due to habitat alteration and the interactions of sev-
eral introduced organisms. The exotic birds and
mosquitoes act as vectors, and the exotic disease
provides the proximal cause of mortality. The fact
that introduced birds act as vectors illustrates that
important interactions between organisms at the
same trophic level are not all obviously ‘competi-
tive’ in nature.
Habitat degradation and loss
Probably the most renowned example of insular
habitat degradation is the case of Easter Island, a
depressing experiment in unsustainable exploita-
tion of natural resources, which some have seen as
a warning for the rest of us (Bahn and Flenley 1992).
Environmental degradation has actually been
widespread across the Pacific, and has been linked
to both Polynesian and European expansion (Nunn
1990, 1994; Diamond 1991b). Habitat changes are
hard to separate from other negative influences, but
there is no doubt that the reduction in area of par-
ticular habitats (notably forest) and the disturbance
of that which remains, have been potent forces in
the reduction and loss of numerous island
endemics (Steadman 1997a,b). A specific example is
the loss of the four-coloured flowerpecker (Dicaeum
quadricolor) following the almost complete defor-
estation of the island of Cebú in the Philippines
(Johnson and Stattersfield 1990).
A popular image of pre-industrial hunter-gather-
ers and neolithic agriculturalists is that such peo-
ples lived in harmony with their environment,
practising a conservation ethic and avoiding the
exploitative destruction (‘development’) typical of
later, industrial societies. This idea is associated
with notions of the ‘noble savage’ and a mythical
‘golden age’ (Milberg and Tyrberg 1993). Sadly, the
evidence for widespread degradation of island
ecosystems across the world before they had any
contact with modern European societies is now
overwhelming (e.g. Nunn 1990; Diamond 1991b;
Milberg and Tyrberg 1993; Schüle 1993; Diamond
2005).
Prehistoric humans on islands, although depend-
ent on limited animal resources, regularly failed to
exploit these in a sustainable way. Several cases
where human populations disappeared altogether
from Pacific islands were due to overexploitation of
natural resources, including animals, vegetation
and soils (Diamond 2005). It thus seems likely that
the Polynesian taboo system, which prevents over-
exploitation, was started as a result of the extinc-
tions and misuse of other resources, such that the
‘ecological balance’ only applied to biota that could
not be profitably overexploited with the available
technology and that could survive habitat destruc-
tion and the introduction of rats, dogs, and pigs
(Rudge 1989; Bahn and Flenley 1992; Milberg and
Tyrberg 1993; Benton and Spencer 1995). Indeed,
Pimmet al. (1995) estimate that the first colonists
typically wiped out about half of the native avi-
fauna of an average Pacific island. Yet, there is also
a danger that some extinctions may be falsely
attributed to the first colonists, because intensive
collection often began half a century or so after the
damage initiated by European discovery.
Furthermore, while in many systems it appears that
the first colonists had eventually reached some sort
of balance with the native faunas and floras, ongo-
ing processes of globalization continue to imperil
many oceanic island species.11.5 Trends in the causes of decline
It is easiest to identify trends in the nature of the
threat with reference to island birds, for which the
most systematic assessments have been carried out.
In prehistoric times most losses can be attributed to
hunting, followed by the introduction of commen-
sal species. Over the last 400 years, it appears that
introduced species, followed by hunting, have been
the key forces (Table 11.4). In the contemporary era,
Johnson and Stattersfield (1990) cite habitat loss in
respect to over half the threatened island bird
species, with exotic species the principal threat in a
fifth of the cases. Many of the potential introduc-
tions of predators to once predator-free islands
have already occurred and in at least some cases the
impacts of exotics are being mediated by protection
measures. However, it remains the case that many
of the most severely threatened bird species are
endangered by exotics (e.g. Box 11.3). Alien species
also continue to pose a severe threat to other island302 ANTHROPOGENIC LOSSES AND THREATS TO ISLAND ECOSYSTEMS