Beisner, B. E. Dept. of Zoology and Crisis Points Group of the Peter Wall Institute for Advanced Studies, University of British Columbia, beisner@zoology.ubc.ca
Anderies, J. M. Crisis Points Group of the Peter Wall Institute for Advanced Studies, University of British Columbia, anderies@math.ubc.ca

 
A STOCHASTIC MODEL OF PHYTOPLANKTON COMMUNITY STRUCTURE IN FLUCTUATING ENVIRONMENTS
 
In aquatic environments planktonic organisms are subject to periodic nutrient input from various sources and at various frequencies. Competing phytoplankton observe a temporally fluctuating resource base, not a constant one in lake systems that experience periodic deep-water mixing owing to storm and wind events. Although temporal variability in resource supply has been considered as a diversity-promoting mechanism, previous models have concluded that such variability is a weak diversity-promoting mechanism. We have developed a model of competition in environments in which nutrient supply fluctuates in a stochastic manner. In deterministic models of competition, adding a fluctuating resource base leads to only small regions of parameter space in which coexistence occurs. To render our model more representative of the situation in a lake, we incorporated stochastic nutrient pulses with several average frequencies. In order to account for spatial considerations in a simplistic way, demographic processes were also stochastic. We found that in the stochastic model, resource fluctuations dramatically increase the likelihood of coexistence over the deterministic case where competitive exclusion was generally the rule. These results suggest that temporal variability in nutrient supply should be an important mechanism for coexistence among competing phytoplankton in natural systems.
 
Day: Monday, Feb. 1
Time: 02:30 - 02:45pm
Location: Sweeney Center
 
Code: SS01MO0230S