Origin of the theory
MacArthur
and Wilson (1967) made their original observations in the Pacific
archipelagoes. They noted that large islands had more species than small
islands and that islands near to the mainland had more species than others
further away.
They related patterns of distribution to rates of colonisation
and extinction. This means that the number of species found on an island
represents a balance between the rate of colonisation and the rate of
extinction.
Islands near a mainland have greater colonisation rates
than those further away. This is because the mainland provides a species
source. That is, a larger area from which species can disperse.
Extinction is higher on smaller islands because the
population size is smaller.
This theory was important in ecology because it described
patterns of species distributions on islands quite well (Forman,
1995).
