9628969 Heard The goal of this research is to test some long-standing but poorly supported hypotheses about interactions among invertebrates inhabiting temperate streams. Communities of bottom-dwelling stream invertebrates include organisms with several different feeding strategies. "Shredders" feed on large pieces of organic detritus, such as dead leaves and twigs. "Collectors" feed by filtering small organic particles from the water. Because shredders process larger organic material to small particles as they feed, it has been widely assumed that their presence benefits collectors (increases growth and/or survival). However, recent theoretical work suggests that this is only one possibility. Processing of detritus produces particles in the short term, but also removes material that could yield particles later; therefore, the presence of shredders might be detrimental to collectors, particularly over longer time scales. In the present study, experimental manipulations of shredder densities in natural and artificial streams will be conducted to determine the nature of the shredder-collector interaction in a small stream in eastern Iowa. These will be the first complete, direct field tests of the shredder-collector facilitation hypothesis. A third group of invertebrates, called "grazers", feed by scraping algae from surfaces in streams. These animals also produce particles as they feed, and it has also been assumed that grazers facilitate collector growth or survival. This hypothesis will be tested with grazer manipulations in parallel with the shredder experiments. Understanding interactions among stream invertebrates is important because these organisms have ecological and economic importance beyond the local stream reach. For instance, the study organisms are food resources for aquatic and terrestrial animals including birds, bats, and economically important fish species such as trout and salmon. Some collectors (blackflies) are important pests and disease vectors for wildlife and livestock. Finally, these invertebrates are widely used in assessing and managing stream water quality. Results from this study will increase understanding of interactions among species that are central to this important natural community.
