Question

Which of the following statements about the equilibrium theory of island biogeography is FALSE?

Answer 1

Answer:

b) At equilibrium, the species composition of an island will not change.

Explanation:

The Theory of Island Biogeography written by Robert H. MacArthur and Edward O. Wilson (1967) is an essential book for any professional working in biogeography, biodiversity, ecology, conservation and related fields. The theory of island biogeography states that species diversity on islands tends to approach a dynamic equilibrium due to the balance between colonization (inmigration), speciation and extinction. At equilibrium, the species composition of an island will change, precisely at the time that immigration and extinction processes maintain the number of species in a dynamic equilibrium, thereby maintaining species diversity. In this case, the colonization rate represents a function of distance to the continent (or other islands), the extinction rate is a function of the size of the island and habitat heterogeneity, and speciation is a function of time. This book also contains a series of useful considerations: 1-the number of species in an area is directly associated with the size of the area; 2-large islands support more diverse communities than small islands; 3-the viability of populations on island systems can be considered as a function of the island size and its proximity to the mainland (or other islands); and 4- when a habitat is lost the remaining fragmented area may lose some of its important species.

Answer 2

Answer:

b) At equilibrium, the species composition of an island will not change

Explanation:

According to MacArthur-Wilson (1967) equilibrium theory of island biogeography

• 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.

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 a continuous species renewal.
• If the island gets bigger, species richness increases.
• If the island is closer to the mainland, species richness increases.

The model has been criticized for its predictions and assumptions. What actually happens in nature might differ from the assumptions.

• Target effect: The immigration rate not only depends on the distance of the island to the continent but also on the size of the island. Bigger islands are easier to see than smaller islands.
• Rescue effect: The Extinction rate not only depends on the size of the island but also the distance. Closer islands have higher chances of being colonized than the farther ones.
• Not all species have the same chances of getting to the islands because species vary in their dispersion capabilities. The theory does not consider in situ evolution.

However, despite the critics, the theory has significant contributions:

• It is a simple model that helps to define and interpret predictive models.
• It considers competition and competitive exclusion → As the number of species increases, the extinction rate increases too.
• It applies to different habitats such as patches, corridors, natural reserves, among other island-like areas.
• Useful for interaction and trophic webs conservation