Document: BRY-3-52-60

Habitat-specific variation in species interactions in a neotropical stream: The roles of predation and prey settlement rates.

DALEY, B.A.* and A.S.FLECKER

Cornell University, Ithaca, NY 14853 USA ¹

Abstract:
Ecologists are actively investigating variation in species interactions and the processes that underlie this variation across different environmental conditions. We examined species interactions across riffles and pools in an Andean piedmont stream in Venezuela. An enclosure/exclosure experiment was conducted to examine the effects of macroconsumers (fish) and a micrograzer, Petrophila sp.: Pyralidae, on total benthic invertebrate density and algal biomass. Treatments included: 1) Open plot (accessible to the entire fish assemblage); 2) grazing fish enclosure; 3) micrograzer enclosure; and 4) a grazing fish/micrograzer exclosure. Total benthic invertebrate density decreased in open pool plots after 24 h due to heavy fish predation, and remained low throughout the 14 d experiment. In contrast, total benthic invertebrate densities did not differ among other treatments. Algal biomass differed by both treatment and habitat such that micrograzer mortality in open pool plots resulted in an indirect increase in algal biomass. A subsequent cage experiment was conducted to determine if higher mortality of micrograzers in pools compared to riffles was due to differences in predation rates or micrograzer settlement rates. The relative importance of these processes differed according to habitat. Predation rates were higher in pools, but micrograzer settlement rates were higher in riffles. Results suggest species interactions in a diverse stream system vary between habitats, but multiple processes are important in explaining the effects of this variation.

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This abstract is being presented at: 8:30 AM in session:
Oral Session #55: Invertebrates in Streams: Foodwebs.