Question

Adaptive radiations on archipelagos (island chains) represent some of the best-understood speciation events. Why is an ancestral species more likely to give rise to multiple descendent species on an archipelago than on an equal-sized area of mainland?

Hint: Regions that are highly subdivided by geographic barriers such as archipelagos typically have more species than do regions with fewer barriers. The barriers lead to reproductive isolation between populations, initiating allopatric speciation.

a. By chance, different species will colonize different islands in a chain.
b. Favorable mutations are more likely to arise on an archipelago as populations try to adapt to conditions on their specific island.
c. Populations on nearby islands are more likely to be genetically isolated than populations that are equally close to one another on the mainland.

Answer 1

An ancestral species is more likely to speciate on an archipelago due to geographical isolation, allowing adaptive radiation to occur with less interbreeding than on comparable mainland areas.

Step-by-step explanation:

An ancestral species is more likely to give rise to multiple descendant species on an archipelago than on an equal-sized area of mainland because of geographical isolation. Islands, being separated by water, create isolated habitats which prevent gene flow between populations of the same species. This isolation allows for adaptive radiation, a process in which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches. For example, the Hawaiian honeycreeper species illustrate adaptive radiation, evolving from one founder species into many diverse forms.

Contrastingly, on the mainland, populations tend to be less isolated and thus, more likely to interbreed, which can reduce the chances of speciation. Island biogeography, a concept developed by MacArthur and Wilson, further explains that factors such as migration, speciation, and extinction are influenced by the isolation of island populations, leading to a unique and rich biodiversity.