Intra-specific competition influences the rate at which individuals can acquire resources. Mutual interference is a measure of this effect, and it has been incorporated into a variety of functional responses. Interference is usually measured as the slope of the relationship between the log of some resource uptake rate or energy expenditure and the log of density or population size. Interference may take on values from about 0 to -1, but a long-running debate between proponents of prey-dependence and ratio-dependence has focused on the reasons that interference should be either 0 or -1, rather than intermediate. We conduct a literature review to draw a broad picture of interference as found in nature, and we present a new form of scaling to provide theoretical linkage between resource consumption patterns, population level behavior, and competitive dynamics. We use a simple consumer-resource model to illustrate these connections.
Results/Conclusions
The literature review revealed that measured values of mutual interference are mostly intermediate, and are rarely the 0 or -1 assumed by either prey-dependent or ratio-dependent theory. We develop resource-density scaling theory that combines the resource-sharing mechanism of ratio-dependence with an explicit measure of behavioral interactions, illustrating why most values of mutual interference should in fact be intermediate. We argue that such intermediate values may be characteristic for a population in a given context, with impacts on population dynamics and outcomes of consumer-resource relationships. Model results show that greater mutual interference leads to lower per-capita uptake rates as well as lower population-level resource use, which in turns raises the unused portion of resources in the environment. This illustrates that competitive ability, or R*, is driven in part by mutual interference. Our suggestion that mutual interference is a characteristic that links individual resource uptake patterns to community dynamics contrasts with recent suggestions that levels of interference should shift from 0 to -1 as a population grows, setting the stage for future work to determine if interference is “characteristic” or “shifting”.