Biological Disturbance and the Organization of Neotropical Stream Communities

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9306639 Flecker Neotropical streams contain diverse and abundant assemblages of fishes, some of which process large volumes of sediments. The proposed research will examine the impacts of fishes as sources of biological disturbance in neotropical stream communities. Preliminary studies indicate that biological disturbance of sediments by fishes has strong consequences that propagate widely through riverine food webs. Three hypotheses about the role of biological disturbance will be addressed: 1) biological disturbance generates resource patchiness by modifying sediment distributions, 2) biological disturbance maintains species diversity by generating a dynamic mosaic of resource states, and 3) detritivorous fishes are keystone species whose presence strongly modifies food web interactions. These objectives will be examined through a series of observational and experimental field studies conducted in the Andean piedmont of Venezuela. A detailed analysis of spatial heterogeneity of sediment accrual patterns will be undertaken from a patch dynamics perspective. Patch characteristics over different spatial and temporal scales will be quantified using methods employed for the analysis of landscapes. These data will be linked with detailed observations and experimental exclusions of fishes at different spatial scales. The influence of biological disturbance in maintaining species diversity will be manipulated and changes in species diversity patterns will be assessed. The role of detritivirous fishes as keystone species in Andean streams will be examined by selectively excluding detritivores. %%% Findings from this study will contribute to our limited understanding of factors organizing neotropical stream communities. This research will integrate sediment animal relationships into a stream community context. Results will indicate whether human impacts on detrital feeding fishes form overexploitation and impoundments may be manifested throughout stream food webs. ***