On the impact of migratory flows on the residential species of a region

Migrations can trigger biological invasions. Indeed, when a migrant population finds favorable conditions in a region, it can settle there permanently. This can pose a threat to local biodiversity. Moreover, even when a biological invasion does not occur, a migratory transit affecting a territory can harm residential species. In this paper, we focus on a migrant population that either only touches the border of the region occupied by residents or crosses it altogether. We investigate the possible negative consequences due to a migratory flow for a native species that interacts with the migrants in some particular scenarios. Specifically, we consider the following situations: migratory interference with negative or positive effects on the native species, migrant predation on the residential population, competition and symbiosis of the two populations. By analytically and numerically exploring the mathematical models for the migrant-resident interactions of interest, we find that in the interference scenarios migrant biological invasions cannot occur, while in the others they do. The only migrant disturbance action, however, could still have serious consequences for the native population, which may even be driven to extinction. We can also have the resident extinction in the models of migrant predation on residents and competition. In the positive interference and symbiosis scenarios, instead, the system can only evolve toward coexistence. The residents, in these last two situations, benefit from the migratory transit. These general results are valid for both marginal and non-marginal migrant-resident contacts, but we also observe some differences in these two cases.