Islands such as Madagascar, Galapagos, New Zealand, the Hawaiian Archipelago, and Australia, have a large population of widespread and specialized flora and fauna. Islands are geographically isolated, a factor that hinders migration of species from the mainland into the islands.
This enables conventional organisms in the isle to grow without being attacked by predators and competitors. Invasive exotic species introduced by humans can have a serious effect on isolated ecosystems such as islands; in fact, these exotic species are among the main factors that have led to extinction of some native species in these islands (Smith & Smith, 2009).
The main reason exotic species normally pose a greater threat to native species in the island is because island species might have evolved in the absence of strong predators and competitors. This makes native species in an island lack the necessary mechanisms they need to survive due to the presence of exotic species introduced by human activities.
Native species also fail to inhabit certain places to avoid being disturbed by populations, which colonize the area. This increases the likelihood of exotic species succeeding in the event they invade the island. Human activity has introduced exotic species that if left on their own, would not have managed to immigrate to islands.
These exotic species do not resemble native species, and are a threat to them due to their unpredictable negative effects. Some of the exotic species that have been known to have the greatest negative consequences on the native island species are mammalian herbivores, feral cats, and rats (Smith & Smith, 2009).
Exotic animals and plants introduced by humans are a threat to native species in an island because in most cases they do not align themselves to the island’s biogeographical factors. Invasive exotic species have unpredictable effects that destabilize the biogeography of the island (Huggett, 2009).
For example, foreign organisms are invading Hawaiian habitats 2 million times faster than would be considered appropriate. This has hugely distorted the island’s environment and led to the extinction of vulnerable organisms.
Research has shown that the size of an island is also a contributing factor in extinction in the event exotic species are introduced in an island. Native species in a small island are at high risk when exotic species are introduced (Langor & Sweeney, 2009).).
Studies have indicated that disease causing microorganisms, plants and animal cause a specific threat to island birds, and have played a significant role in the extinction of certain birds. For example, over 50% Hawaiian wild birds have died out due to invasion by predators, infection causing microbes and the loss of natural habitats. Alien vegetation, grass, and flowers could also make the island’s biodiversity richer.
However, due to lack of adaptive mechanisms by native plants, the exotic species take over the island, and either kill or over crowd native species. When the introduced, exotic plants kill native ones and as a result, extinction of some native plant species may occur.
The extinct native plants may never be found anywhere else in the planet, and this not only reduces the biodiversity of islands, but also that of the entire planet (Smith & Smith, 2009).
Exotic species are a greater threat to the existence of native species for isolated habitats such as islands than they are for larger patches of habitats because species in islands evolve in the absence of strong predators and competitors.
When exotic species from the main land are introduced in the island, native species normally lack the ability to compete with the former, a factor that might lead to the extinction of the latter (Smith & Smith, 2009).
References
Huggett, R. (2009). Physical geography: The key concepts. Madison Avenue, NY: Taylor & Francis.
Langor, D. W., & Sweeney, J. (2009). Ecological Impacts of Non-Native Invertebrates and Fungi on Terrestrial Ecosystems. Edmonton, AB: Springer.
Smith, T. M & Smith, R. L. (2009). Elements of ecology. Toronto: Pearson Benjamin Cummings.