A DESCRIPTIVE AND ANALYTICAL STUDY OF 4 NEOTROPICAL DROSOPHILID COMMUNITIES

Drosophilid communities living in four different physiographical regio ns of the state of Rio Grande do Sul (27 degrees/34 degrees S; 49.7 de grees/57.5 degrees W), Brazil, were analysed. Ignoring cosmopolitan sp ecies, this is about the southern limit of the majority of typically n eotropical Drosophila species distribution. Numerical fluctuations of the most frequent species populations from each place were investigate d in relation to climatic data and trophic-resource availability. Of t he four locations studied, Turvo is remarkable for being an enormous e cological reserve covered with subtropical perennially rainy forest, a nd for having stable weather conditions. Guaiba, on the other hand, is a more climatically unstable place, with unpredictable and more scarc e resources. In Turvo, the community structure is shaped by the domina nce of Drosophila willistoni and a low species diversity throughout th e year. Low average niche-breadth and niche-overlap indices have also been found at feeding and breeding site levels. Guaiba showed the high est species-diversity levels and was better exploited by D. simulans, a cosmopolitan species with a well-known colonizing capacity. High nic he breadth and overlap indices were characteristic for most species at this place. Results are discussed in the light of the communities' sp ecies composition and of environmental factors.