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winter survival of birds in Alabama, Michigan, and Montana (Badyaev et
al. 2000). These studies found different responses in the three areas but
showed that the most successful birds of each sex were those with mor-
phological characteristics matching those resulting from selection acting
since the populations were founded.
A number of vertebrates in the Australasian region have shown rapid
evolution following their introduction or invasion of new areas.The gray-
breasted silvereye ( Zosterops lateralis ) expanded its range in the Australasian
region in the 1800s and early 1900s. From Tasmania, the species invaded
South Island, New Zealand in 1830. From there, it spread to Chatham
Island and New Zealand's North Island in 1856 and throughout New
Zealand by 1865. In 1904, it reached Norfolk Island, northwest of New
Zealand. Along this progressive colonization sequence, populations
showed gradual reduction in genetic diversity and increased genetic dif-
ferentiation (Clegg et al. 2002). The changes at each colonization step,
however, were small. Nevertheless, after three or four colonization events,
founder effects and genetic drift led to a degree of differentiation compa-
rable to that of silvereye populations isolated for periods of a few thou-
sand years.
Among mammals, the European rabbit ( Oryctolagus cuniculus ), intro-
duced to Australia in 1859, has evolved differences in body size and ear
shape in different climatic zones (Williams and Moore 1989). These dif-
ferences appear to be related to body temperature regulation. Rapid evo-
lutionary changes also have been noted in several rodents introduced to
oceanic islands (Pergams and Ashley 2001). The house mice ( Mus muscu-
lus ), introduced to the small British islands of Skokholm in about 1907
and Festur in 1939, has shown morphological changes in several charac-
teristics. Black rats ( Rattus rattus ) introduced to the islands of Baltra and
Santa Cruz in the Galapagos, Ecuador, have also shown morphological
divergence in many skeletal characteristics (Patton et al. 1975).
New Zealand is a hot spot of evolutionary adjustments by introduced
land vertebrates, as well as by the chinook salmon discussed earlier. The
common myna ( Acridotheres tristis ), introduced in the late 1800s, shows lat-
itudinal variation in morphology (Baker and Moeed 1979). Several other
alien birds exhibit reduced clutch sizes compared to their native regions
(Yom-Tov et al. 1986). Other European birds introduced in the 1800s
show reduced genetic variability, compared to European populations, that
appears to be the result of founder effects and genetic drift (Ross 1983;
Parkin and Cole 1985; Baker et al. 1990).
The brush-tailed opossum ( Tr ichosurus vulpecula ) was introduced to
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