CS35 Trophic Dynamics
Date: Friday, June 14, 2002
Time: 8:45:00 AM
Location: Carson A
 
KatechakisA, Aquatic Ecology, Ludwigs-Maximilians-University (LMU), München, Germany, Katechakis@zi.biologie.uni.muenchen.de
Stibor, H, , Aquatic Ecology, Ludwigs-Maximilians-University (LMU), München, Germany, Stibor@zi.biologie.uni.muenchen.de
 
EFFECTS OF PRODUCTIVITY AND OMNIVORY ON THE LENGHT OF LIMNIC PLANKTONIC FOOD CHAINS
image
The absence of a clear answer to the question what limits the lenght of food chains is one of the greatest enigmas in ecology. While there exist several theoretical investigations, experimental data is poor. Nutrient enrichment and omnivory may each be important parameters in determining food chain lenght. We assembled freshwater planktonic food webs consisting of two food chains (green alga - rotifer; bacteria - HNF - ciliate) linked by a terminal predator and manipulated nutrient levels and the presence of omnivorous protozoans. Higher trophic levels (microzooplankton, omnivores and top-predators) persisted only at the highest nutrient levels, suggesting that productivity sets the frame for the theoretically possible maximal food chain lenght. Food webs with omnivores showed increased population oscillations for several food web components. This effect was stronger with rising nutrient levels. The combination of high nutrient levels and the presence of omnivores may thus have a destabilizing impact on the food web leading to shorter food chains (realised food chain lenght) than expected from nutrient conditions alone.