Rescue effect

The rescue effect is a phenomenon which was first described by Brown and Kodric-Brown, and is commonly used in metapopulation dynamics and many other disciplines in ecology. This populational process explains how the migration of individuals can increase the persistence of small isolated populations by helping to stabilize a metapopulation, thus reducing the chances of extinction. In other words, immigration can lead to the recolonization of previously extinct patches, promoting the long-term persistence of the network of populations. The rescue effect is remarkably important in areas where the persistence of a species is threatened because of the increasing rates of habitat destruction and fragmentation. If the distributional extent of a species is reduced because of its habitat destruction, the migration rate will decrease producing a decline in the abundance of another population (of the same species) whose patch has been unaltered. This is a clear example, of how the reduction or elimination of interpatch movement and consequently the lack of the rescue effect, is directly related with the abundance and patch occupancy of a species. The same consequences on the abundance and distribution can be observed when different landscapes or patches are unconnected because of the lack of wildlife corridors. Also the opposite situation can be observed when the rate of immigration per patch increases as the proportion of patches that are occupied increases, resulting in a positive relation between local abundance and the number of occupied patches. Consequently, metapopulation dynamics and landscape connectivity for the persistence of populations in fragmented landscapes are important factors to take into account when managing endangered species. The rescue effect is a common influence on many island populations, even if it seems not obvious due to their apparent lack of connection with the mainland.