PARENT SESSION
Oral Session # 91: Biogeography III: Aquatic Communities.
Presiding: B Taylor
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 103.
Community age and species composition: Invasibility and turnover in natural zooplankton assemblages.
Johnson, Michele*,1, Chase, Jonathan1, 1 Washington University, St. Louis, MO
ABSTRACT- The patterns of species composition among communities can give important insights into the process of community assembly. Previous hypotheses regarding community assembly include the achievement of (1) a single equilibrial state (composition determined by a combination of environment and species interactions), (2) multiple equilibrial states (composition determined by environment, species interactions, and invasion history), (3) cyclical equilibrial states (same as 1, except composition changes cyclically through time), and (4) the absence of equilibria where composition is continually in flux (owing to neutral processes such as ecological drift). To distinguish among these four hypotheses, we studied the assembly of zooplankton communities among constructed ponds that varied with age and thus the time for communities to establish. We established natural zooplankton communities from the ponds of different ages in experimental mesocosms and then introduced potentially invading zooplankton species from within the regional species pool. We found that older pond communities were less likely than younger communities to experience species turnover when invaded by species from the region. This pattern, in which older communities appear more stable in species composition when perturbed with invasions from the regional species pool, conforms to concepts that assume that species composition achieves some sort of equilibria through time. In addition, we found that when invaders were rare with respect to the natural community, the community experienced less species turnover then when invaders were common with respect to the natural community. This suggests that species interactions are an important factor in establishing the species composition of communities, and that they appear to have multiple stable equilibria.
Key words: species composition, invasibility, turnover, zooplankton