Island Biogeography (College Board AP® Environmental Science): Study Guide

Ecology of island species

• Island biogeography is the study of:

  • The distribution of island species and ecosystems in geographic space and through time (biogeography)

  • The relationships between island species and their environment (ecology)

  • Community structures on islands

• Islands are often unique environments

• They often have distinct ecological dynamics due to their isolation

  • For example, islands often have fewer predators, resulting in unique adaptations among species

• The size of the island and its distance from the mainland influence biodiversity

  • Larger islands support more species

    • This is due to greater habitat diversity

  • Islands closer to the mainland are more likely to receive new species

    • This occurs via the process of colonization

Colonization of islands by new species

• Islands have been colonized over time by new species arriving from other locations

  • Arrival methods include:

    • Floating on debris

    • Flying

    • Carried by the wind

    • Carried by ocean currents

    • Hitchhiking on larger animals

    • Brought by humans, e.g. on ships (intentionally or unintentionally)

  • For example, coconut palms spread to islands by floating on ocean currents

• Colonizing species often adapt to the unique conditions of islands, such as limited food sources, varying climates, or the absence of predators

  • These adaptations allow them to exploit specific resources or roles within the ecosystem

  • This leads to the formation of new ecological niches

  • For example, a bird species arriving on an island might adapt to feed exclusively on a particular plant or insect that is abundant in its new environment

• Colonization rates depend on:

  • The island’s proximity to a source of species (e.g. proximity to the mainland)

  • The availability of suitable habitat

Evolution of island species

• Island biogeography plays a significant role in the evolution of species

  • Many island species evolve into specialists due to limited resources like food, space, and mates

  • Specialists are highly adapted to specific ecological roles

  • This makes them vulnerable to environmental changes and competition

• Invasive species, often generalists, pose a threat to specialists by outcompeting them for resources

  • For example, the introduction of rats to certain islands has devastated populations of ground-nesting birds, which are specialists with no defenses against such predators

Island evolution and specialism

• Galápagos finches:

  • The Galápagos Islands are home to finches that have evolved different beak shapes and sizes to exploit various food sources, such as seeds and insects

  • These adaptations are evidence of how isolation and resource availability drive evolutionary divergence

• Hawaiian honeycreepers:

  • Hawaiian honeycreepers are a group of more than 50 bird species found in the Hawaiian archipelago
    Over time, these birds developed specialized beaks to feed on nectar, insects, or fruit

  • The differences that have arisen between the new species often enable them to live together in one habitat because they are able to fill different ecological niches