rodents occur on the Solomons and Bismarcks,
neither archipelago being particularly remote from
New Guinea. But for the more remote islands,
beyond the reach of non-volant terrestrial mam-
mals (Table 3.1), mammal representation is
restricted to bats, of which flying foxes are
arguably the most important group, although
other types of bat occur on islands. There are
believed to be 161–174 species of flying fox
(Chiroptera: Pteropodidae) and they are distrib-
uted throughout the Old World Tropics (but not
the New World). In number of species, range, and
population sizes, flying foxes have been the most
successful group of native mammals to colonize
the islands of the Pacific. The Pacific land region
consists of about 25 000 islands, most of them very
small. In addition to occupying small islands, most
flying foxes have restricted distributions. Thirty
eight of the 55 island species occupy land areas of
less than 50 000 km^2 and 22 of these species occupy
land areas of less than 10 000 km^2 ; 35 occur only on
a single island or group of small islands (Wilson
and Graham 1992).Comparisons between taxa at the regional scale
Within the figures cited above, those from G. H.
Adler and his colleagues provide a common
methodological approach and enable comparisons
of patterns of endemism of different taxa at the
regional scale (Table 3.4). The studies are based on
26–30 tropical Pacific Ocean islands or island
archipelagos, plus in one case 14 Indian Ocean
islands/archipelagos. The data include all known
extant species plus others known only from sub-
fossils.
Both birds and butterflies are capable of active
dispersal over long distances and have colonized
virtually every archipelago and major island within
the tropical Pacific. Birds have a higher frequency
of endemism than butterflies. Adler and Dudley
(1994) consider that birds have superior dispersal
ability, and that this might be anticipated to have
maintained higher rates of gene flow than in but-
terflies, contrary to the higher degree of endemism.
One plausible explanation is that the lower rate of
endemism in butterflies might be a consequence of
the constraints of the co-evolutionary ties withcontained fewer species, had lower proportions of
endemics, and had several families that were much
more poorly represented, despite being diverse in
the mainland source areas (Adler 1992). The gener-
ally small size of the Indian Ocean islands may be
significant in these differences. The total land area is
only 7 767 km^2 , compared to 165 975 km^2 for the
Pacific study, and there are also fewer island archi-
pelagos in the Indian Ocean and they tend to be less
isolated. The poor representation of certain families,
notably the ducks and kingfishers, might be due to
a shortage of suitable habitats, such as freshwater
streams and lakes. Intra-archipelago speciation has
been rare in the Indian Ocean avifauna, possibly
occurring once or twice in the Comoros and a few
times in the Mascarenes. Adler (1994) suggests that
there may not be sufficient numbers of large islands
to have promoted intraarchipelago speciation in the
Indian Ocean. In contrast, it has been common
within several Pacific archipelagos, accounting for
most of the endemic avifauna of Hawaii, being
important in the Bismarcks and Solomons, and
occurring at least once in New Caledonia, Fiji, the
Society Islands, Marquesas, Cooks, Tuamotus, and
Carolines. In conclusion, Adler (1994) echoes
Williamson’s (1981) remark in respect of bird speci-
ation on islands that ‘geography is all important’.
Mammals
With the exception of bats, native mammals are not
a feature of the most isolated oceanic islands, but
less isolated islands include many that either once
hosted or still do host interesting assemblages of
native and often of endemic mammals. Perhaps the
most impressive example is the Philippines, an
archipelago of 7000 mostly true oceanic islands, fea-
turing 170 species of mammals in 84 genera, of
which 24 (29%) genera and 111 (64%) species are
endemic (Heaney et al. 2005). Particularly impres-
sive radiations have occurred in fruit bats and
murid rodents, with patterns of endemism in the
non-volant mammals clearly tied to Ice Age
bathymetry, i.e. to the configuration of the islands
as they were during the major low sea-level stands
of the Pleistocene.
In the tropical Pacific, Carvajal and Adler (2005)
note that a number of species of marsupials and
ENDEMISM 69