Island Biogeography Calculator

The MacArthur-Wilson theory explains species richness on islands as a dynamic equilibrium between colonization from mainland sources and local extinction. It predicts that larger islands closer to the mainland will have more species.

At equilibrium, the rate of new species arriving (colonization) equals the rate of species going extinct. The balance between these rates determines the final number of species that can coexist on an island.

Larger islands can support larger populations, which are less likely to go extinct due to random events. They also offer more diverse habitats and ecological niches, allowing more species to coexist.

Islands farther from the mainland receive fewer colonizing species because organisms have greater difficulty crossing larger distances. This results in lower colonization rates and ultimately fewer species.

The species-area relationship describes how species richness increases with habitat area, typically following a power law. The relationship is often expressed as S = cA^z, where z is usually between 0.2-0.35.

Extinction rates are influenced by island area (smaller islands have higher extinction), population sizes, habitat diversity, and environmental variability. Smaller populations on smaller islands are more vulnerable to extinction.

The model helps predict how habitat fragmentation affects biodiversity and guides reserve design. It suggests that larger, less isolated protected areas will maintain more species over time.

Species turnover is the rate at which species composition changes over time through colonization and extinction events. Even at equilibrium, individual species may come and go while total richness remains constant.