The theory of island biogeography explains that two factors affect island colonization. These are migration and extinction, associated with the distance from the mainland and the island size. Option D. Migration rates.
What is the theory of island biogeography?
The ecologists MacArthur and Wilson took the term island biogeography to refer to the predictions about the number of species inhabiting an island.
According to MacArthur-Wilson (1967)
- The number of species on an island represents a dynamic equilibrium between the opposite forces of immigration and extinction rates.
- At equilibrium, the species richness keeps constant. But the species composition changes.
- Each island can have a certain number of species, but these species are not always the same, meaning that species might renew. Interspecific competition has a significant role.
Island biogeography theory establishes that the two factors that affect species richness in natural communities on an island are the distance from the mainland and the size of the island.
At the same time, these factors affect immigration and extinction rates.
According to the theory,
- Effect of distance ⇒ islands that are closer to the continent have higher possibilities of receiving immigrants than those islands that are located farther from the mainland.
- Effect of size ⇒ relation between island size and species diversity. On smaller islands, the probability of extinction is higher than on bigger islands. Bigger islands can have more species than smaller ones.
The assumptions of the equilibrium theory:
- The immigration rate depends on the distance of the island to the mainland.
- The extinction rate depends on the island size.
- All the species have the same chances of getting to the island.
Predictions:
- At equilibrium, the number of species is constant in time.
- Dynamic equilibrium means continuous species renewal.
- If the island gets bigger, species richness increases.
- If the island is closer to the mainland, species richness increases.
The correct option is Migration rates. Option D.
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