Great Lakes Center Seminar:

"Interactions at the edge of distributions – on the importance of understanding distributions in Great Lakes pelagia"

Dr. Lars Rudstam
Cornell University

Predator-prey interactions depend on encounter rates and therefore on overlapping distributions. I will present two case studies, one from Lake Champlain, the other from Lake Ontario. In the first case study, we show that cannibalism is the major cause of YOY rainbow smelt mortality in Lake Champlain and that cannibalism is better predicted from a measure of experienced density that include spatial overlap than from density of cannibals alone. This has consequences for the seasonal timing of mortality and the effect of an invasive species - the alewife - that arrived to Lake Champlain last year. The other case study is about a mysis shrimp (Mysis relicta), the quantitatively most important predator on zooplankton in Lake Ontario’s offshore pelagic food web. The 5-15 mm long shrimp migrates over 100 m from the bottom towards the surface to feed on zooplankton at night. The importance of mysids as zooplanktivores requires predictions of the whole distribution, not only the mean depth of the population. This is typically not done in optimization models. We have developed a model based on the behavior of mysids to gradients of light and temperature that predicts distributions in the field. This suggests that the predator-prey interactions between zooplankton and mysids occur at the edge of their distributions, and these distributions are affected by the current illumination of the food web associated with decreased nutrient concentrations. The results from both lakes point at the importance of including dynamic spatial distributions in our predictions of effects of predator-prey interactions.

Thursday, November 13, 2008
12:15 p.m.
Location: Classroom Building 106

Students, staff and faculty welcome. Light refreshments will be served.