PARENT SESSION
Oral Session # 20: Biogeography II: Microorganism and Insect Communities.
Presiding: R Winfree
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 106.

Invasion success and the impact of microorganisms on a resident community.

Price, Jennifer^*,, Hamilton, Robert, Ravit, Elizabeth, Morin, Peter,

ABSTRACT- We conducted an experiment monitoring the invasion success of nine protozoan species into established communities of protozoans and bacteria. We also studied their effect on the resident community. Three invading species represented each of three trophic levels: bacterivores, omnivores, and predators. All of the invaders successfully invaded the resident community, although one species, the predator Didinium nasutum, was rapidly declining by the conclusion of the experiment. Invader success, measured by total biomass of the invading species, was not related to the trophic level of the invader. Predators, however, had the greatest effect on the resident community. By the end of the experiment, only predators had significantly affected any of the resident species in comparison with the control community, which contained no invaders. There was also more variation in the way that predators affected the resident community. Each predator eliminated at least one resident species, but the species driven to extinction differed with the identity of the predator. In contrast, final densities of resident species were similar in treatments with bacterivorous and omnivorous invaders. The biomass of an invading species was not related to its effect on the resident community. Stentor coeruleus, a predator, had consistently low biomass throughout the experiment, but had the strongest effect upon the resident community. Therefore, we conclude that the biomass of a species was a poor predictor of its effect upon other species in this community.

Key words: invasion, protists