Consumers as Maximizers of Matter and Energy Flow in Ecosystems

This article investigates the conditions under which consumers maximize matter and energy flow in ecosystems, using a simple, general, abstract nutrient-limited ecosystem model. The model is analyzed for several functional forms of trophic interactions. The conditions for enhancement of energy flow by consumers are found to be qualitatively the same in all cases. The first and most important condition is that consumers act to accelerate the circulation of matter within the ecosystem; more precisely, the mean transit time of nutrients in the path consumers-decomposers-nutrient pool must be sufficiently smaller than their mean transit time in the path producers-decomposers-nutrient pool. The second condition is that the total quantity of nutrients in the ecosystem must be higher than some threshold value. The third condition is that consumption rate must be moderate. These conditions being usually met, it is likely that consumers as a whole do generally play a role of maximizers of matter and energy flow in stable natural ecosystems.