Subterranean 'oasis' in the Brazilian semiarid region: neglected sources of biodiversity

Semiarid regions experience conspicuous seasonal variations, especially related to precipitation. Caves in these areas can be exceptions since they are less affected by dry seasons. In the north of the Brazilian semiarid, there are structurally heterogeneous karst areas with significant speleological potential and several anthropogenic impacts, with a neglected subterranean fauna. Therefore, we aimed to evaluate the influence of caves and external environmental features on the species richness and composition of cave invertebrates of this region. We expected that the caves would have high species richness and endemism, high dissimilarity among spatially discontinuous regions, and caves with water or guano would have greater overall richness and troglobitic species richness than those without water or guano. We collected invertebrates in 40 caves and recorded 416 species from 145 families and 45 orders (38.28 ± 13.88 spp./cave). We identified 57 species with troglomorphic traits, most having narrow distributions, including phylogenetic and/or geographic (oceanic) relicts, suggesting a lengthy and complex evolutionary history. In addition to the faunal dissimilarity among hydrographic basins and caves with or without water, our data indicate the variety of resources, the native vegetation surrounding the caves, the area, and the number of entrances as relevant variables of species composition and richness variation. Caves with water or guano had the highest richness of troglobites. The study area is unique in South America for having such a high concentration of troglobites associated with the presence of karstic aquifers and paleoclimatic changes (including oceanic transgressions and regressions), thus deserving emergency conservation actions.