A LIFE-HISTORY TRADE-OFF IN DROSOPHILA SPECIES AND COMMUNITY STRUCTURE IN VARIABLE ENVIRONMENTS

1. Within taxa at the class or family level, the developmental period is often proportional to adult life span. In Drosophila species, a sho rt developmental period increases larval competitive ability. Species with a long adult life, however, may have a better chance to reach new breeding sites in time and space. In another paper (Sevenster & Van A lphen 1993), we presented a model incorporating this trade-off. It sho ws that fast larval developers ('fast species') are dominant when bree ding opportunities are frequent, and that good adult survivors ('slow species') are dominant when breeding opportunities are scarce. Moreove r, the model demonstrates that a fast and a slow species may coexist i n intermediate environments. In this paper we show that data from expe riments and the field support the model. 2. The trade-off between larv al developmental rate and adult survival is established in a guild of frugivorous Drosophila species from Panama. 3. The interval between pr ovisioning with larval food in population cages influences the outcome of competition between a fast and a slow species roughly as predicted by the model. 4. In the field, slow species are more abundant among a dults than among recruits, as is expected from differential survival o f adults and from differential competitive ability of larvae. 5. The g uild composition in the field shifts towards fast species when fruits are abundant, and towards slow species when fruits are scarce. 6. Spec ialized species, which perceive a lower abundance of breeding sites th an generalists, are slower species than are the generalists. 7. We con clude that there is ample evidence that differences in life-history st rategy influence the structure of natural communities in a predictable way and promote the coexistence of species using similar resources.