concentrate in less apparent taxa (beetles, and the
like), it is understood that many undiscovered
species remain for collectors and taxonomists
among these relatively cryptic taxa. Only slightly
more surprising is the number of vertebrates scien-
tifically discovered only in recent years on under-
researched islands such as the Philippines (cf.
Heaneyet al. 2005). Even in birds, probably the best-
studied vertebrate group, ‘new’ species have been
described in very recent times in remote islands, e.g.
the flightless rail, Gallirallus rovianae, endemic to the
Solomon Islands and first collected in 1977
(Diamond 1991a). Moreover, in the Canaries, which
might be expected to be very well known scientifi-
cally, two quite sizeable endemic lizards new to sci-
ence but of cryptic habits were discovered during
the 1990s, Gallotia intermediaon Tenerife (Hernández
et al. 2000) and Gallotia gomeranaon La Gomera
(Valido et al. 2000). Following the first discovery of
G. intermediain the Teno peninsular of Tenerife, a
further population was found in another location
adjacent to a teeming tourist resort.
Turning to already extinct island species, Schüle
(1993) summarizes recent studies of vertebrate
endemism for the Mediterranean islands, noting
that although the small-animal faunas have shown
good persistence, the larger terrestrial vertebrates
of the early part of the Quaternary appear to have
included endemic ungulates, carnivores, giant
rodents, tortoises, and flightless swans, not one of
which has survived to the present day. He regards
it as plausible that some of the losses could be
attributed to the arrival of new species driving
older endemic species to extinction by competition.
However, it is increasingly clear that some of this
flux can be attributed to climatic change, sea-level
change, and other environmental forcing factors
(e.g. occasionally volcanism) that exposed the exist-
ing island assemblages both to substantial environ-
mental change and to new colonists (Marra 2005).
From the Late Pleistocene onwards, and especially
in the Holocene, the extinctions—which included
species of pigmy elephants, hippos and cervids,
flightless swans, tortoises, and rodents—are often
attributable to the arrival of humans (Schüle 1993;
Blondel and Aronson 1999), although Marra (2005)
cautions that we still have an incompletefurther than the Bismarcks, and the 18 species of
native rodents no further than the Bismarck or
Solomon islands where 14 of the 18 species are
endemics (Carvajal and Adler 2005). The remain-
ing native mammal species indicated in Table 3.4
are all bats. Variation in richness in the mammal
data appeared explicable as a function of a com-
bination of intraarchipelago speciation in archi-
pelagos of large islands, and interarchipelago
speciation, particularly among more isolated
archipelagos.
To summarize, while different taxa have radiated
to different degrees on particular islands or archi-
pelagos, it appears to be the case that the greatest
degree of endemism is found towards the extremity
of the dispersal range of each taxon (the ‘radiation
zone’sensuMacArthur and Wilson 1967). Islands
that are large, high, and remote typically have
the highest proportion of endemics. In total,
islands account for significant slices of the global
biodiversity cake.
3.5 Cryptic and extinct island endemics: a cautionary note
The foregoing account has taken little note of the
‘state of health’ of island endemics, and some of the
assessments reviewed have included many highly
endangered species and others already believed to
be extinct. Before moving on from the geography of
endemism to an examination of the theories that
may account for the patterns of island ecology and
evolution, it is important to consider both the prob-
lem of rare cryptic forms and the extent of the
losses already suffered. Otherwise, there may be a
danger of misinterpreting evolutionary patterns
that are just the more resistant fragments of for-
merly rather different tapestries (Pregill and Olsen
1981; Pregill 1986). The role of humans in reducing
island endemics to threatened status or extinction is
important enough to warrant a separate chapter
(Chapter 11) but for the moment these examples
can serve to place a health warning on attempts to
explain current suites of endemic species on
islands.
Given the vast number of islands, especially in
the tropics, and the general tendency for diversity to
CRYPTIC AND EXTINCT ISLAND ENDEMICS: A CAUTIONARY NOTE 71