Drivers of invertebrate community structure in a high-volume Neotropical cave system: a newly recognized subterranean biodiversity hotspot

Understanding how niche-based and neutral processes shape biological communities is a central objective in ecology, particularly in extreme and poorly explored environments such as large subterranean systems. Here, we investigated the mechanisms structuring terrestrial invertebrate communities in the one of the most extensive and voluminous cave systems in South America. Sampling across 56 sectors (30 m²) and 168 quadrats (1 m²) revealed 123 terrestrial invertebrate species. Complementary intuitive searches conducted throughout the cave, combined with standardized sampling, indicated that the system harbors at least 23 obligate cave species, supporting its recognition as a new hotspot of subterranean biodiversity. Total species richness, as well as the richness of non-troglobitic species, increased with resource availability and shelter availability, indicating a strong influence of niche partitioning. In contrast, troglobitic species richness declined markedly with increasing distance from aquatic environments, highlighting microclimatic stability as a key environmental filter. Beta diversity was primarily structured by microclimatic stability and resource availability, whereas geographic distance and cave identity had comparatively minor effects, suggesting that dispersal does not represent a major constraint on species distribution within this highly connected system. Resource gradients promoted species turnover in troglobitic assemblages, while richness differences predominated in non-troglobitic assemblages. Overall, our findings indicate that community assembly in large cave systems emerges from the joint action of environmental filtering and niche partitioning, with responses varying across spatial scales and degrees of ecological specialization. These results reinforce the conservation importance of high-volumnous cave systems as unique environments that harbor highly diverse and specialized biotas.