Evolutionary strategies and nutrient cycling in ecosystems

We have previously shown that the presence of a consumer in an ecosystem model at ecologically stable equilibrium (ECSE) results in smaller energy and nutrient flows through the system compared to one without a consumer. Here we extend this analysis to examine energy and nutrient flows, and the density and number of species in ecosystems at evolutionarily stable equilibrium (EVSE). To implement the analysis, we first clarify the difference between ECSE and EVSE, and extend the idea of evolutionarily stable strategies as implemented to biological communities to include the non-animated parts of the ecosystem. In a game theoretic sense, this is equivalent to adding external inputs to the game. EVSE solutions of our model ecosystem resulted in frequently observed trends. For example, of two competing producers, one has smaller density, grows faster, is more nutritious to the consumer, and cycles nutrients faster than the other. In both kinds of ecosystem conditions (ECSE and EVSE), adding producer species to a system with a consumer and producer increases the flow through the ecosystem. We also show that a consumer with a high ratio of return of nutrients to the decomposer compartment compared to the losses to the ecosystem from the consumer compartment cannot co-exist with producers at EVSE. At EVSE, the presence of a consumer increases energy flows compared to systems without a consumer, in contrast to a system at ECSE, where the presence of a consumer decreases rates of energy flow. Finally, we interpret the dynamics of the strategies in the context of periodic input to the ecosystem. We show that strategies can be out of phase, thus enabling, for example, species to exploit a resource more (or less) efficiently at different times.