Non‐random assembly and functional trait consistency in tropical diving beetle communities (Coleoptera: Dytiscidae) across Ugandan freshwaters

Abstract Understanding how ecological communities are assembled requires disentangling the relative roles of deterministic and stochastic processes across heterogeneous environments. Tropical freshwater ecosystems remain underrepresented in this context, despite their high biodiversity and vulnerability to anthropogenic pressures. We investigated community assembly mechanisms in predaceous diving beetles (Coleoptera: Dytiscidae) across three ecologically distinct freshwater habitats in Uganda—a papyrus‐dominated wetland, a montane stream–pond system, and a human‐modified wetland. Using standardized activity trapping, functional trait data (body size), multivariate ordination, generalized linear models (GLMs), and null model co‐occurrence analyses, we evaluated patterns of species composition, abundance, and assembly structure. Assemblages showed remarkably similar species richness, diversity indices, and rank–abundance distributions across sites. Detrended Correspondence Analysis revealed moderate compositional turnover (2.3 SD units), indicating partial but not complete species replacement along the primary environmental gradient. A negative binomial GLM indicated that site identity influenced abundance, whereas body size and its interaction with site were not significant predictors, suggesting weakly negative and consistent size–abundance relationships across habitats. Null model analyses rejected competition‐driven exclusion and instead supported species aggregation consistent with habitat filtering, facilitation, or shared environmental responses. Together, these results indicate that Ugandan Dytiscidae assemblages are structured by a combination of broad‐scale dispersal, habitat filtering, and stochastic processes, resulting in resilient community structures across heterogeneous freshwater environments. Our findings highlight the value of functional traits and null models for understanding tropical freshwater community assembly and inform conservation and biomonitoring strategies in rapidly changing landscapes.