Evolution of Efficiencies and Strategies of Resource Exploitation

Abstract

A logistic model generalized to multiple resources as well as species was used to test ideas about the conditions under which particular efficiencies and strategies of resource use ought to evolve. I hypothesize that obligate generalization and specialization, respectively, are the optimal strategies when the mean ratio of population size to environmental carrying capacity is constantly large or small, but that facultative specialization is optimal when this ratio is variable. Facultative strategists specialize (i.e., use some subset of available resources) when their population sizes are small relative to the environmental carrying capacity, but generalize progressively as this ratio increases. These ideas were evaluated by simulating competition among otherwise identical species with different efficiencies and strategies of resource use, in environments whose resource abundances or rates of supply had coefficients of variation of 0, 1, 10, and 100%. The results confirm expectations in general (e.g., facultative strategists fare better than obligate ones only in variable environments), suggesting that consumers whose resources fluctuate in availability relative to their requirements for them should be facultative. A particularly well—studied resource—consumer interaction permits estimation of model parameters, but the dynamic observations needed to distinguish obligate from facultative strategies are anecdotal. Hence, this theory remains to be evaluated empirically.