Does the Cave Environment Limit Functional Diversity? Rethinking Patterns in Oniscidea Assemblages From a Neotropical Karst

ABSTRACT Caves impose restrictive environmental conditions that often promote morphological convergence, especially under permanent darkness. Isopods are successful colonizers of these habitats, yet the processes structuring their biodiversity in hypogean systems remain poorly understood. We tested whether hypogean habitats differ from epigean ones in the standardized effect size of functional richness (SES α) and whether functional dissimilarity is driven by distinct β‐components. We assembled a site × species matrix (54 sites) and a species × traits matrix, standardized traits, and estimated n‐dimensional probabilistic trait spaces (Gaussian‐kernel hypervolumes) using three PCoA axes. Functional α‐diversity was measured as hypervolume size, and pairwise β‐diversity was partitioned into β total , β repl , and β richl . Null expectations were obtained by randomizing the trait matrix, and SES values were computed for α and β metrics. Communities were classified as epigean (Epi), hypogean with troglobites (Hyp), and hypogean without troglobites (HypWT). SES α ranged from strongly negative to strongly positive, with Epi and HypWT showing slightly higher central tendencies than Hyp, but without significant differences among groups. SES β repl was significantly lower and SES β richl significantly higher among groups, indicating reduced functional turnover but amplified richness differences. Trait overdispersion was more frequent in Epi and HypWT sites than in Hyp sites. Taken together, these patterns indicate that isopod communities along the epigean–hypogean gradient are shaped mainly by environmental filtering and an uneven occupation of trait space, rather than simple trait replacement.