestedness in insular amphibians. Conservation biogeographers can implement targeted conservation measures for each of the 46 archipelagos based on the findings of amphibian nested patterns. Moreover, our global synthesis can provide a reference for predicting amphibian nested patterns in unstudied archipelagos, thereby facilitating the rapid development of conservation plans.