Biology Reference
In-Depth Information
Table 8.1. Characteristics of populations of western
mosquitofish in four springs in Nevada after translocation
from a population at Fallon, Nevada. (Data from
Stockwell and Weeks 1999.)
Temperature
Length at
Spring
range (°C)
maturity (mm)
Fat content (%)
#1
34-36
22-26
11-16
#2
34
20-21
14-22
#3
28
19-22
8-10
#4
12-40
16-18
6-7
to the subarctic in North America. Populations show a gradient of body
size from large in northern localities to small in southern areas.This pat-
tern, which follows Bergman's Rule of increasing body size of warm-
blooded animals in colder regions, is usually interpreted to be adaptive in
body temperature regulation (Johnston and Selander 1964; Johnson and
Klitz 1977).This body size gradient appears to have a strong genetic com-
ponent.Adjustment of basal metabolic rate to prevailing local temperature
is also evident (Blem 1974; Kendeigh and Blem 1974).
The action of natural selection on house sparrows can be seen in com-
parisons of individuals surviving severe Kansas winter conditions with
birds present in the preceding fall (Johnston and Fleischer 1981; Fleischer
and Johnston 1982). The winter of 1978-79 in Kansas was one of the
coldest and most snowy on record. Males surviving winter conditions
were significantly larger and females significantly smaller than birds in the
previous fall (Johnston and Fleischer 1981). For males, this is in agreement
with Bergman's Rule, but for females other factors must be important.
Both males and females also showed a decreased surface to mass ratio,
however, which presumably promoted lower metabolic heat loss (Fleis-
cher and Johnston 1982).
The house finch ( Carpodacus mexicanus ), native to western North
America, has provided a particularly interesting case of rapid evolutionary
change following its recent introduction to and colonization of new areas
(Able and Belthoff 1998; Badyaev and Hill 2000).This species was intro-
duced to Hawaii sometime between 1850 and 1870. In 1940, house
finches were released on Long Island, NewYork, by a bird dealer. Between
1960 and 1990, this population spread over much of eastern North Amer-
ica, reaching Michigan and Alabama by 1981. In western North America,
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