How does island biogeography explain species distribution?

Island biogeography explains species distribution as a balance between immigration and extinction, influenced by island size and isolation.

Island biogeography is a study that attempts to understand the factors affecting the species diversity and distribution on islands. It is based on the equilibrium theory proposed by Robert MacArthur and Edward O. Wilson in the 1960s. According to this theory, the number of species on an island reflects a balance between the rate of new species immigration and the rate of species extinction.

The theory proposes two main factors that influence this balance: the size of the island and its isolation. Larger islands can support more species due to greater availability of resources and habitats. Therefore, the extinction rate on larger islands is lower than on smaller ones. On the other hand, the rate of immigration decreases with increasing isolation. Islands that are far from the mainland or other islands receive fewer new species because the chances of species successfully dispersing and colonising these islands are lower.

The equilibrium point, where the rate of immigration equals the rate of extinction, determines the number of species that an island can support. This is known as the island's carrying capacity. When the number of species exceeds this capacity, the extinction rate increases until equilibrium is reached again. Conversely, if the number of species falls below the carrying capacity, the immigration rate will increase until equilibrium is restored.

This theory has been used to explain the unique and diverse species distribution on islands. For example, islands that are close to the mainland and large in size, like the Galapagos Islands, have a high species diversity due to high immigration rates and low extinction rates. Conversely, small and isolated islands, like the Hawaiian Islands, have fewer species but a high proportion of endemic species (species found nowhere else in the world) due to low immigration rates and high extinction rates.

In conclusion, island biogeography provides a framework for understanding how species distribution is shaped by geographical factors and ecological processes. It highlights the dynamic and complex nature of biodiversity on islands, and the delicate balance between immigration and extinction.