Little is known about the role of predators in tropical rivers. This study will examine predator prey relationships in a series of Venezuelan streams, where a wide range of predation regimes are found in close proximity. In order to investigate the direct and indirect effects of predators on mayflies (Order:Ephemeroptera), a series of comparative studies will be conducted between streams that range from naturally fishless to others containing > 60 fish species. Direct effects of predators will be examined by performing field enclosure/exclosure experiments. Field experiments will be coupled with data on mayfly drift, predator numbers and diet, to determine if the efficacy of predators in controlling prey abundance differs according to predator density and/or prey recolonization potential. Indirect effects of predators will be examined in several contexts. Diel patterns of mayfly drift and activity on stone tops will be compared between sites. Cinematography will be used to explore the importance of predators in determining both when and where mayflies forage, and the effects of predator harassment on foraging efficiency. Findings from this research will have bearing on general questions concerning the significance of predation in structuring lotic systems and whether the role of biotic interactions differs between tropical and temperate systems. Professor J. D. Allan and doctoral candidate A. S. Flecker are well qualified to conduct the investigation which will entail significant logistic and scientific challenges. The ecology of neotropical rivers is an important area for ecological research.
