A simulation approach to understanding the processes that structure food webs

A simulation model of food web dynamics, WEB, was constructed and used in Monte Carlo experiments to study the relationship between structure and function in food webs.

Four main experiments were designed using WEB. The first tested the robustness of food web structures at equilibrium to variations in the functional response of predators in the food web to the densities of their prey. It was discovered that a sigmoid functional response did not necessarily facilitate persistence for all species in model food webs as it does in models haying only two trophic levels.

The second experiment clarified the roles of predation and resource-limitation in the process of structuring food webs. In particular a distinction was uncovered between predation and resource control of species selection and the regulation of species densities by predation and resources.

A third experiment studied the influence of productivity on food web structure and function using simulated food webs. The number of supportable trophic levels increased with increased productivity. There were some indications that increasing productivity without allowing higher trophic levels to invade can lead to intense predation pressure on species in the food web.

The final experiment was designed to study the differential successes of generalists and specialists. Experimental results indicated that: (1) the efficiency of predation gained by specializing, (2) trophic position in the food web, and (3) the numbers of prey in the diets of most competitors and predators, could influence the success of a particular species with a given number of prey.

The main advantage gained by using a simulation approach in each of these experiments was the ability to assess the roles played by processes of predation and competition in structuring model food webs. This was accomplished by interpreting the order of extinction events that occurred in the simulations and relating these to the species configurations at equilibrium.