Overexploitation counteracts top-down control and the paradox of enrichment in simple food chains.

Abstract

Overexploitation, the depletion of a resource by its consumer on a short timescale, is widespread in nature but its general implications for biomass control and community stability are not clear. Most approaches investigating the interactions between trophic levels and variations in biomass patterns or in population dynamics generally ignore overexploitation. Here we use a resource-plant-herbivore food chain model allowing for overexploitation (i.e. the plant can overexploit the resource and/or the herbivore can overexploit the plant). We uncover the conditions under which either type of overexploitation occurs and show that they qualitatively change ecological patterns, mainly by suppressing top-down control when interaction strength is high. When plant productivity increases, top-down control patterns are suppressed above the level when the plant starts to overexploit resources. Similarly, when herbivory intensity increases, top-down control patterns disappear when plants become overex-ploited. Overexploitation also prevents enrichment-driven destabilization by capping the energy fluxes in the community. These findings connect top-down and bottom-up controls in a single framework, and highlight the role overexploitation can play in structuring and stabilizing food chains via the modulation of interaction strengths.