Coexistence of multiple food chains in a heterogeneous environment: interactions among community structure, ecosystem functioning, and nutrient dynamics.

A model is developed and analyzed for a nutrient-limited ecosystem containing an arbitrary number of parallel plant-herbivore-detritus food chains in a heterogeneous environment, with a view to exploring interactions among community and ecosystem processes. Physical properties of the environment and functional properties of the entire ecosystem such as nutrient supply, transport, and recycling are shown to exert a profound influence on the composition, diversity, and assembly of the biological community. Community structure as well as the physical properties of the environment in turn affect ecosystem functions such as nutrient and energy flow. In particular, the rate of nutrient transport in the physical medium plays a critical role in competition and coexistence among food chains. The potential for coexistence decreases continuously as the nutrient transport rate increases in food chains with donor-controlled or no herbivory, while it increases continuously or is greatest at an intermediate value of the nutrient transport rate in herbivore-controlled food chains. On the other hand, energy flow generally increases with the rate of nutrient transport. Herbivory also exerts a significant, predictable influence on energy flow and coexistence among plants and food chains.