food supply. Neither bird species invested much
energy in reproduction during the ENSO event
compared with subsequent years. The poor breed-
ing seasons in this study contrast dramatically with
the greatly enhanced reproductive success of land
birds on the Galápagos, which benefited from
improved plant growth and seed production
enabled by the high rainfall (Gibbs and Grant 1987).
Very heavy rainfall stimulated the production of
plants and therefore the caterpillars feeding on
them, important to finches in the breeding season.
A significant increase took place in the population
size of Darwin’s ground finch on Daphne Major
island. Gibbs and Grant (1987) concluded that rare
events can have a major influence on key
population processes, including processes of signif-
icance to evolutionary changes, in long-lived birds
living in temporally varying environments (see also
Grant 1986). These events did not involve species
gains and losses, but warranted attention from
ecologists because of the importance of the endemic
species involved.
Whittaker (1995) argued that island endemics are
unlikely to be lost very often in response to even
large-scale disturbances, such as hurricanes or
volcanic eruptions. First, this is because species and
ecosystems have evolved within the context of the
disturbance regimes. Secondly, and linked to this,
they tend to occur on larger oceanic islands, which
may well provide refuges unaffected by the pertur-
bation somewhere within their land area. A recent
illustration comes in the impact of the eruption of
Chances peak in the 1990s on the endemic
Montserrat oriole. The eruptions led to the loss of
the species from a substantial part of the range, but
sampling indicated that some 4000 individuals
persisted in the less badly affected Centre Hills area
(Arendt et al. 1999). By this line of thinking, small
oceanic islands, such as cays and atolls, should
support relatively impoverished systems with few
endemics restricted to them.
Support for this general line of reasoning is
provided by a study of the Laysan finch (Telespiza
cantans), one of the endangered Hawaiian honey-
creepers. It occurs on the small coral island of
Laysan in the Hawaiian archipelago, although in
prehistorical times it also occurred on Oahu and
Molokai, and a small population has recently been
introduced to Pearl and Hermes reef. Laysan is
only 397 ha in area and of that only 47% is vege-
tated. Morin (1992) found that weather conditions
played a crucial role in regulating reproductive suc-
cess. In 1986, a severe storm caused almost total
mortality of eggs and chicks regardless of clutch
size. Later that year, the number of fledglings per
nest increased as clutch size increased. The species
is omnivorous and eats some part of almost every
plant on the island, as well as invertebrates, carrion,
and eggs. It also has life-history parameters condi-
tioned by long experience of the fluctuating condi-
tions on the island. Reproduction can be spread
over a long breeding season, with the potential for
multiple broods, and the species has a long repro-
ductive lifespan. Notwithstanding this flexibility of
response, it was concluded that stochastic weather
events and predation are the two key factors cur-
rently limiting the Laysan finch population, in con-
trast to most of the other honeycreepers of Hawaii,
whose populations are threatened principally and
acutely by introduced disease carried by exotic
mosquitoes (Pratt 2005).
The South Pacific islands of Samoa have two fly-
ing fox (fruit bat) species, Pteropus samoensis
(endemic to Samoa and Fiji) and Pteropus tonganus.
Piersonet al. (1996) discuss the response of each of
them to two severe cyclonic storms, Ofa, which
struck in 1990, and Val, in 1991. Flying foxes are
important elements of the ecosystem, possibly war-
ranting keystone status, because of their roles as
seed dispersers and plant pollinators. Activity pat-
terns and foraging behaviour were disrupted for
both species. Before the hurricanes P. tonganuswas
much the commoner, with a population on the
small island of Tutuila of about 12 000, contrasting
with fewer than 700 P. samoensisindividuals, and it
was thought that the more restricted endemic
might be the more vulnerable to storm effects.
However, the endemic species was found to have
survival strategies not observed in the more
common and widely distributed P. tonganus, and
the latter experienced the more severe declines, of
the order of 66–99% per colony. The numbers of
P. samoensisseemed to be relatively unaffected. Its
survival strategies included making greater use of160 SCALE AND ISLAND ECOLOGICAL THEORY: TOWARDS A NEW SYNTHESIS