Abstract
Aim Understanding the mechanisms shaping biodiversity patterns, particularly the role of community assembly processes, remains a central challenge in ecology. In this study, we examine how climate and anthropogenic pressures jointly drive community assembly and biodiversity patterns through taxon co‐occurrence analyses. Location Southwest China, East Asia. Taxa Chironomids. Methods Spatial chironomid data from 129 lakes (3297‐m elevational gradient) across southwest China and a century‐scale subfossil chironomid record from an alpine lake, Tiancai, were used to assess taxon co‐occurrence and biodiversity patterns across space and time, and linked to environmental drivers including climate and human impact. Results Spatially, chironomid richness exhibited a unimodal elevational pattern, peaking at mid‐elevations (3011–4014 m a.s.l.) where co‐occurrence was minimised; conversely, both low‐ (1291–2988 m a.s.l.) and high‐ (4022–4588 m a.s.l.) elevation lakes showed reduced richness and elevated co‐occurrence. It shows that key environmental proxies diverged, that is, human activity intensity, temperature and nutrient level declined with elevation, water transparency increased while productivity and environmental heterogeneity peaked mid‐elevations. Temporally, at mid‐elevation Lake Tiancai, richness declined since the 1990s while co‐occurrence, evenness and variability increased, driven predominantly by rising temperature, with rare taxa and specialists accounting for the vast majority of taxon loss. Conclusions Our findings reveal elevation‐dependent biodiversity mechanisms: Human disturbance dominates richness patterns in low‐elevation lakes, while climate warming disproportionately threatens rare and narrowly distributed taxa at mid‐elevations. Critically, an inverse richness‐co‐occurrence relationship persists across spatial (low/mid elevations) and temporal scales, where elevated co‐occurrence signals environmental filtering that constrains local biodiversity. Conservation strategies must, therefore, prioritise protecting heterogeneous habitats to mitigate biotic homogenisation and sustain vulnerable taxa.