Biology Reference
In-Depth Information
to oceanic islands has also been the cause of numerous extinctions of
plants and animals. Numerous island plants have been driven to extinc-
tion by habitat conversion and the impacts of introduced mammals. In the
Hawaiian Islands, for example, 80-90 species of plants have become
extinct and about 270 additional species are threatened or endangered (F.
Kraus, personal communication). Many island reptiles have been driven to
extinction by introduced predators (Honegger 1980; Case and Bolger
1991). In particular, the Indian mongoose (
Herpestes auropunctatus
), which
has been introduced to many Pacific and West Indian islands, has extir-
pated many snakes and lizards. Cats have had a serious impact on arboreal
lizards on which mongooses cannot prey.
A striking example of how an alien species can lead to extirpation of
prey species is provided by the brown tree snake (
Boiga irregularis
), intro-
duced to the island of Guam in about 1950 (Rodda et al. 1999).This noc-
turnal predator, native to northern Australia, New Guinea, and neighbor-
ing Pacific islands, is active in both terrestrial and arboreal habitats. No
such predator existed on Guam, so native species were naive prey for the
brown tree snake. Predation by the brown tree snake has been implicated
as the principal cause of extirpation of nine species of forest birds, three
seabirds, and between three and five lizards.
In addition to the impacts of predatory mammals introduced by Poly-
nesians to Pacific islands, including the Hawaiian Islands, invertebrate
predators are taking a toll on native species. Hawaiian tree snails of the
genus
Achatinella
originally included 41 species that evolved on the island
of Oahu. Although reduced in numbers by the effects of habitat destruc-
tion and predation by mammals, the final blow was the introduction of a
predatory rosy wolfsnail (
Euglandina rosea
) in 1958 as a hoped-for biolog-
ical control of the alien giant African snail (
Achatina fulica
). The giant
African snail survives, but more than half of the
Achatinella
snails are now
extinct, and the remaining species are declining (Hadfield 1993). On
Kauai, many endemic snails of the family Amastridae have disappeared
due to predation by
Euglandina
(Civeyrel and Simberloff 1996).
Eugland-
ina
also feeds on native aquatic snails in Hawaii and may be contributing
to their decline (Kinzie 1992).The rosy wolfsnail has been introduced to
other Pacific islands, including American Samoa, where its impact on
native land snails is also severe (Cowie and Cook 2001), and French Poly-
nesia, where many land snail extinctions have occurred (Civeyrel and
Simberloff 1996). On the French Polynesian island of Raiatea, 33 species
of
Partula
have become extinct, and on Moorea, 7 species have been lost
(Coote and Loève 2003). In Hawaii, introduced insects, particularly the
