Question

How does proximity to the mainland affect the immigration rate on the island? Why? How does dispersal ability effect which species are able to get to an island?

Answer 1

Immigration is higher on near islands than on distant islands (in relation to the mainland), hence the equilibrium number of species present will be greater on near islands. Everything else being same, close islands will have high immigration rates and support more species with respect to distant islands.

The "mainland" is the source of new immigrants to the island. Taking in account all new species immigrate to the island from the mainland, closer islands will have more species on them than far islands, just because closer islands are easier to reach. Also, there is more of a chance that new immigrants will arrive and keep a species in existence on that island resulting in lesser extinction rate.

Organisms with high dispersal capabilities, such as plants(air, wind, water pollinated) and birds, are much more common on islands than are poorly dispersing classes like reptiles and mammals. However, some mammals are present on islands, presumably from swimming or riding on natural rafts, that are washed out from the mainland. Species to get in islands are also influenced by dispersal distance, seed mass, species longevity and by the number of islands occupied by the species.