Practice question

The rescue effect occurs when immigrants enter a small, declining local population and reduce its probability of extinction. New arrivals add individuals directly, can increase reproduction by supplying mates, and may restore genetic variation or reduce inbreeding. The patch remains occupied throughout; immigration “rescues” it before abundance reaches zero. This differs from recolonization, which establishes a population in a patch after local extinction has already occurred. In metapopulation models, both processes depend on connectivity, but they affect occupancy in different ways: rescue lowers the local extinction rate, whereas recolonization raises the colonization rate of empty patches. Predator control and resource reallocation are management actions, not the defining mechanism. Increased reproduction may contribute after immigrants arrive, but immigration is the causal link between patches. Very high connectivity can also synchronize populations or spread disease, so more dispersal is not always beneficial. The rescue effect is strongest when donor populations provide migrants and the recipient patch remains suitable enough for those migrants to survive and reproduce.