Britannica Sources used in this answer

Why do remote oceanic islands often have fewer species than nearby mainland areas?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing energy flow in a food chain from a tree to a caterpillar, then to a bird, and finally to microbes, with red arrows illustrating energy transfer and heat loss at each stage. — community ecology Energy transfer and heat loss along a food chain.

In the context of community ecology, remote oceanic islands typically support fewer species than mainland areas due to several key factors related to colonization and geography:

Barriers to Dispersal: The primary reason for lower species richness is the distance or physical barrier separating an island from potential source populations. The probability of species successfully reaching remote islands is slight, particularly for animals that lack the ability to fly or travel long distances across water.12
Colonization and Time: Islands often have fewer species because they are difficult to reach or, in some cases, are of relatively recent geological origin, meaning there has not been sufficient time for organisms to arrive and establish stable populations.13
Island Size: According to the theory of island biogeography, the number of species on an island is proportional to its size and inversely proportional to its distance from the mainland. Smaller islands generally offer fewer habitats, which limits the variety of species that can be supported.13

While these factors lead to lower species richness, it is important to note that the species that do successfully colonize islands often experience reduced competition, which can lead to higher relative abundance for those specific populations compared to their mainland counterparts.14