Effects of ontogenetic niche shifts on the structure of small communities

Background/Question/Methods

The majority of animal species on Earth have a complex life cycle, characterized by distinct shifts in ecological niche during ontogeny. These ontogenetic niche shifts involve changes in resource use, habitat as well as susceptibility to predators. Ontogenetic niche shifts are especially common among species that grow over a substantial range of body size between birth and maturation. They may thus be particularly important in size-structured populations and communities. Recent theory has shown that an ontogenetic niche shift in consumers, which exploit different resources during their juvenile and adult stage, may lead to alternative stable equilibria in a consumer-2 resources system. The consequences of ontogenetic niche shifts for the dynamics of communities involving multiple trophic levels are, however, as of yet unknown. We investigated the effects of an ontogenetic shift in resource use by consumers on the possible equilibria of a community of 2 resources, a single consumer and up to two predator species using stage-structured biomass models.

Results/Conclusions

We show that the ontogenetic shift in resource use of the consumer may result in an emergent Allee effect for a predator that forages on both consumer stages to an equal extent. Over a range of resource productivities the community can hence occur in a stable equilibrium with or without the generalist predator. We furthermore show that an increase in productivity of the resource for juvenile consumers may lead to extinction of predators that selectively forage on these juvenile consumers. Similarly, an increase in productivity of adult consumer resource may drive predators specializing on adults to extinction. Finally, we show that the combination of these two effects may result in mutual facilitation between the two predator species. This means that over substantial ranges of productivities of the juvenile and adult consumer resource, neither of the predator species can persist on its own or can invade a community with only consumers and resources. When together, however, persistence of the two predator species in stable equilibrium with the consumer is guaranteed over the entire range of resource productivities for which they can not survive on their own.