PARENT SESSION
Oral Session #7: Aquatic Ecology: Stream ecosystems. Presiding: T. Ehlinger.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Consequences of detrital heterogeneity for stream invertebrates: Results from a simulation analysis and field experiment.
Swan, Christopher1, Palmer, Margaret1, Nelson, Karen1, 1
ABSTRACT- Allochthonous inputs of detritus can influence both the structure and functioning of food webs. Such resource subsidies can increase the production of consumers, creating more abundant prey for predators. For example, energy demands of temperate streams are met by terrestrially-derived (riparian) leaf litter that enters the system during leaf-fall. While the effects of resource subsidies on food webs have received considerable study, the effect of resource heterogeneity in these subsidies remains untested. Given that leaf litter degrades at different rates depending on tree species, and that stream detritivores are known to track litter "quality", we performed a simulation analysis of temporal invertebrate dynamics. We culled data on litter decomposition rates from the literature and applied a colonization regime that reflected the availability of the litter resources. By randomly choosing combinations of riparian litter sources, we were able to derive a relationship between resource heterogeneity (i.e., litter species richness) and invertebrate abundance through time. The results indicate that if more species of litter are available for colonization by invertebrates, invertebrate abundances vary less over time. This result was employed as a null model for experimental manipulations of leaf pack composition in a Piedmont stream. Our results suggest that increasing levels of riparian tree diversity may, via variation in the quality of litter inputs, impart stability to the invertebrates who in turn are prey for larger predators (i.e., fish).
KEY WORDS: streams, riparian, litter, invertebrates