PATTERNS OF LOSS ACROSS ISLAND TAXA 315times) the introduction of exotic species.
Knowledge of the precise timings of species disap-
pearances is fragmentary, but it does appear that a
number of species disappeared during the
Amerindian period, including at least one species
of ground sloth, whereas other species undoubt-
edly survived to post-Columbian times, including
several species of rodent.
Island snails
Snail extinctions from islands appear to be largely
attributable to two factors—the loss of habitat, and
the introduction of exotic species, mostly preda-
tory snails or ants. The endodontoid snails are tiny
tropical land snails, only a few millimetres in
diameter. Over 600 species have been described
from the Pacific, but one in six of them is thought
to have gone extinct during the twentieth century
(Groombridge 1992). They are mainly ground
dwellers in primary forest, and they are threat-
ened by habitat loss and by introduced ants that
prey on their eggs. Other important island fami-
lies are entirely or largely arboreal, e.g. the
Partulidae, a restrictively Pacific family of some
120 species, most of which are considered to be
threatened. On Hawaii, populations of
achatinelline snails have been lost because of their
low fecundity combined with over-collecting and
habitat modification. In the Caribbean and New
Caledonia it is reported that land snails most at
risk are those in dry lowland forests, which may
be lost more rapidly than upland forest to
causes such as cattle grazing and other forms of
development. In New Zealand, there are many
very localized endemic snails that are entirely
dependent on native plant associations and which
are rapidly being lost. On Madeira, in the eastern
Atlantic, it is reported that of 34 species of land
snails present in samples of varying ages, 9 have
become extinct since human settlement in AD1419,
principally, it seems, as a result of habitat loss
(Goodfriendet al. 1994). Finally, there is evidence
of at least 19 extinct snail species from the
Canaries, although there is some uncertainty as to
whether these losses are attributable to humans or
to past climate change (Izquierdo et al. 2004).
Griffiths et al. (1993) have studied the diet of the
introduced snail Euglandina roseain Mauritius,
where it was released in the hope that it would con-
trol introduced giant African snails, Achatinaspp.
As in some other cases of failed biological control
schemes, the introduced predator ignored the tar-
get species and instead gorged on native snail
species. Some 30% of Mauritian snails are now
extinct. As most losses pre-dated the introduction
ofEuglandina, they have been attributed principally
to habitat destruction, but the exotic predator now
represents one of the major threats to the remaining
endemic snail species. On Hawaii, the introduction
ofEuglandinahas been implicated in the decline of
44 species of endemic Achatinella; and it has been a
major factor in the extinction of Partulaspecies in
French Polynesia, 9 species being lost from Moorea
alone. Thus far, on Mauritius, primary forests do
not appear to have been penetrated by the exoticTable 11.7Native West Indian land mammals known from living or fossil records from
the past 20 000 years (source: Morgan and Woods 1986)
Order Total number Living Extinct % extinction
of species species species
Non-volant groups
Rodentia 45 7 38 84
Insectivora 12 2 10 83
Edentata 16 0 3 100
Primates 3 0 3 100
Volant group
Chiroptera 59 51 8 14
Total 135 60 75 56