Ratio-Dependent Predation

Ecology 73:1536-1543 (1992)

Consequences of Ratio-Dependent Predation for Steady State Properties of Ecosystems

Lev R. Ginzburg
Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794

H. Resit Akçakaya
Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, USA

Abstract  Ratio-dependent and prey-dependent models of trophic interactions make very different predictions about the steady state (equilibrial) properties of ecosystems, such as the response of equilibrium abundance and biomass of organisms in each trophic level to increased primary productivity or nutrient input. Prey-dependent theory predicts alternating positive, negative and zero responses of trophic levels to increased productivity, whereas ratio-dependent theory predicts proportional increase in all trophic level biomasses. We analyzed data on the nutrient input and the biomasses of phytoplankton, zooplankton and fish across lakes to distinguish between ratio-dependent and prey-dependent models. The results show parallel increases in all trophic levels as a result of increased nutrient input, demonstrating that natural systems are closer to ratio-dependence than to prey-dependence.