untitled

As we saw in Chapter 6 (see also Chapter 14), it can take many years for age dis-

tributions to stabilize in long-lived organisms. When age distributions are shaped by

dynamic interactions with predators, this can be even more destabilizing. We also

know that the wolf population on Isle Royale has much lower levels of genetic

variability than do populations on the mainland (Wayne et al. 1991). This could

influence wolf demographic parameters in unknown ways. Finally, there is evidence

that complex interactions among climatic conditions, social grouping patterns of wolves,

and predation risk of moose could contribute to instability. In years of deep snow,

wolves form larger packs, which leads to increased rates of mortality on moose (Post

et al. 1999). Nonetheless, the instability of this system seems to be intrinsic to the

basic consumer–resource interactions (moose/vegetation and wolf /moose).

Truly long-term data for temperate zone carnivores (wolves and coyotes) and

ungulates (moose or white-tailed deer, depending on location) are scarce. Data

from the Hudson’s Bay Company probably represent the lengthiest data set. These

data suggest very slow oscillations in the abundance of wolves and coyotes during

1750 –1900, with roughly two cycles per century (Turchin 2003). Although the Hudson’s

Bay data on deer skins are more fragmentary, they too suggest long-term cycles in

abundance (Turchin 2003). Slow oscillations by white-tailed deer in Canada (Fryxell

CONSUMER–RESOURCE DYNAMICS 211

10

1

0.1

0.01

1·10–3

1·10–4

1·10–5

1·10–6

1·10–7

1

0.1

0.01

0 100 200 300 400 500

Year

0 100 200 300 400 500

Year

Wolves / km

2

Moose / km

2

Fig. 12.12Predicted
dynamics of the moose
(top) and wolf (bottom)
system with woody
plants when wolves
have additional density-
dependent mortality due
to territorial aggression,
as described in the text.