Aquatic-Terrestrial Subsidies in a Neotropical River

The importance of spatial subsidies in food web dynamics has become increasingly acknowledged, yet there remains relatively little work in tropical rivers on this topic. In January 2004, I was afforded the opportunity to work with Alex Flecker (Cornell University), Brad Taylor (University of Wyoming), and Bob Hall (University of Wyoming) in Río Las Marias, Venezuela. Their research program is directed at understanding carbon and nitrogen budgets of the river, especially with regard to the abundant migratory algivore/detritivore, the coporo Prochilodus mariae. In January 2004, we divided Las Marias into two sides (see photo) and removed coporo from one of the sides. Then, using labeled N15, we examine how removal of the coporo alters nitrogen dynamics in the system. This project is especially important since the intense fishing pressure has significantly reduced populations of coporo in Andean Piedmont streams, altering nutrient cycling and ecosystem function.

I am taking the lead one sub-component of this project, specifically the aquatic-terrestrial linkage in the form of emerging aquatic insects. Using the labeled N15 tracer, we will be able to assess which terrestrial predators are feeding on the emerging insects. I am especially interested in spiders that are concentrated along the river shoreline, exploiting the high abundance of emerging insects. The importance of the aquatic-terrestrial link will be evaluated across spider species, habitats, and within the context of the coporo stream-scale manipulation.

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