From apparent competition to facilitation, impacts of consumer niche construction on the coexistence and stability of consumer-resource communities

Summary In addition to their direct trophic effects, some consumers have a positive indirect effect on their resource, due to niche construction. A predator can facilitate its prey resource acquisition, through prey transport, or through modifications of nutrient cycling. Other predators defend their prey against other predators, or actively manage it, as in agriculture, which is found in numerous taxa such as humans, but also ants, beetles, fishes and microbes. Here we investigate the ecological consequences of considering such positive effects in a simple two resource–one predator module, in which the consumer has a positive effect on one of the resources. We consider several scenarios, in which the positive effect of the resource is either non costly, ie resulting from a by-product of the consumer phenotype such as nutrient cycling, or costly. The cost either decreases the exploitation of the helped resource or the opportunity to forage the alternative resource. We show that by modifying the trophic interactions in the module, niche construction alters the apparent competition between the resources, thereby impacting their coexistence. We investigate how the intensity of niche construction impacts species coexistence, the distribution of biomass among the three species, and the stability of the community. When niche construction has little or no cost, it leads to higher consumer and helped resource densities, while decreasing the alternative resource density. Alternatively, when niche construction has a strong cost, the alternative resource can increase in density, niche construction thereby leading to the emergence of facilitative interactions among resource species.