Which statement is the best explanation of the model of island biogeography?
(a) As an island increases in species richness, the extinction rate decreases.
(b) As an island increases in species richness, the colonization rate increases.
(c) As an island increases in species richness, the extinction rate increases.
(d) As an island increases in species richness, the extinction rate and colonization rate both increase.
The Correct Answer and Explanation is:
The correct answer is (d) As an island increases in species richness, the extinction rate and colonization rate both increase.
Explanation:
The model of island biogeography, proposed by Robert MacArthur and Edward O. Wilson in 1967, explains the relationship between the size of an island and its distance from the mainland, and how these factors influence species richness (the number of different species present on the island). The model is based on the dynamic equilibrium between the rates of colonization (the arrival of new species) and extinction (the loss of species).
- Colonization Rate: This is the rate at which new species arrive on the island from nearby sources, typically the mainland or other islands. When a species-rich island is small or far from the mainland, it tends to have a lower colonization rate because it is more difficult for new species to reach the island. However, as the island accumulates more species, the colonization rate can increase. This happens because more species on the island provide more ecological niches and resources, which can attract even more species, leading to a positive feedback loop.
- Extinction Rate: As the number of species on an island increases, the extinction rate also tends to rise. This occurs because each additional species may compete for the same resources or space, leading to a higher likelihood of species being outcompeted or becoming extinct. Additionally, smaller populations of species are more vulnerable to environmental changes, disease, or other factors that can lead to extinction.
The equilibrium point occurs when the rates of colonization and extinction balance each other, resulting in a stable number of species. This equilibrium is influenced by the island’s size and its distance from the mainland. Larger islands or those closer to the mainland tend to have higher colonization rates and lower extinction rates, while smaller or more isolated islands have the opposite pattern.
Thus, as an island increases in species richness, both the extinction rate and the colonization rate increase, which is why answer (d) is the best explanation of the model of island biogeography.