Biology Reference
In-Depth Information
absence of other rodents, but the length of the upper row of molar teeth
tended to increase as the number of co-occurring rodents increased.Thus,
competitive relationships among these species apparently affected their
patterns of evolutionary change.
Several cases of rapid evolution by predatory mammals introduced to
or invading new geographical areas have been documented, including the
example of the small Indian mongoose discussed at the beginning of the
chapter. A similar case involves the shorttail weasel or stoat (
Mustela
erminea
). Beginning in 1884, European stoats were introduced to New
Zealand from Great Britain in the hope of controlling the European rab-
bit (
Oryctolagus cuniculus
).They are now distributed throughout the coun-
try (King 1991). In New Zealand, the mammalian prey of stoats consists
of few small but many large prey, compared to their diet in Britain. Much
of their prey consists of European rabbits, European hares (
Lepus
europaeus
), brushtail possums (
Tr ichosurus vulpecula
), and rats (
Rattus
spp.),
whereas various species of mice are more important in Britain.This prey
shift is correlated with an increase in the body size and skull length of
stoats, especially females, in New Zealand. In addition, within New
Zealand there is a strong correlation of body weight of stoats with an
index of the size of the prey taken in local areas.
In North America, the coyote (
Canis latrans
) may have evolved rapidly
in body size as it has spread eastward over the past century. From their
original range in the Great Plains, coyotes have spread eastward through
southern Canada and the northern United States to occupy most of New
England. As we noted in chapter 5, animals in this eastern region tend to
be larger and heavier, with males in New Hampshire being about 50%
heavier and females 70% heavier than animals in Colorado (Silver and Sil-
ver 1969; Thurber and Peterson 1991). In New England, their prey
includes adult white-tailed deer (
Odocoileus virginianus
) to a greater extent
than in western parts of their range. Larivière and Crête (1993) suggested
that the larger size of eastern coyotes is genetically based and either the
result of selection for improved ability to hunt larger prey or a favorable
consequence of hybridization with the gray wolf (
Canis lupus
) or possibly
the red wolf (
C. rufus
).
Recent studies by Paul Wilson (Derr 2002) concluded that eastern
gray and red wolves are conspecific and represent an entity that should be
called the eastern wolf (
Canis lycaon
). He also concluded that the large-
bodied eastern population of the coyote is the result of hybridization
between coyotes and the eastern wolf.
