Migration is a strategy often used to avoid infection by pathogens or parasites in a wide range of taxa. Previous work has identified three different processes contributing to reduced cost of pathogens/parasites via migration: migratory escape, culling of infected individuals during migration, and migratory recovery, where individuals lose their parasites and recover during the journey. However, most theory to date assumes that individuals that have a single strategy during both infected and susceptible states, meaning an individual’s status (susceptible or infected) is irrelevant to its decision to migrate. We derive a model by defining two independent strategies of migration for an individual based on whether they are infected or susceptible to study how it impacts the population’s migration strategy.
Results/Conclusions
When migration provides only a single benefit (escape or recovery), we show that either no migration or complete migration of the population of an infected state are the only two outcomes that arise. There is no instance of partial migration arising in this model within an infected state. Analysis of the model integrating both processes (escape and recovery) reveals that partial migration at the level of the population arises which agrees with the earlier results which showed scenarios where partial migration emerged as the optimal strategy for movement. We show here that when an individual has different migration strategies for different infection states there does not arise a case where partial migration is an optimal strategy within the individuals of an infected state. Hence, we have parsed out the contributors to partial or complete migration by determining which individuals in the population are involved in migration for different sets of conditions.