untitled

Canada shows the clearest (Fig. 8.3), as indicated by the furs collected by trappers

for the Hudson Bay Company over the past two centuries (MacLulich 1937).

This relative constancy of population size, or at least fluctuation within limits, is

in contrast to the intrinsic ability of populations to increase rapidly. The fact that

population increase is limited suggests that there is a mechanism in the population

that slows down the rate of increase and so regulates the population. We discuss first

the theory for how populations might be limitedand regulated.

110 Chapter 8

100

80

60

40

20

0

Females / 100 trap-nights (adjusted)

JFMAMJJASONDJFMAMJJASONDJFMAMJJASOND

1978 1979 1980

Fig. 8.2Density indices
for old female house
mice on contour banks
and in stubble fields of
rice crops in
southeastern Australia.
Broken lines distinguish
the crop cycle cohort of
1978–79 from that of
1977–78 and 1979–80.
The extent of the peak
in January 1980 is
unknown due to a
poisoning campaign.
(After Redhead 1982.)

150 000

100 000

50 000

0

Year

Number of hares

150 000

100 000

50 000

0

1790 1795 1800 1805 1810 18151820 1825 1830 1835 1840 1845 1850 1855 1860

1865 1870 1875 1880 1885 1890 1895 1900 1905 1910 1915 1920 1925 1930 1935

Number of hares

Fig. 8.3Snowshoe hares in the boreal forest of Canada show regular fluctuations in numbers with a 10-year periodicity.
Data are from the Hudson Bay Company fur records up to 1903 and questionnaires thereafter. (After MacLulich 1937.)