Network structure of bat-ectoparasitic interactions in tropical dry forests at two different regions in Brazil

Network analysis has been used for understanding complex systems in biology for decades. However, scant information is available for networks of antagonistic interactions. The aim of this study was to describe and compare bat-ectoparasite interaction networks in tropical dry forests (TFDs) in the Brazilian Cerrado and Caatinga biomes, which have contrasting environmental conditions and surrounding matrix. Bats and ectoparasites were sampled at six sites in northern and central Minas Gerais State, southeast Brazil. Network connectance, nestedness and number of compartments were compared between regions, as well as bat species richness, abundance and centrality, and ectoparasite specialization. The effect of bat phylogenetic relatedness on the similarity of their associated ectoparasite species was also tested. Bat-ectoparasite networks were nested, connected and highly compartmentalized in TDFs from both regions, with no significant differences in network structure. In addition, host species richness negatively influenced nestedness and connectance, but was positively related to compartment number. These findings are likely related to the high specialization observed for bat-fly species (usually one exclusive parasite species per host), resulting in networks with few interactions. Bat abundance positively affected bat-fly richness, indicating that resource availability is important in determining hostparasite relationships. Finally, phylogenetically related species of bats possessed more similar ectoparasite faunas, which may be associated with evolutionary responses of ectoparasites to escape defensive mechanisms of different bat species. Our results suggest that local bat-ectoparasite interactions are influenced by both ecological factors and evolutionary constraints, but the effects of environmental conditions on network topology deserved further detailed studies.