Host movement plays an important role in disease ecology for migratory wildlife. Migration can spread parasites to new areas, but may also improve overall population health via escape from infection hotspots or via the culling of heavily infested individuals from the herd.
In the Arctic, many species undergo seasonal migrations to follow changes in food availability, shelter, or mating opportunities. Climate change is facilitating the spread of parasites in the Arctic by altering development and mortality rates of parasites. The combined effect of host movement and climate-induced changes to parasite dynamics on the health of wildlife is unclear, and likely context dependent.
Mathematical models are powerful tools for understanding the interactions among biological processes, such as parasitism and migration, in light of environmental change. We developed a spatially explicit modelling framework for of the macroparasite dynamics of migratory host populations, and considered temperature-dependent rates of parasite development and mortality according to the Metabolic Theory of Ecology (MTE). As a case study, we apply our model to migratory caribou and their helminth parasites, using experimental data on temperature-dependent development and mortality in helminths to inform model parameters.
Results/Conclusions
The model we developed is the first to consider spatially explicit changes in parasite burdens of migratory hosts, and associated impacts on host migratory ability and survival. General model simulations revealed a previously undescribed phenomenon we term parasite-induced migratory stalling, whereby a positive feedback between infestation and slowing migration at infection hotspots, such as stopover sites, resulted in heavily infested hosts halting their migration.
Focusing on migratory caribou as a case study, incorporating temperature-dependent development and mortality of helminth parasites provided insight into how parasite dynamics may change with global warming. Caribou are thought to rely on migratory escape after breeding to reduce environmental transmission of certain parasites. Preliminary results suggest that warming temperatures lead to a decrease in generation time for parasites that may allow for reinfection of hosts at the breeding grounds before migratory escape is possible. Such a shift could have devastating consequences for caribou host populations, particularly if it leads to parasite-induced migratory stalling at breeding grounds.
The model we developed provides a general theoretical framework to explore host-macroparasite dynamics for migratory species in the face of environmental change. Such mechanistic models are needed in order to predict, preparing form and mitigate the potential impacts of climate change on ecosystems and people.