Local and Seasonal Variations in Relative Frequencies of Species of Drosophila in Brazil

Abstract

Samples of Drosophila populations were taken in 35 localities in 17 bioclimatic regions of Brazil. The technics of collecting consisted in attracting the flies to bait of fermenting banana and procuring them on natural bait of fallen fruits, flowers, or other substances. Samples taken at distances even as small as 10-20 m. from each other often contained different relative frequencies of various species of Drosophila Drosophila populations thus form nuclei of high and low population densities. Some spp. tended to form discrete nuclei, and others to be distr. relatively more uniformly. Spp. of Drosophila differ in food preferences, and some spp. are more specialized than others. Repeated collecting within a locality disclosed the occurrence of changes in relative frequencies of different spp. from month to month. It is an open question to what extent these changes are cyclic and how regularly they are repeated in different yrs. Temporal changes occurred both in regions in which dry seasons alternated with wet ones and in regions which had relatively uniform superhumid tropical climates. Tropical faunas of Drosophila are richer in spp. than temperate or cold zone faunas. Within the tropics, rain forests have richer faunas than do more arid regions. The richness of tropical faunas and floras is considered to represent an adaptive response of the living matter to the diversity of habitats available in most tropical environments.