A Commensal Consumer-Induced Mediation Effects on Resource–Consumer Interactions

Abstract

A general view of resource–consumer interactions is that resource intake by the consumers reduces the growth rate of resource population but it leads to an increase of consumer population. This view is proficiently interpreted with the classic Lotka–Volterra model that successfully describes the effects of changes in consumption rates due to changes in resource and consumer population densities. These effects are resulted in perpetual oscillatory dynamics of both the population densities, and the extent of the effects for given initial densities is measured by the oscillating frequency determined by the model parameters. But in many ecosystems, it has often observed a steep decline and delayed recovery in resource population that cannot be explained by the traditional Lotka–Volterra model. Foraging habits and behaviors of a consumer population may facilitate others, those usually do not affect them directly, to feed on the same resource and then to reproduce successfully. Such commensal consumers (facilitated population) can heavily influence the rate of resource exploitation and thereby affect the usual resource–consumer cycles. While involving such commensal consumer-induced effects, called here commensal mediation, into the Lotka–Volterra type models, it shows that the commensal mediation can have stabilizing or destabilizing effects on resource dynamics depending on the strength of interactions and the conditions in which the interactions occur. In the natural ecosystems where the growth rate of resource population depends on its own density even in absence of consumers, the commensal mediation provides a destabilizing effect on resource dynamics; increasing commensal population density increases the amplitude of resource fluctuations and the time laps from one peak to the next. On the other hand, in the managed ecosystems where the growth rate of resource population is expected to be maintained at a constant level in absence of consumers, the commensal mediation provides stabilizing effect at a certain condition; with a given restriction on the consumer population, decreasing mortality of the commensal population can stabilize the resource population dynamics at a stable, steady-state. Moreover, while the resource population experiences saturation effect, resource–consumer interactions with the commensal mediation exhibit a range of dynamical behaviours starting from stable equilibrium, then damped oscillation, to limit cycles as the resource carrying capacity increases from a critical level. In addition, commensal mediations with both controlling facilitator consumer population and resource harvesting are analyzed separately and the results are discussed for some exemplified managed and natural ecosystems.