Ants of the Caatinga: Diversity, biogeography, and functional responses to anthropogenic disturbance and climate change

Despite the outstanding diversity and ecological relevance of ants in most terrestrial ecosystems, current knowledge of the ants of the Caatinga is still incipient. This chapter offers an overview covering the diversity, taxonomy, biogeography, and functional composition of the Caatinga ant fauna, and a synthesis on ant response to chronic anthropogenic disturbance and increased aridity. We compiled a database consisting of 572 presence-absence ant records and 276 ant species from 37 localities in the Caatinga. As expected, most of the Caatinga has not been intensively sampled for ants, with the intensive sampling that has been conducted revealing high rates of species turnover across localities. Most ant species recorded in the Caatinga are widely distributed in other biomes, especially in Cerrado, and few species can be considered endemic to the Caatinga. Thus, the Caatinga ant fauna appears to represent an impoverished subset of the Cerrado's fauna. Such a reduced endemism and the occurrence of a highly depauperate ant fauna at a regional level contrast to the diversity patterns exhibited by the Caatinga flora and other faunal groups. Significant changes in ant taxonomic and functional composition in response to human disturbance are observed, with a predictable winner-loser replacement. Disturbance winners consist of generalist species exhibiting wide environmental tolerances and those inhabiting open habitats (Opportunists and Dominant Dolichoderinae). Highly specialized species are disturbance losers (Specialist predators). Aridity also affects both species occurrence and functional-group composition of local assemblages. Since several ant species and functional groups are sensitive to increasing disturbance and aridity, ant-mediated ecological services are already threatened in the Caatinga biota.