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Large-scale experiment showing striking differences in organic matter after

excluding one fish, Prochilodus mariae (left), versus all fish (right).



The aim of my tropical research is to investigate the degree to which a single detritivorous fish species regulates carbon and nitrogen cycling in a tropical Andean stream that contains ~100 fish species in a 2 km river section.  Studying organic carbon flow and nitrogen cycling is important because organic carbon is the main energy source in rivers and nitrogen often limits biological systems and nutrient cycling is an ecosystem service provided by rivers.  I am testing the effects of a dominant sediment-feeding fish, the flannelmouth characin, Prochilodus mariae, on organic carbon flow and nitrogen cycling.  To experimentally test whether this single fish species is a major driver of nutrient dynamics I am using a large-scale approach.  I split the stream longitudinally by installing a 250-meter plastic curtain down the middle.  I exclude only Prochilodus from one side of the curtain using size-selective wire mesh placed at the top and bottom of one side, whereas on the other side all fishes including Prochilodus have access.  My collaborators and I have used this approach to predict how losing Prochilodus from overharvesting, dams, and land-use change will alter ecosystem metabolism, namely heterotrophic respiration, primary production, and organic carbon spiraling (Taylor et al 2006).


Using a nitrogen isotope addition, I have also tested the impact of this single fish species, Prochilodus mariae, on multiple components of the nitrogen cycle. This work is supported by a NSF International Programs Dissertation Enhancement Grant and NSF DEB grant. It has broad significance from both scientific and societal perspectives. For example, it examines the importance of individual migratory species to ecosystem processes, and integrates the often-disparate fields of population ecology and ecosystem ecology. Moreover, this work suggests that a single fish species can be a major driver of ecosystem processes, and thus, small changes in biodiversity can have disproportionately large effects on ecosystem function, even in a tropical stream with more than 75 fish species. For society, this work focuses on a family of migratory fishes that are major protein sources throughout the Orinoco and Amazon watersheds. The threat of losing Prochilodus populations has already been realized in many Andean streams. Documenting their importance to ecosystem phenomena is essential for implementing conservation programs, managing the fishery, and maintaining ecosystem function of Andean piedmont streams.






A sack full of Prochilodus mariae

Local fishermen use cast nets to catch Prochilodus



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