Document: ROB-3-48-38

Relating organic matter flow with experimentally measured interaction strength between two benthic grazers and algae.

HALL, R.O.*

University of Wyoming, Laramie, WY 82071 ¹

Abstract:
Interaction strength can be estimated based on consumption rates of prey taxa and prey numbers; these estimates can correlate with experimentally measured interaction strength in rocky intertidal communities. In this study I compared organic matter flow with interaction strength between two benthic grazers and their epilithic diatom resources in a stream at Hubbard Brook Experimental Forest. Using bioenergetics approaches I estimated consumption rates of algal biomass as a whole and of two species of common diatoms by two benthic grazers: Heptagenia, a mayfly, and Glossosoma, a caddisfly. At the same time I manipulated these grazers to experimentally measure their impact on algae using in-stream cages. There was a significant positive relationship between modeled and measured interaction strength for total algal biomass (r²=0.60) and for one common diatom, Tabellaria (r²=0.81) using both benthic grazers. This relationship was much weaker for the other common diatom, Eunotia. Though modeled interaction strength could predict measured interaction strength, modeled estimates were always higher than measured ones: Five times for algal biomass and about 250 times for Tabellaria, which implies that grazers should impact algae much more than they actually did. This result is possible because diatom populations may be turning over several times during the two-week experiment. Experimentally measured interaction strength can be predicted from interaction strength estimated based on consumption rates, but future studies should address time scales of resource turnover.

Keywords: food webs, interaction strength

This abstract is being presented at: 9:30 AM in session:
Oral Session #37: Phytoplankton.