In the present study, I described the organization of a Neotropical bat assemblage, and tested whether this organization was variable in time. In an Atlantic Forest reserve in southeastern Brazil bats were captured monthly with mist nets over 4 years, and individuals were classified into guilds. I analyzed only leaf-nosed bats, and observed that guilds of fruit-eating bats dominated the assemblage. This pattern was repeated across months and years. However, among frugivores, canopy and understory guilds peaked during different months, but in both cases during the rainy season, while variation among habitat-opportunistic species was not explained by rainfall. The most reliable ecological service delivered by phyllostomid bats in the area is seed dispersal, although other services may be also important in particular seasons. My results suggest that the observed patterns of temporal species turnover are related to the abundance of preferred food items.