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
Species
|
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
17.2.4.1 (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.
