PS 78-53 - An observational and theoretical study of trait dynamics in a seasonal, freshwater phytoplankton community

Friday, August 12, 2011
Exhibit Hall 3, Austin Convention Center
Elizabeth Miller, W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI

Seasonal succession in freshwater phytoplankton communities is a phenomenon that has fascinated ecologists for nearly a century. We have taken a trait-based approach to describe the trait dynamics in this system, developing a new method of parallel trait assays to quantify species traits through out the season.  We estimate light, nutrient, and temperature growth responses along with cell size, maximum growth rate, and grazer resistance for the most abundant phytoplankton species in the community several times throughout the season. We combine these traits with fitness estimates obtained from weekly community counts to construct a trait to fitness mapping for each weekly set of environmental conditions.  This mapping is a quantitative tool for analyzing the dynamics of community traits as well as studying tradeoff relationships between traits. In addition to the observational study, we constructed a dynamic model of phytoplankton succession in a seasonal environment by imposing a tradeoff between competitive ability and grazer resistance.


These data show qualitative differences in the trait distribution of the phytoplankton between the spring bloom and the summer stratification period.  They also suggest a tradeoff between grazer resistance and nutrient uptake ability. We compare the results of this observational study to the predictions of the model and find a similar shift in allocation to competition or grazer resistance. This approach illuminates the factors controlling the seasonal shifts in phytoplankton assemblages. The method of parallel trait assays is also a new and useful way to quantify the trait distribution in diverse communities especially ones with unfamiliar or previously uncultured members.

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