amplitude than long-term variation, i.e. the variance
within decades is less than the variance within cen-
turies, which is again less than the variance within
millennia. This can be summed up in the phrase:
climatic variation has a reddened spectrum. Within
large landmasses one important way in which
species respond to high-amplitude climate change
is by range displacement. The possibilities for this
mode of response within isolated oceanic islands
are of course limited, with the corollary that per-
sistent island endemic forms must find environ-
ments they can cope with within the limited
confines of their island(s). If remote islands have
indeed experienced pronounced climate change
within the last two or three million years, has this
driven enhanced extinctions on islands, or has it
selected for broad-niched, adaptable genotypes? At
present, we don’t have the data to answer these
questions.
Over the past several million years, the global
climate system has undergone continual change,
most dramatically illustrated by the glacial–
interglacial cycles of the Pleistocene (e.g. Bell and
Walker 1992). For much of the last glacial period,
for instance, large areas of the British Isles resem-
bled arctic tundra, while the northern and western
regions supported extensive glacial ice. Subpolar
islands such as the Aleutians (north Pacific) and
Marion Islands (south-west Indian Ocean) also
supported extensive icecaps at the last glacial
maximum, and there is evidence that the
Pleistocene cold phases caused extinction of plant
species on remote high-latitude islands, such as
the sub-Antarctic Kerguelen (Moore 1979). The
classical model of four major Pleistocene glacia-
tions has long been replaced by an appreciation
that there have been multiple changes between
glacial and interglacial conditions over the past
2 million years (Bell and Walker 1992). Although
high-latitude islands have been the most dramati-
cally affected by these climatic oscillations, it
would be unwarranted to assume that low-
latitude oceanic islands have been so effectively
buffered that their climates have been essentially
stable.
The Galápagos Islands are desert-like in
their lower regions, with moist forests in the
highlands; however, palaeoenvironmental data
from lacustrine sediments demonstrate that the
highlands were dry during the last glacial period.
The moist conditions returned to the highlands
about 10 000BP, but the pollen data for El Junco
lake on Isla de San Cristóbal indicate a lag of some
500–1000 years before vegetation similar to that of
the present day occupied the moist high ground
(Colinvaux 1972). This delay may reflect the slow
progress of primary succession after expansion
from relict populations in limited refugia in more
moist valleys, or the necessity of many plants hav-
ing to disperse over great expanses of ocean (the
group is approximately 1000 km west of mainland
Ecuador) to reach the archipelago.
Analyses of pollen cores from subtropical Easter
Island also show the local effects of global climate
change. The data indicate fluctuating climate
between 38 000 and 26 000BP, cooler and drier
conditions than those of the present day between
26 000 and 12 000 BP, and the Holocene being gen-
erally warm and moist, but with some drier
phases (Flenley et al. 1991). Contrary to the evi-
dence from Easter Island and the Galápagos, it
appears from studies of snowline changes on trop-
ical Hawaii that conditions were both cooler and,
quite possibly, wetter during the last glaciation
(Vitousek et al. 1995). Given the dominant influ-
ence of ocean and atmospheric current systems on
the climates of oceanic islands (below), it is
unwise to assume a straightforward relationship
between continental and island climate change
over the Quaternary.The developmental history of the Canaries, Hawaii, and Jamaica
The Canaries
The Canaries constitute a comparatively ancient
system for an oceanic archipelago. The increasingly
well-specified geological history provides a crucial
background to understanding the biogeography of
these islands, and the distributions of the many
regional, archipelagic, and single-island endemic
species. The oldest basaltic shields (Northern,
Betancuria, and Jandía) of the island of
Fuerteventura are estimated to have emergedENVIRONMENTAL CHANGES OVER LONG TIMESCALES 27