Collaborative Research: Evaluating Species Redundancy in Stream Detrital Processing

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9707500 Covich Detritivores in headwater streams of forested catchments obtain their energy and nutrients primarily from riparian leaf litter input. In the process of shredding and scraping leaf litter they transform microbially conditioned leaves into organic particulates used by downstream suspension feeders. This proposal will investigate the following questions. Do some detritivore species play essential roles in this processing? Are other species redundant in determining the rate of leaf processing and export of suspended particulates to downstream consumers? The loss of one or more detritivore species may alter leaf processing in fluvial ecosystems, yet stream ecologists lack an empirical, stream-based approach for determining if species have unique roles in leaf litter processing or if their interactions are important to other detritivores. The loss of one or more species will not influence overall rates of processing if detritivore species are redundant and have no interactive or unique species-specific role in leaf-litter processing. Alternatively, rates of instream leaf-litter processing will decrease with the loss or replacement of certain benthic detritivore species if these species perform key functions. This research will determine if different detritivore species function either independently of each other, as substitutes or replacements for one another, in a negative, inhibitory manner, or in a positive, facilitative manner. Results of this research in isolated streams will provide data for cross-site comparisons among different species of detritivores from on-going studies of leaf-litter processing at the Luquillo LTER site. In addition, this research will provide insight into the effects of introduced species on ecosystem function in comparison to the functional role on apparently similar, native species.