Island biogeography

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Island biogeography

The distribution of plants and animals on islands. Islands harbor the greatest number of endemic species. The relative isolation of many islands has allowed populations to evolve in the absence of competitors and predators, leading to the evolution of unique species that can differ dramatically from their mainland ancestors.

Plant species produce seeds, spores, and fruits that are carried by wind or water currents, or by the feet, feathers, and digestive tracts of birds and other animals. The dispersal of animal species is more improbable, but animals can also be carried long distances by wind and water currents, or rafted on vegetation and oceanic debris. Long-distance dispersal acts as a selective filter that determines the initial composition of an island community. Many species of continental origin may never reach islands unless humans accidentally or deliberately introduce them. Consequently, although islands harbor the greatest number of unique species, the density of species on islands (number of species per area) is typically lower than the density of species in mainland areas of comparable habitat. See Population dispersal

Once a species reaches an island and establishes a viable population, it may undergo evolutionary change because of genetic drift, climatic differences between the mainland and the island, or the absence of predators and competitors from the mainland. Consequently, body size, coloration, and morphology of island species often evolve rapidly, producing forms unlike any related species elsewhere. Examples include the giant land tortoises of the Galápagos, and the Komodo dragon, a species of monitor lizard from Indonesia. See Polymorphism (genetics), Population genetics, Squamata

If enough morphological change occurs, the island population becomes reproductively isolated from its mainland ancestor, and it is recognized as a unique species. Because long-distance dispersal is relatively infrequent, repeated speciation may occur as populations of the same species successively colonize an island and differentiate. The most celebrated example is Darwin's finches, a group of related species that inhabit the Galápagos Islands and were derived from South American ancestors. The island species have evolved different body and bill sizes, and in some cases occupy unique ecological niches that are normally filled by mainland bird species. The morphology of these finches was first studied by Charles Darwin and constituted important evidence for his theory of natural selection. See Animal evolution, Speciation

Island biogeography theory has been extended to describe the persistence of single-species metapopulations. A metapopulation is a set of connected local populations in a fragmented landscape that does not include a persistent source pool region. Instead, the fragments themselves serve as stepping stones for local colonization and extinction. The most successful application of the metapopulation model has been to spotted owl populations of old-growth forest fragments in the northwestern United States. See Biogeography, Ecological communities, Ecosystem

References in periodicals archive ?
After World War II, she studied biology at Aberystwyth University, gaining a 1st class honours in botany and followed that with a PhD in island ecology - a topic which she remained an expert in for the rest of her life with international acclaim and recognition.
There are concerns that this will lead to a further loss of sea ice and increase land temperatures, resulting in a changing island ecology and contributing to further global warming, as dark, ice-free land warms much more quickly because it retains, rather than reflects, the sun's heat
Ritual releasing of wild animals threatens island ecology.
Authors of these 8 chapters have focused on such topics as island ecology and speciation, the role of pollination and herbivory on plant evolution, ecological and phylogenetic constrains on adaptive radiation, how insect diversification may lead to diversification of natural enemies, and how diversification in plants (for example, figs) can give rise to diversification in insects and their associated parasitoids.
Aquarium's (MEC & A) Gear-up Mississippi Island Ecology Camp
Ultimately, the island ecology is being adversely altered by negligence.