An Introduction to Island Biodiversity
At its most basic, the definition of an island is a piece of land surrounded by water yet it actual ecological and geographical conditions that constitute a island are widely debated. For example some studies specify that islands must be populated or be located a certain distance from the mainland. Moreover, the composition and population of islands can vary widely depending on the nature of their formation, their location in relation to ocean currents or wind direction and whether they are inhabited.
Irrespective of these concerns, it is obvious from the studies of islands that they are home to a vast array of stunningly rare and diverse examples of life. Species that live on islands often are dispersed from elsewhere but are then confined to small isolated areas. This geographic seclusion from the rest of the species is a form of reproductive isolation that gives rise to speciation.
Speciation is an evolutionary process that results in the formation of a new species from a preexisting species. The island environment enacts evolutionary forces that result in the development of a gene pool distinct to that of the origin species. This occurs through cumulative mutation, genetic drift and natural selection. Allopatric speciation is a key reason why the flora and fauna of island ecosystems are so highly specialised and distinct. As a result of the high concentration of rich animal and plant life in a relatively small land area, islands are often referred to as biodiversity ‘hot spots’.
These subspecies are often endemic to the island they arose from and often display unusual characteristics that are particularly suited to island life. In Hawaii over 90% of the islands’ species are endemic to the region.
Examples of these adaptations include gigantism, dwarfism, flightlessness and loss of defence mechanisms. On the island of Palau in Micronesia, the jellyfish that reside in its saltwater cave systems lost their stinging defence mechanism over time due to a lack of predation.
"...islands are often referred to as biodiversity hot spots."