Theoretical Ecology

Hurtado, Paul; Hall, Spencer; Ellner, Stephen

doi: 10.1007/s12080-013-0208-2pmid: N/A

Nonhost species can strongly affect the timing and progression of epidemics. One central interaction—between hosts, their resources, and parasites—remains surprisingly underdeveloped from a theoretical perspective. Furthermore, key epidemiological traits that govern disease spread are known to depend on resource density. We tackle both issues here using models that fuse consumer–resource and epidemiological theory. Motivated by recent studies of a phytoplankton–zooplankton–fungus system, we derive and analyze a family of dynamic models for parasite spread among consumers in which transmission depends on consumer (host) and resource densities. These models yield four key insights. First, host–resource cycling can lower mean host density and inhibit parasite invasion. Second, host–resource cycling can create Allee effects (bistability) if parasites increase mean host density by reducing the amplitude of host–resource cycles. Third, parasites can stabilize host–resource cycles; however, host–resource cycling can also cause disease cycling. Fourth, resource dependence of epidemiological traits helps to govern the relative dominance of these different behaviors. However, these resource dependencies largely have quantitative rather than qualitative effects on these three-species dynamics. Given the extent of these results, host–resource–parasite interactions should become more fundamental components of the burgeoning theory for the community ecology of infectious diseases.

Liu, Rongsong; DeAngelis, Donald; Bryant, John

doi: 10.1007/s12080-013-0210-8pmid: N/A

A tradeoff between energy gain from foraging and safety from predation in refuges is a common situation for many herbivores that are vulnerable to predation while foraging. This tradeoff affects the population dynamics of the plant–herbivore–predator interaction. A new functional response is derived based on the Holling type 2 functional response and the assumption that the herbivore can forage at a rate that maximizes its fitness. The predation rate on the herbivore is assumed to be proportional to the product of the time that the herbivore spends foraging and a risk factor that reflects the habitat complexity; where greater complexity means greater interspersion of high food quality habitat and refuge habitat, which increases the amount of the edge zone between refuge and foraging areas, making foraging safer. The snowshoe hare is chosen as an example to demonstrate the resulting dynamics of an herbivore that has been intensely studied and that undergoes well-known cycling. Two models are studied in which the optimal foraging by hares is assumed, a vegetation–hare–generalist predator model and a vegetation–hare–specialist predator model. In both cases, the results suggest that the cycling of the snowshoe hare population will be greatly moderated by optimal foraging in a habitat consisting of interspersed high quality foraging habitat and refuge habitat. However, there are also large differences in the dynamics produced by the two models as a function of predation pressure.

LaBar, Thomas; Campbell, Colin; Yang, Suann; Albert, Réka; Shea, Katriona

doi: 10.1007/s12080-013-0211-7pmid: N/A

The recent decline in pollinator biodiversity, notably in the case of wild bee populations, puts both wild and agricultural ecosystems at risk of ecological community collapse. This has triggered calls for further study of these mutualistic communities in order to more effectively inform restoration of disturbed plant–pollinator communities. Here, we use a dynamic network model to test a variety of translocation strategies for restoring a community after it experiences the loss of some of its species. We consider the reintroduction of extirpated species, both immediately after the original loss and after the community has reequilibrated, as well as the introduction of other native species that were originally absent from the community. We find that reintroducing multiple highly interacting generalist species best restores species richness for lightly disturbed communities. However, for communities that experience significant losses in biodiversity, introducing generalist species that are not originally present in the community may most effectively restore species richness, although in these cases the resultant community often shares few species with the original community. We also demonstrate that the translocation of a single species has a minimal impact on both species richness and the frequency of community collapse. These results have important implications for restoration practices in the face of varying degrees of community perturbations, the refinement of which is crucial for community management.