A guide for planners and managers - IUCN

212 MARINE AND COASTAL
PROTECTED AREAS
Photo by R. Salm.
ecosystems. There are exceptions to all of these usual characteristics in some islands,
but together these characteristics define the major differences underlying insular and
continental habitats. The biological characteristics result directly or indirectly from
the operation of geographical, climatic, and geological features over time. Similarly,
an island’s historical and economic characteristics result from the operation of all the
previous characteristics, among which remoteness, small size, and impoverished
biotic variety are probably the most important.
The native terrestrial floras and faunas of oceanic islands have fewer forms
compared to those of similar areas on continents. However, older oceanic islands may
have large numbers of unique or endemic species of singular scientific interest that
are undergoing evolutionary radiation. An important consequence of the “impoverished”
biota of oceanic islands is that their food chains tend to be shorter than those of
continents or continental islands. Lack of native mammalian herbivores (and probably
few herbivores generally and an impoverished range of decomposers) and lack of
mammalian carnivores render the native biota of ocean islands particularly vulnerable
to such animals when they are introduced by people. Many endemic plants on oceanic
islands display primitive features of leaf anatomy and are particularly palatable to
such herbivores as goats.
The terrestrial flora and fauna of oceanic islands may have high turnover
(colonization and extinction) rates, even under natural conditions. This is particularly
true of small islands independently of direct or indirect human effects. MacArthur
and Wilson (1963) affirm on both theoretical and empirical grounds that the turnover
rate of species varies inversely with island area. Oceanic islands frequently support
enormous populations of marine birds, mammals, and reptiles that feed at sea but
rest and reproduce ashore (Figure II-28 and 29). Such congregations of marine
creatures have direct effects on insular ecosystems during certain seasons because
of their import of plant nutrients and
FIGURE II-28.
their disturbance of plant growth in
turning over the soil (notably
burrowing seabirds).
A red-footed booby chick (Sula sula) in the branches of a
Rhizophora mangrove, Aldabra Atoll strict nature preserve and
World Heritage Site.
Diamond (1976) demonstrated
that the boundary shapes and dispositions
of nearby reserves in relation to
one another, as well as their sizes,
are important in minimizing extinction
rates of birds. Temple (1981)
advocated the transfer of some
endemic species of land birds from
one island to another in the Mascarene
Islands because they were
supposedly endangered by competition
with other native species from