Exploitation in model food chains with mechanistic consumer-resource dynamics

Abstract

This study uses population dynamical models that explicitly incorporate mechanisms of competition and predation to examine trophic regulation in food chains containing plants, herbivores, and carnivores. The mechanisms include exploitative and interference competition for time and energy and time- and energylimited predation rates. The various mechanisms are combined in consumer and resource equations to explore how food chain structure varies across gradients of primary productivity. When consumers are limited by exploitative competition for energy, all trophic levels should exist over the entire productivity gradient. When consumers in one or more trophic levels are limited by feeding time and interference competition, there will be threshold levels of productivity before a trophic level can be added to the food chain. The value of the threshold will depend on the magnitude of consumer energy requirements relative to environmental productivity in an area. In all cases, consumer and resource densities should always increase as productivity increases. In general, top down control of food chain dynamics by carnivores, as opposed to bottom up control by nutrient inputs, will be most dominant over low to moderate productivity levels. I show that mechanistic models can produce a broader range of food chain dynamics than traditional Lotka-Volterra consumer-resource models.