Biology Reference
In-Depth Information
Table 16.1.
Percentages of native species in the United States threatened by vari-
ous major impacts. (Data from Wilcove et al. 1998.)
Habitat
degradation
Alien species
Pollution
Overexploitation
Disease
All species (1880)
85
49
24
17
3
Ve r tebrates (494)
92
47
46
27
11
Invertebrates (331)
87
27
45
23
0
Plants (1055)
81
57
7
10
1
Mainland (641)
90
30
12
13
1
Hawaii (414)
66
99
0
6
0
Birds (98)
90
69
22
33
37
Mainland (56)
88
48
38
39
4
Hawaii (42)
93
98
2
24
81
dominance of extinctions among island species now may be declining.
Lomolino and Channell (1995) noted that the rate of extinction of con-
tinental mammals per unit time has risen until it almost equals that for
islands. Relative to habitat area or number of species, on the other hand,
mammal extinctions are still higher on islands.
Extinction and Extirpation due to Predation
and Herbivory
The role of alien species in extinction on islands has a long history.
Numerous native birds on Pacific islands, including Hawaii, were driven
to extinction by predation by dogs, pigs, and rats, together with human
hunting, following the arrival of Polynesian colonists (Olson and James
1984; Steadman 1995). In Hawaii alone, about 60 species became extinct
during the Polynesian period. These included flightless species of geese,
ibis, and rails, as well as flying members of several other families. Many of
these species were probably easy prey because of the previous absence of
terrestrial predators. In New Zealand, the kiore (
Rattus exulans
) intro-
duced by Polynesian colonists, has probably been responsible for extirpa-
tion of tuataras (
Sphenodon
spp.), lizards, frogs, and large terrestrial
orthopterans on the mainland and some offshore islands.
More recently, predation and destruction of vegetation following the
introduction of goats, pigs, dogs, cats, rats, mongooses, and other mammals
