PARENT SESSION
Poster Session 19: Biodiversity
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of biodiversity on community production change over the course of succession: A microcosm study with freshwater algae.

Weis, Jerome^{*,1, 2}, Cardinale, Bradley^{1, 2}, Forshay, Kenneth², Ives, Anthony², ¹ University of California-Santa Barbara, Santa Barbara, CA, 93106² University of Wisconsin-Madison, Madison, WI, 53706

ABSTRACT- The number of studies examining how species diversity impacts community productivity has increased considerably over the past decade as concern about global loss of biodiversity has intensified. Research to date has done much to articulate the hypothesis that species diversity can affect important aspects of community functioning. Yet, because most experiments have been limited in spatial and/or temporal scope, it is somewhat unclear how robust empirical patterns are likely to be. Using a model system of freshwater primary producers with short generation times, we explored how the effect of species diversity on community production changes through successional time. We manipulated the diversity of three species of green algae in laboratory microcosms and then measured the production of community biomass as well as each species population size over a 33-d period. The slope relating community biomass production to species diversity was zero at the beginning of the experiment (due to the substitutive experimental design used), was significantly positive during intermediate time scales, and then returned to zero by the end of the study. Thus, effects of species diversity on biomass production were ephemeral in this system, only observed at intermediate time scales. Analyses of relative population sizes suggest that species tended to do better in poly- vs. monocultures during intermediate time periods, perhaps due to lower intraspecific competition. Yet, in later stages of succession when interspecific competition was more pronounced, species tended to perform worse in polyculture than expected from population sizes in monoculture. While our study over-simplifies many important biological details, the results serve as qualitative support for recent theoretical predictions that both the form and magnitude of the relationship between biodiversity and production vary throughout community succession as interactions alter species performances.

Key words: species richness, ecosystem functioning, primary production, succession