Biology Reference
In-Depth Information
produce sprouts.The sprouts survive for a number of years , until they are
attacked and killed. Thus, the American chestnut is not extinct, but it is
no longer an ecologically significant species of the eastern forests. Other
tree species have filled the gap left by the death of the chestnut.The loss
of this species, which was the most important mast-producing tree of the
deciduous forest, probably had a major impact on forest birds and mam-
mals (Campbell and Schlarbaum 1994).
Several other tree diseases, including white pine blister rust (
Cronar-
tium ribicola
), Dutch elm disease (
Ophiostoma ulmi
; see chapter 5), dogwood
anthracnose (
Discula destructiva
), and sudden oak death canker (
Phytoph-
thora ramorum
), also are potential agents of extirpation of native trees.
Recent reports indicate that sudden oak death canker also affects several
other woody plants of the North American Pacific coast, including the
coast redwood (
Sequoia sempervirens
).
Alien diseases are increasing contributors to extirpation of populations
of animals. Crayfish plague, a fungal disease endemic to North America,
has played a major role in the decline of native crayfish in Europe (Lodge
et al. 2000).
Avian pox and avian malaria, brought to Hawaii by the introduction
of alien birds, are now one of the major threats to the remaining endemic
birds.Avian malaria resulted from the introduction both of alien mosquito
vectors and birds carrying the malaria parasites (Scott and Sincock 1985;
van Riper et al. 1986;Warner 1968). More recently, toxoplasmosis, a dis-
ease caused by a parasitic protozoan (
To xoplasma gondii
), has been found in
the 'alala or Hawaiian crow (
Corvus hawaiiensis
), one of the most endan-
gered birds in the world (Work et al. 2000). The definitive host and pri-
mary reservoir of this disease in the wild is the feral domestic cat. The
'alala has been the object of a major reintroduction effort with captive-
bred birds.The eradication of the feral cat population being nearly impos-
sible, this disease poses a very serious problem for 'alala recovery.
Extinction and Extirpation due to Hybridization
Hybridization with alien species is a threat to a number of plants ranging
from grasses and broad-leaved herbs to woody shrubs and trees (Levin et al.
1996; Daehler and Carino 2001). Simulation models of the hybridization
process indicate that it can lead to extinction of native species by aliens in
five or fewer generations (Wolf et al. 2001). A current example is
Lantana
depressa
,a member of the verbena family, which is distributed throughout
peninsular Florida.This diploid species has come into close contact with
L.
