Habitat fragmentation is a major cause of biodiversity loss. Fragmentation can alter thermal conditions on the remaining patches, especially at habitat edges, but few studies have examined variations in thermal tolerance of species in fragmented habitats. Ants are sensitive to both habitat fragmentation and temperature changes, and are an ideal taxon for studying these impacts. Here, we focused on the dimorphic ant species Pheidole nodus in a fragmented habitat island system (Thousand island lake) in China. We assessed critical thermal maximum (CTmax), minimum (CTmin), and range (CTrange) temperatures for both minor (workers) and major workers (soldiers) of 2307 individuals from 117 edge and interior colonies across 9 islands during relatively hot and cold seasons. Using mixed-effect linear models, we explored the effects of island area, habitat type (edge vs. interior), season, and caste (worker vs. soldier) on CTmax, CTmin, and CTrange. We found temperatures were 1–3 ℃ higher in edge than interior sites in relatively hot season. Yet, only CTmax and CTrange in edge populations were higher than those of interior sites on smaller islands. CTmax was higher in relatively hot season and CTmin was lower in relatively cold season, indicating seasonal plasticity in thermal tolerance. Workers consistently had higher CTmax and lower CTmin than soldiers. These findings underscore the importance of seasonality, worker caste, and interactive effect between island area and habitat type in shaping thermal tolerance of a dominant dimorphic ant species on fragmented habitat islands. Our study provides a roadmap for integrating thermal biology into studies of how fragmentation impacts biodiversity.

Beta diversity, the variation of community composition among sites, bridges alpha and gamma diversity and can reveal the mechanisms of community assembly through applying distance-decay models and/or partitioning beta diversity into turnover and nestedness components from functional and phylogenetic perspectives. Mountains as the most natural experiment system provide good opportunities for exploring beta diversity patterns and the underlying ecological processes. Here, we simultaneously consider distance-decay models and multiple dimensions of beta diversity to examine spatial variations of bird communities, and to evaluate the relative importance of niche-based and neutral community assembly mechanisms along a 3600-m elevational gradient in the central Himalayas, China. Our results showed that species turnover dominates taxonomic, functional, and phylogenetic beta diversity. We observed strongest evidence of spatial distance decays in taxonomic similarities of birds, followed by its phylogenetic and functional analogues. Turnover component was highest in taxonomic beta diversity, while nestedness component was highest in functional beta diversity. Further, all correlations of assemblage similarity with climatic distance were higher than that with spatial distances. Standardized values of overall taxonomic, functional, and phylogenetic beta diversity and their turnover components increase with increasing elevational distance, while the standardized values of taxonomic and phylogenetic nestedness decreased with increasing elevational distance. Our results highlighted the niche-based deterministic processes in shaping elevational bird diversity patterns that were determined by the relative roles of decreasing trend of environmental filtering and increasing trend of limiting similarity along elevation distances.