⏳ Estimated Reading Time: 5 - 7 minutes

Describe island biogeography and its role in evolution.

What is Island Biogeography?

Island biogeography is the study of how islands affect the diversity and evolution of species. It is based on the theory developed by Robert MacArthur and E.O. Wilson in the 1960s which states that the number of species on an island depends on two factors: the size of the island and the distance from the mainland.

According to the theory, larger islands have more species richness because they have more ecosystem diversity, more niches, and larger population sizes.

a large island labeled 1 and a small island labeled 2. Many arrows are coming from one spot on the mainland — A large island (1) and a small island (2) are both about the same distance from the mainland. Because the Island 1 is larger, it is more likely to receive species from the mainland because organisms coming from the mainland are more likely to find the Island 1 due to its size.

Islands closer to the mainland have more species richness because they have more colonizers and more genetic diversity.

Two islands of approximately the same size, labeled A and B. A is farther from the mainland, while B is closer. — ***Islands A and B are both approximately the same size, but Island B is closer to the mainland, so it is easier for organisms from the mainland to make the voyage to the island.***

Therefore, according to the theory, the highest species richness will be found on large islands close to the mainland and the lowest species richness will be found on small islands far from the mainland.

Explore the islands on the graph below to learn more about how each island's size and proximity to the mainland has shaped the flora and fauna on the island, Just tap on the white dots at the bottom to uncover all the details!

Essential Knowledge

Island biogeography is the study of ecological relationships and distribution of organisms on islands and of these organisms' community structures.

Islands have been colonized in the past by new species arriving from elsewhere.

Most Island Species are Specialists

Island biogeography shapes evolution by creating isolated environments that expose species to different selective pressures and opportunities.

Explore the presentation below to learn more about how biogeography can shape evolution:

Because islands are so much smaller than the mainland, species on islands are more likely to specialize so they can fill every available niche on the island and reduce competition for the limited resources on the island.

Essential Knowledge

Many island species have evolved to be specialists versus generalists because of limited resources, such as food and territory on most islands.

The Role of Invasive Species on Islands

dodo bird drawing — ***The dodo bird was an example of a flightless bird endemic to an island called Mauritius.***

Islands, due to their isolation, often have specialized species that are adapted to their specific environment - climate, plants, predators, and prey native to the island.

For example, many islands have flightless birds because the birds have lost the ability to fly because this trait was no longer beneficial to the population as a way to escape predators. The dodo bird was an example of a flightless bird endemic to an island called Mauritius. Once humans arrived in Mauritius, invasive species, such as rats, pigs, and monkeys. These invasive species destroyed the dodo's habitat and the rats and pigs preyed on dodo eggs. With the loss of habitat, disruption to their reproductive cycle, and humans hunting the birds for meat, the dodo population quickly declined.

Invasive species are frequently generalists, which means they can survive and be successful in a variety of ecosystems, not just their native ecosystem. When these generalist species arrive on an island, their broad tolerances enable them to out-compete the native specialists.

Essential Knowledge

The long-term survival of specialists may be jeopardized if and when invasive species, typically generalists are introduced and outcompete the specialists.

[CC BY-NC-SA 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION - INTENDED ONLY FOR USE WITHIN LESSON.