PARENT SESSION
Oral Session #36: Animal Community Ecology.
Presiding: S. Simonson
Tuesday, August 6. 8:00 AM to 11:30 AM. Mesquite Room, Radisson.

Contrasting the effects of macro- and micrograzers in a Neotropical stream.

Daley, Bryon^*,1, Flecker, Alexander¹, ¹ Cornell University, Ithaca, NY

ABSTRACT- Macro- and micrograzers in marine and terrestrial systems can have distinct efects on plant assemblages due to differences in body size. Macrograzers also can modify effects of micrograzers via consumption or behavioral modification. Few studies in streams have examined the relative effects of macro- and micrograzers. We used an exclosure/enclosure experiment to compare the effects of the grazing armored catfish, Chaetostoma milesi (Loricariidae)and the invertebrate, Petrophila sp. (Pyralidae), on algal and invertebrate assemblages in an Andean piedmont stream in Venezuela. Treatments included enclosures with Chaetostoma only, Petrophila only, Petrophila and Chaetostoma, and a fish and Petrophila exclosure. Algal biomass was significantly lower in the grazer treatments compared to the exclosure. Iterestingly, algal biomass was lower in the Petrophila treatment relative to the Chaetostoma treatment, but did not differ with both grazers together. The algal response in the Petrophila and Chaetostoma enclosure was not simply due to changes in Petrophila density. In contrast to algal biomass, there was no significant treatment effects on invertebrate abundance or drift density, although interesting trends were observed. These results demonstrate that despite striking differences in body size, some micrograzers in tropical streams can have stronger efects on benthic algal biomass compared to macrograzers.

KEY WORDS: species interactions, streams, Neotropics, grazing