Core Predictions of Island Biogeography Theory

MacArthur and Wilson’s model is built around two main factors: island size (area) and distance from the source pool (usually the mainland). The number of species on an island is determined by the balance between immigration and extinction rates, both of which are influenced by these factors.

1. Species-Area Relationship

• Prediction: The number of species on an island increases with its size or area.

• Explanation: Larger islands support more habitats, resources, and larger populations, leading to lower extinction rates and higher species richness1345678.

2. Species-Isolation Relationship

• Prediction: The number of species decreases as the distance from the source pool increases.

• Explanation: Islands that are farther from the mainland receive fewer immigrants, resulting in lower species richness13478.

3. Species Turnover

• Prediction: The composition of species on an island is dynamic, with continual immigration and extinction leading to frequent turnover.

• Explanation: Even though the total number of species may reach equilibrium, the actual species present can change over time23.

What the Theory Does NOT Predict

Species Richness and Distance to Neighboring Islands

• Statement: “Species richness on an island should be related to its average distance to the neighbouring islands.”

• Reality: The original MacArthur-Wilson model does not include the distance to neighboring islands as a factor in determining species richness. The theory focuses on the island’s area and its distance from the mainland source pool (not other islands), which acts as the primary reservoir of potential colonists134.

• While later models and studies have explored the role of island clusters, stepping stones, and metapopulation dynamics, these are not part of the core predictions of the original theory1.

Summary Table

Conclusion

The prediction that is NOT part of Wilson-MacArthur’s Theory of Island Biogeography is:

(4) Species richness on an island should be related to its average distance to the neighbouring islands.