Prey Preference by a Top Predator and the Stability of Linked Food Chains

Recent theoretical studies have shown the potential for chaotic dynamics in simple three-species food chains. Most of these studies have focused on linear food chains, although natural food chains are seldom isolated from the surrounding food web. There is a growing awareness that food web dynamics can be strongly influenced by the behavior and movement of predators, energy, and nutrients across ecosystem and subecosystem boundaries. Motivated by observations from lakes, where the pelagic food web is often linked to the littoral food web by mobile predators, we constructed a simple model to evaluate the dynamics of two food chains linked by a top predator with prey preference. Linking the two food chains had no qualitative effect on model dynamics, although it did increase the density of the top predator. Instead, the prey preference of the top predator changed the system dynamics. We found a range of prey preferences that could eliminate chaos, dampen oscillations, and even produce point stability in a previously oscillatory system. The strength of prey preference required to produce a point attractor in a previously chaotic system was positively related to the dimension of chaos (a measure of the complexity of chaos). Our results suggest that, although chaos is possible in food webs, common processes like prey preference reduce the potential for chaos.