untitled

et al. 1988a) and moose in Finland (Lehtonen 1998) suggest that long-term oscilla-

tions are an important feature of some large mammal species.

Long-term data for a number of other wildlife populations show pronounced cycles,

first identified by Charles Elton (Elton 1924). Such cycles are sometimes regular, such

as the 10-year cycle of snowshoe hares (Sinclair et al. 1993), and other times some-

what erratic, such as the 3– 6-year cycle of voles (Microtus agrestisand Clethrionomys

rufocanus) in northern Europe (Turchin and Hanski 1997). Such cycles can be explained

in many ways. A short list of hypotheses include: unstable behavioral polymorphisms

in cyclic populations (Chitty 1967; Krebs and Myers 1974); maternal effects trans-

ferred to offspring, imparting lagged density dependence (Inchausti and Ginzburg

1998); and coupled interactions between plants, herbivores, and /or carnivores

(Hansson 1987; Turchin and Hanski 1997; Turchin and Ellner 2000; Turchin and

Batzli 2001). We shall review the northern European vole and North American

snowshoe hare populations and consider the logic underlying consumer–resource

explanations for population cycles.

Some of the longest continuous studies of vole populations come from sites in

Scandinavia, Finland, and Russia (Turchin 2003). These data point to a fascinat-

ing geographical pattern: populations at southern latitudes show little evidence of

212 Chapter 12

4.0

3.5

3.0

2.5

2.0

8.0

7.5

7.0

6.5

6.0

0.7

0.5

0.3

0.1

1957 1962 1967 1972 1977 1982 1987 1992 1997

(a)

(b)

(c)

Year

Fir growth (mm)

Moose density

Wolf density

1957 1962 1967 1972 1977 1982 1987 1992 1997

1957 1962 1967 1972 1977 1982 1987 1992 1997

Fig. 12.13Population
dynamics of wolves (a)
and moose (b), as well
as annual growth of
balsam fir trees (c) on
Isle Royale. The solid
lines represent observed
values, the dotted lines
polynomial regressions.
The densities represent
total abundance of each
species recorded over
the entirety of Isle
Royale. (After Post
et al. 1999.)

12.7 Other population cycles