Sharing the space: coexistence among terrestrial predators in Neotropical caves

The subterranean environment has a set of unique characteristics, including low thermic variation, high relative humidity, areas with total absence of light and high dependence on nutrient input from the epigean environment. Such characteristics promote distinct ecological conditions that support the existence of unique communities. In this work, we studied seven caves in the Presidente Olegário municipality, Minas Gerais state, Southeast Brazil, to determine their richness of predatory species, to understand how they are spatially distributed in the cave and whether their distribution is influenced by competition and/or predation. We carried out five surveys of the caves, with each cave divided into sampling plots. We collected fauna within the plots using a manual search method. The collected animals were fixed in 70% ethanol for later identification. We performed a canonical correspondence analysis to verify the spatial distribution and substrate preference of each species, and selected five species for agonistic interaction testing in the laboratory. We found a great richness of predators in the caves, with 79 species distributed among 22 families of spiders, five families of pseudoscorpions, three families of chilopods, two families of opilionids and one family each of scorpions and heteroptera. Spiders were the most species diverse and abundant of all arthropods we found in the caves. We recorded evidence of competition among some pairs of species but, in general, the spatial distribution of the predatory community in the interior of the caves seems to be unrelated to interspecies competition. The laboratory pairings support our field observations that most species merely share space, rather than exhibiting aggressive or predatory behaviour.