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Island Biodiversity - What's the Problem?

The unique characteristics that make island biodiversity so special also leave it particularly fragile and vulnerable. Despite the high levels of biodiversity and the prevalence of endemism, island species are present in relatively small numbers, making them very vulnerable to extinction. Furthermore, because island species have diminished dispersal capability and evolve in competition with relatively few other species, they develop survival strategies based on interdependency, co-evolution, and mutualism rather than defence mechanisms against a broad range of predators and competitors. As a result, many island species have become rare or threatened, and islands have a disproportionate number of recorded species extinctions when compared to continental systems. Of the 724 recorded animal extinctions in the last 400 years, about half were of island species. At least 90% of the bird species that have become extinct in that period were island-dwellers.

Biodiversity loss is a particular concern on islands. The Report of the Global Conference on the Sustainable Development of Small Island Developing States (also known as The Barbados Programme of Action for the Sustainable Development of Small Island Developing States, BPoA, referred to the biological diversity of island ecosystems as “among the most threatened in the world”, due to their small size, isolation and fragility (Bridgetown, Barbados, 25 April-6 May 1994, Annex II, preamble, paragraph 6). More recently, the Millennium Ecosystem Assessment concluded that the main drivers of island biodiversity loss would either continue or increase rapidly. It projected that the impacts of climate change and pollution from nutrient loading will become increasingly severe and that the impacts associated with habitat change, over-exploitation and, particularly, invasive species will continue to be high or, in the latter case, very high.

This pressure is keenly felt by island economies. Among the most vulnerable of the developing countries, small island developing States (SIDS) depend on the conservation and sustainable use of island biodiversity for their sustainable development.

Over the past century, island biodiversity has been subject to intense pressure from:

The most significant impacts of climate change are sea-level and sea-surface temperature rise. Because most small islands are low lying and have a large exposure of coasts in relation to landmass, as well as a high concentration of population in coastal zones, islands are extremely vulnerable to sea-level rise. Experts predict that average sea level could rise by as much as 21 centimetres by 2025 and 66 centimetres by 2100, leading to inundation, storm surge or shoreline erosion with the potential to destroy island economies. Sea-level rise will also cause increased salinity due to encroachment of the sea and saltwater intrusion into freshwater lenses, contributing to an increasing shortage of the water supply and loss of agricultural land.

Scientists predict that by the end of the 21st century, the Earth’s mean surface temperature will warm 1.4 to 5.8°C. The rise in sea temperature causes coral bleaching, which negatively affects fishes, sponges, giant clams, mollusks and other sea creatures, whose survival depends on reefs. As a result, the food security and economies of islands, which are largely dependent on marine ecosystems, will be negatively affected.

  • United Nations
  • United Nations Environment Programme