Sharing the space: variation in morphometric, ecoregional, migratory and reproductive patterns of three sympatric Artibeus species

Bats of the phyllostomid genus Artibeus are primarily frugivorous, and they often are captured carrying the fruits of figs (Ficus spp.) or Cecropia spp. Although two or three species of Artibeus (sensu stricto) are found sympatrically in many regions of the Neotropics, little is known about the potential competitive interactions of these congeners in areas of sympatry. Competition might occur for food, roost sites, or other resources, and might be expressed as spatial or temporal partitioning in feeding or reproduction, as increased displacement of feeding- or foraging-related characters, or as some combination of these factors. These effects might be more pronounced near the distributional limits of the species, where resources might be more limited (both in abundance and diversity), and more patchily distributed. Three species of Artibeus (A. fimbriatus, A. lituratus, and A. planirostris), are at or near their southern or south-western distributional limits in Paraguay. Previous analyses in Paraguay have determined that A. lituratus and A. planirostris are migratory, with A. lituratus being most abundant during the wet season (October–February), and A. planirostris in the variable season (March–May). Artibeus fimbriatus and A. lituratus are relatively more abundant in the Atlantic Forest ecoregion; and A. planirostris in the Cerrado. In this study we examined morphometric variation in wing and craniomandibular characters, as well as reproductive patterns, to further explore the potential niche partitioning along these dimensions that may reduce competition for resources. We tested for morphometric differences among the species, and for geographic and secondary sexual variation in each of the three species. Both wing and craniodental characters vary significantly among species. Artibeus fimbriatus exhibits sexual dimorphism in only one cranial character, and A. lituratus shows sexual dimorphism in three craniodental characters and in all wing characters, whereas A. planirostris is not sexually dimorphic in any character. Weak geographic variation was found in craniodental characters in A. planirostris, and in wing characters in the other two species. Differences were also encountered in the three species’ morphometric responses to temperature and precipitation parameters. Evaluating these differences in morphometric patterns in the context of ecoregional and seasonal associations, migratory status and reproductive patterns, we conclude that the three species mitigate competitive pressure through a complex partitioning of available niche space.