APES 2.3 Island Biodiversity

Enduring Understanding:

Ecosystems have structure and diversity that change over time.

Learning Objective:

Describe island biogeography.
Describe the role of island biogeography in evolution.

Essential Knowledge:

Island biogeography is the study of the 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.
Many island species have evolved to be specialists versus generalists because of the limited resources, such as food and territory, on most islands. The long term survival of specialists may be jeopardized if and when invasive species, typically generalists, are introduced and outcompete the specialists.

Two factors that influence the biodiversity are the size and distance of that habitat from a source of colonizing species. * These factors are the basis for island biodiversity.

Habitat size: * Larger habitats typically contain more species. * Dispersing species are more likely to find larger habitats than smaller habitats, particularly when those habitats are islands. * Larger habitats can support more species than smaller habitats. Larger habitats can support larger populations of a given species than smaller habitats. * Larger habitats often contain a wider range of environmental conditions, which in turn provide more niches that support a larger number of species than smaller habitats. * The wider range of environmental conditions also provides greater opportunities for speciation over time.
Distance: * The distance between a habitat and a source of colonizing species affects the species richness of various communities. * For example, oceanic islands that are closer to the mainland generally have more species than the islands located a greater distance away from the mainland. * Distance is relevant as only certain species can disperse long distances. Many species have the ability to disperse short distances.
Generalists vs. Specialists: * A generalist species is able to thrive and be successful in a wide variety of environmental conditions and can make use of a variety of different resources. * A specialist species can only thrive and be successful in a narrow range of environmental conditions and can only make use of limited resources, such as a limited diet. * Many island species have evolved to be specialists versus generalists because of the limited resources, such as food and territory, on most islands. * The long-term survival of specialists may be jeopardized if and when invasive species, typically generalists, are introduced and outcompete the specialists.
Alien vs. Native species: * Native species are species that live in their historical range, typically where they have lived for thousands to millions of years. * Alien species (“exotic” species) are species that live outside their historical range. * When alien species spread rapidly across large areas, we call them invasive species. * Rapid spread of invasive species is possible because invasive species do not readily have natural enemies in the regions where they are introduced.