Composition, microgeographic variation, and sexual dimorphism in Caatingas and Cerrado bat communities from northeast Brazil

Abstract

Although the South American tropics canlains the most diverse chiropteran faunain the world, most inklrmation concerning bats from this region is of a taxonomic or distributional nature. Fur- ther. most of our knowledge of Nralropical biology is restricted to locales wnhin mesic predictable biomes. The Brarilian Nonh- east is an extensive tropical semiarid region characterized by climatic unprcdiclability and topographic heterogeneity, yct its fauna has never been studied. An 18 month field study of chi- rapteran populations in Caatingas and Crrrado con~n~unities the Nonheast revealed individual. secondary sexual, and micro- geographic variation in the hat launa. Study sitcs werc restricted in sire to reduce the probability of sampling bats frum different communittcs while intensive monthly sampling regimes werc established to define the faunal composition ofeach community. Dcs-pitc their geographic proximity, thc Caatingas and Cerrado contain strikingly different faunas bath taxonomically and eco- logically. This disparity is most clearly exemplified by thc inscc- tivore gullds in each biame. Two ltypothe~cs are prnposed lo uT account for thc greater di5,ersity of the Caatingas: 1) Large mesic enclaves (serrates) are common in thc Caatingas and probably insulate the fauna from the advcrseeffcctsofclimatic vicissitudes, whereas great spatial hctcrogeneily produces distinct habitats for differential exploitation by different bat specics. and 2) low insect abundance and diversity on the Chapada as well as reduced can- opy complexity within habitats drminishe3 the number of insec- tivorc niches available within thc Ccrrado. Statistical analyses based on 14 entcrnal and I6 cranial mea- surements showed that many species with at least moderate sam- ple sizcs display sexual dimorphism. whereas interdemic varia- tion bctween Caatingas and Ccrrado populations is somcwhat rarer. The applicability of various hypotheses concerning sexual dimorphism in bats is reviewed in light of the observation that females arc larger than males in many bat species. Signihcant geographic variation between adjacent populations of highly mo- bile specics in maintained in many ha1 species in the Brazilian Northeast.