Niche assembly processes and co-occurrence dynamics of reptile communities across a suite of wetland sites in Uganda

Disentangling the relative roles of environmental filtering, biotic interactions, and stochasticity in community assembly is a fundamental goal of ecology, which we investigate using reptiles as a model system across wetland habitats (28 study sites) in Uganda. We analyzed 142 species from 65 genera and 20 families using standardized Visual Encounter Surveys, supported by pitfall traps and opportunistic observations. Lizards dominated assemblages in abundance and site occupancy, whereas snakes were less abundant but exhibited the highest taxonomic diversity. Species richness showed strong spatial structuring, with northern and western wetlands supporting the highest richness. Vegetation type influenced richness, as savannahs and woodlands hosted fewer species than gallery forests. Rank-abundance curves indicated low evenness in lizards, dominated by a few taxa, versus more equitable abundances in snakes, reflecting differences in niche occupation. Beta diversity was turnover-dominated, suggesting environmental filtering as a primary driver of composition. Null-model analyses revealed taxon-specific co-occurrence patterns: lizard segregation was weak and sensitive to null-model assumptions, whereas snake assemblages exhibited consistently strong segregation, indicating stronger exclusionary processes. Together, these results highlight multi-scale structuring in tropical wetland reptiles, where broad-scale environmental gradients shape species composition, and local biotic interactions further influence community assembly.