Beyond species diversity: Functional responses of cave arthropods to microclimatic stability and structural complexity

Abstract Understanding how microclimatic conditions and habitat heterogeneity shape community structure, and the underlying assembly processes is essential for explaining biodiversity patterns and predicting future shifts. Yet, the effect of natural microclimatic gradients, such as those from cave entrance to deeper zones, on species assemblages, remains poorly understood. These gradients, defined by shifts in temperature, humidity and light, are coupled with fine‐scale habitat heterogeneity shaped by structural cave features. Because habitat heterogeneity can buffer climatic change, we examined its role alongside the microclimatic gradient in structuring community assembly processes. We sampled 160 units across eight caves and quantified the abundances of species from 11 arthropod orders belonging to seven classes, as well as the distributions of eight functional traits related to morphology, ecology, activity, feeding and subterranean specialization. Species diversity was characterized using both species richness and Simpson's diversity index. We analysed within‐community trait dissimilarity using Rao's quadratic entropy index and community‐weighted means (CWMs) with specifically designed null models. Species richness declined with increasing microclimatic stability (near‐constant temperature and saturated humidity), while Simpson diversity increased with habitat heterogeneity. CWMs of traits such as body size and eye regression shifted along the microclimatic gradient, with larger‐bodied, more regressed‐eye species dominating under harsher conditions. Locomotion traits showed a nonlinear response to habitat heterogeneity, with trait divergence peaking at intermediate levels of structural complexity. These findings demonstrate that microclimate and habitat heterogeneity function as distinct environmental filters, shaping community trait composition through both convergence and divergence. These results underscore the importance of fine‐scale environmental variation in shaping subterranean communities and highlight caves as natural laboratories for predicting biodiversity responses under climate change.