Working Group II: Impacts, Adaptation and Vulnerability

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17.2.5. Biodiversity of Islands

Small islands are highly variable with respect to their biological diversity. Some states, such as the low reef islands, have low biodiversity and low endemism. Coral reefs exhibit the highest known diversity among marine ecosystems, with 91,000 described species of reef taxa. Table 17-4 gives the diversity of mammals, birds, plants, and endemism for some select small island states. In general, small islands in absolute figures tend to have high terrestrial diversity and endemism. In Cuba, for instance, 50% of the flora and 41% of the fauna are endemic (Vales et al., 1998). In the Canary Islands, 45% of all bird species are endemic. In the Hawaiian islands—the most isolated of all floristic regions—more than 90% of plant species are endemic (Biagini, 1999). When relative biodiversity and endemism are calculated in relation to area, the figures for many small island states tend to be higher than those for most other regions of the world.

Table 17-4: Biodiversity status for selected small island states, 1990 (extracted from IPCC, 1998).

Country Known Mammal Species Known Endemic Mammal
Known Bird Species Known Endemic Bird Species Known Plant Species Known Endemic Plant Species
Cuba 31 12 342 22 6,004 3,229
Dominican Republic 20 - 254 0 5,000 1,800
Fiji 4 1 109 26 1,307 760
Haiti 3 0 220 0 4,685 1,623
Jamaica 24 3 262 25 2,746 923
Mauritius 4 2 81 9 700 325
Palau 214 57 708 80 10,000 -
Solomon Islands 53 19 223 44 2,780 30
Trinidad and Tobago 100 1 433 1 1,982 236

Although there generally is high diversity associated with the ecosystems (marine and terrestrial) of islands, their long-term survival is threatened by anthropogenic stresses including pollution, overexploitation, and generally poor management. As in other regions, it is expected that climate change will affect the biodiversity of small islands directly and indirectly. Rising atmospheric CO2 concentrations are projected to increase the productivity of some communities and alter competition among others by eliminating some species and introducing new species to take their place (McIver, 1998). In marine ecosystems such as coral reefs, incremental increases in atmospheric CO2 would be expected to threaten the diversity of these systems by the process described in Section (Hatcher, 1997).

The impacts of climate change and sea-level rise on biota in island states are much greater than the impacts on continental areas. For example, sea-level rise could impact the habitats of the endangered Tuamotu sandpiper (Prosobonia cancellata) and bristle-thighed curlew (Numenius tahitiensis), as well as the seabird colony of 18 species on Laysan Island (Hawaii). Other potentially vulnerable areas (not inclusive) for breeding seabirds include the Kerguelen and Crozet Islands (seabirds), the Galapagos Islands (Galapagos penguin, Spheniscus mendiculus), and the nesting habitat for the Bermuda petrel (Pterodroma cahow) (Sattersfield et al., 1998). Based on outputs from HADCM2 and scenarios IS92a and Kyoto 1, Suarez et al. (1999) also have found that in the eastern region of Cuba, certain endemic species of flora would face extinction.

Inundation and flooding of low-lying forested islets with species such as the Manus fantail (Rhipidura semirubra) also might be lost. The majority of threatened bird species on islands are found in forested habitats (Sattersfield et al., 1998). Impacts of climate change on these species likely would be from physiological stress and changes and loss in habitat, especially from fires and cyclones. For example, 30% of the forested area on the Santa Cruz islands was lost in one cyclone in 1993. Some vulnerable species and areas include the endangered New Caledonian lorikeet (Charmosyna diadema) and critically endangered New Caledonian rail (Gallirallus lafresnayanus) on New Caledonia, the Samoan white-eye (Zosterops samoensis) and critically endangered Samoan moorhen (Gallinula pacifica) on Savai'i (Samoa), and the Santo Mountain starling (Aplonis santovestris) on Espiritu Santo (Sattersfield et al., 1998). In Samoa, most species of flowering plants are pollinated by a few species of animals; nearly 100% of seed dispersal in the dry season is mediated by flying foxes (Pteropus spp.) (Cox et al., 1991). Likewise, flying foxes are the key pollinators and seed dispersers on many islands in the South Pacific. If their habitat is threatened by climate change, the result would be the loss of many dependent plant species.

Generally on islands, one of every three known threatened plants is endemic. Among birds, approximately 23% of the species found on islands are threatened, compared with only 11% of the global bird population (McNeely et al., 1993). Establishment of terrestrial, marine, or coastal reserves such as the Morne Trois Pitons Park and Forestry Reserve (Dominica, 1986), Bonaire Marine Park (Netherlands Antilles, 1979), Tobago Cays Marine Park (St. Vincent and the Grenadines), Soufriere Marine Management Area (St. Lucia, 1997), and other similar management units ("biosphere reserves") established elsewhere is a useful management option. It has been demonstrated that the creation of such reserves helps to preserve endangered habitats and ecosystems of small islands and will contribute to maintenance of biological diversity, while increasing the resilience of these systems to cope with climate change.

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