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martens typically defend territories, with those of males being roughly twice the size

of the female territories that they overlap. Young martens are born in a small litter

in late spring, stay in a den with the mother until late summer or early fall, and then

disperse over large distances seeking out their own breeding territory.

Like many other carnivores (see Chapter 10), marten abundance tends to track

year-to-year changes in their major prey species (snowshoe hares, red-backed voles,

red squirrels, and deermice in Ontario). In the area around Algonquin Provincial Park,

for example, the exponential rate of increase by martens (r) varies four-fold with sim-

ilar scale of variation in their major prey species (Fig. 19.2).

Like many territorial species, however, there is an additional density-dependent

effect of marten numbers on their own annual rate of change, beyond the variation

imposed by the food supply (Fig. 19.3). One explanation for this density dependence

is that dispersing juveniles cannot obtain suitable sites for breeding territories when

marten abundance is high, effectively cutting them off from contributing to further

population growth. A second possibility is that the frequency of deadly aggression

338 Chapter 19

1.0

0.8

0.6

0.4

0.2

0

0 100 200 300 400

Deermouse abundance, Z

Annual rate of increase,

r

Fig. 19.2Year-to-year
variation in the
exponential annual rate
of increase (r) of
martens in the
Bracebridge District near
Algonquin Provincial
Park, Ontario, in
relation to variation in
deermouse abundance
(measured in captures
per 1000 trap-nights).
(After Fryxell et al.
1999, 2001.)

Marten abundance, N

Annual rate of increase,

r

1.0

0.8

0.6

0.4

0.2

0

0 400 600 800 1000

Fig. 19.3Year-to-year
variation in the
exponential annual
rate of increase (r)
of martens in the
Bracebridge District near
Algonquin Provincial
Park, Ontario, in
relation to variation
in marten abundance
(minimum number
alive). (After Fryxell
et al. 1999, 2001.)