The effect of the risk of infectious disease on habitat selection

Background/Question/Methods

When animals have a choice of habitats in which to reside, the risks and benefits in each patch must be taken into account in order to arrive at a decision. This choice is often assumed to be one that maximizes individual fitness. When balancing resource quality with competition for resources, Ideal Free Distribution (IFD) theory predicts input matching, a spatial equilibrium in which the distribution of the population over the spatial landscape matches the distribution of resources. Field data and experiments commonly find undermatching, where the higher quality patch(es) are underused compared to IFD predictions. Additional risks, such as predation or kleptoparasitism, have been incorporated into habitat selection theory and can change equilibrium spatial distributions. We investigate the effect of the risk of infectious disease in habitat selection, and whether it may play a role in explaining observed undermatching in data.

We consider a two patch Susceptible-Infected-Recovered differential equation model, where individuals choose a patch at birth and remain there for life. We assume the probability of choosing the higher quality patch is a heritable trait and define fitness to be the total lifetime reproductive success of an individual. Infection by disease may lower fecundity, increase mortality, or both. We calculate the optimal fraction of the population choosing the higher quality patch as well as the corresponding observed fraction of the population at equilibrium and compare these values to IFD predictions.

Results/Conclusions

We find incorporating the risk of infectious disease into habitat selection models leads to undermatching, while overmatching is never predicted. Our model allows for vertical transmission of the disease, recovery, and inheritance of immunity by offspring. We show how varying these factors and other model parameters, such as transmission rate of the disease, affect model predictions. We compare results for the case where both patches pose a risk of disease with the case where one patch is disease-free. The severity of undermatching is predicted to be much greater when only the higher quality patch is infected. This may have important implications for disease management.