Beneath the canopy, beneath the ground: how surface microhabitats shape cave communities

Ecosystem dynamics are shaped by spatial and temporal fluctuations in resource availability and species composition across the landscape. Caves exemplify this interconnectedness, as they rely on allochthonous inputs and surface climatic conditions, fostering communities composed of viable populations from both surface and subterranean habitats. Consequently, effective management and conservation of subterranean environments require the protection of adjacent surface ecosystems, a particularly urgent need in the Amazonian ferruginous hills, where mineral exploitation poses a significant threat. In this context, we investigated how vegetation cover and environmental variables influence the distribution of surface and subterranean fauna, and which factors should guide conservation strategies. We sampled six caves and ten epigean transects around each, encompassing both ombrophilous forest and canga (savanna over ferruginous crusts). Environmental structure variables were recorded for all transects. Significant differences were detected between forest and canga in terms of vegetation structure, microclimate, species richness, and community composition. Species most similar to those found in caves were associated with forest leaf litter, particularly in transects closest to cave entrances. Leaf litter depth emerged as a key factor facilitating faunal overlap between surface and subterranean habitats, likely by providing microhabitats with stable temperature and humidity. In contrast, faunal similarity in canga occurred only under specific conditions, namely, milder temperatures, deeper litter layers, and increased canopy cover. Our findings demonstrate that cave-dwelling species in Amazonian ferruginous systems also inhabit adjacent forest environments, which should be prioritized for conservation.