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Communication at the NABS Annual meeting, Keystone, 2000
(199) MEDIATION OF ALGAL-GRAZER AND GRAZER-GRAZER INTERACTIONS: THE ROLE OF CURRENT VELOCITY.
T. Wellnitz and N.L. Poff. Department of Biology, Colorado State University, Ft. Collins, CO 80523
The strength and outcome of diverse biotic interactions in streams may be constrained by local environmental conditions. Herbivory is an important ecological process and current is a defining feature of streams, yet we know little about how grazer-grazer and grazer-algal interactions vary across current velocity gradients. We investigated the independent and interactive effects of 3 herbivorous insect species (Glossosoma, Baetis and Drunella) foraging on periphyton under 3 current velocities (5, 15 and 35 cm/s) in streamside channels along the upper Colorado River. Two experiments were conducted, one in which herbivore biomass was held constant across 4 species combinations (3 single, 1 three-way), another in which Glossosoma and Drunella biomass were allowed to vary. In each experiment, current velocity had a profound influence on species interactions. In the first experiment, for example, current velocity modified the magnitude and direction of grazer regulation of algal biomass. In the second experiment, current mediated a positive relationship that occurred between Glossosoma growth rate and Drunella density (i.e., facilitation). Facilitation occurred primarily at slow current, was weak at medium current, and was non-significant at fast current. Our results suggest herbivory and herbivore interactions vary dynamically in streams depending on the local current velocity context.
Presented at 9:00 AM on Wednesday, May 31, 2000 in Context Dependency: Role of the environment in shaping species interactions and organizing communities in streams
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