Ant rarity and vulnerability in Brazilian Atlantic Forest fragments

The rarity of organisms is related either to a natural origin or human-induced impacts, and rare species are more susceptible to extinction. The Atlantic Forest is an endangered biome with a diverse ant fauna. This study focuses on identifying forms of rarity in ant species recorded in the leaf litter in fragments of the Brazilian Atlantic Forest, as a more acute knowledge of rare species can support more appropriate conservation strategies. To do so, we applied the Rabinowitz method to leaf litter ants, considering data on geographical distribution, habitat specificity, and local occurrence to classify them into "forms of rarity". We then investigated the variation in the composition of forms between phytophysiognomies, and whether environmental variables predict the richness of rare species or not. We also analyzed the degree to which each species is endangered using lists of fauna threatened with extinction from two databases on ants in the Atlantic Forest. In total, we analyzed 242 ant species collected in the forest leaf litter, with 50.4 % classified as "Common", and the remaining 49.6 % presenting some "form of rarity". In general, phytophysiognomies have a similar composition of forms. Environmental predictors influence each form differently. Among all species analyzed (rare and common), seven presented some degree of threat (global, national and state lists). Therefore, conservation strategies must aim at the inclusion of rare ants to ensure their diversity.