Print PageDensity-mediated effects have long been considered the primary driver of community structure. However, non-consumptive effects (NCE) have recently been found to be equally, if not more important in some systems. Most attention on NCE has been empirically focused and specific to dynamics between trophic levels. Far less attention has been paid to understanding the mechanistic role of non-consumptive effects on within trophic level dynamics, such as the coexistence of competitors.
Here we investigate whether behavioral modification of a dominant competitor to the presence of a predator can enable the invasion and persistence of a weaker competitor. Building from 2 to 3 to 4-species modified Lotka-Volterra models we investigate several ways non-consumptive effects may change demographic rates, ultimately changing the relative strength of interspecific to intraspecific competition thereby enabling invasion and coexistence of non-dominant competitors. We model non-consumptive effects as saturating functions of predator density, predator lethality, and effectiveness of prey response versus cost of response, and investigate parameter boundary conditions for invasion and coexistence.
Results/Conclusions
We find non-consumptive effects can influence community dynamics, enable invasion and promote coexistence. Additionally, we find non-consumptive and consumptive effects can vary in strength to yield similar outcomes of invasion and coexistence over a range of parameter values. Based on the parameter space that promotes invasion and coexistence, we discuss what natural systems would be expected to exhibit strong non-consumptive effects and intermediate level of non-consumptive and density-mediated effects.
These models yield insight into the dynamics of simple three and four species food webs, and more generally into the potential importance of NCE as a mechanism driving coexistence in a diversity of systems.
