Wolf Predation (1961 words)

Wolf Predation
This paper discusses four hypotheses to explain the effects of wolf predation on
prey populations of large ungulates.

The
four proposed hypotheses examined are the predation limiting hypothesis, the
predation regulating hypothesis, the predator pit hypothesis, and the stable
limit cycle hypothesis. There is much research literature that discusses how
these hypotheses can be used to interpret various data sets obtained from field
studies. It was concluded that the predation limiting hypothesis fit most study
cases, but that more research is necessary to account for multiple predator –
multiple prey relationships. The effects of predation can have an enormous
impact on the ecological organization and structure of communities. The
processes of predation affect virtually every species to some degree or another.

Predation can be defined as when members of one species eat (and/or kill) those
of another species. The specific type of predation between wolves and large
ungulates involves carnivores preying on herbivores. Predation can have many
possible effects on the interrelations of populations. To draw any correlations
between the effects of these predator-prey interactions requires studies of a
long duration, and statistical analysis of large data sets representative of the
populations as a whole. Predation could limit the prey distribution and decrease
abundance. Such limitation may be desirable in the case of pest species, or
undesirable to some individuals as with game animals or endangered species.

Predation may also act as a major selective force. The effects of predator prey
coevolution can explain many evolutionary adaptations in both predator and prey
species. The effects of wolf predation on species of large ungulates have proven
to be controversial and elusive. There have been many different models proposed
to describe the processes operating on populations influenced by wolf predation.

Some of the proposed mechanisms include the predation limiting hypothesis, the
predation regulating hypothesis, the predator pit hypothesis, and the stable
limit cycle hypothesis (Boutin 1992). The purpose of this paper is to assess the
empirical data on population dynamics and attempt to determine if one of the
four hypotheses is a better model of the effects of wolf predation on ungulate
population densities. The predation limiting hypothesis proposes that predation
is the primary factor that limits prey density. In this non- equilibrium model
recurrent fluctuations occur in the prey population. This implies that the prey
population does not return to some particular equilibrium after deviation. The
predation limiting hypothesis involves a density independent mechanism. The
mechanism might apply to one prey – one predator systems (Boutin 1992). This
hypothesis predicts that losses of prey due to predation will be large enough to
halt prey population increase. Many studies support the hypothesis that
predation limits prey density. Bergerud et al. (1983) concluded from their study
of the interrelations of wolves and moose in the Pukaskwa National Park that
wolf predation limited, and may have caused a decline in, the moose population,
and that if wolves were eliminated, the moose population would increase until
limited by some other regulatory factor, such as food availability. However,
they go on to point out that this upper limit will not be sustainable, but will
eventually lead to resource depletion and population decline. Seip (1992) found
that high wolf predation on caribou in the Quesnel Lake area resulted in a
decline in the population, while low wolf predation in the Wells Gray Provincial
Park resulted in a slowly increasing population. Wolf predation at the Quesnel
Lake area remained high despite a fifty percent decline in the caribou
population, indicating that mortality due to predation was not density-dependent
within this range of population densities. Dale et al. (1994), in their study of
wolves and caribou in Gates National Park and Preserve, showed that wolf
predation can be an important limiting factor at low caribou population
densities, and may have an anti-regulatory effect. They also state that wolf
predation may affect the distribution and abundance of caribou populations.

Bergerud and Ballard (1988), in their interpretation of the Nelchina caribou
herd case history, said that during and immediately following a reduction in the
wolf population, calf recruitment increased, which should result in a future
caribou population increase. Gasaway et al. (1983) also indicated that wolf
predation can sufficiently increase the rate of mortality in a prey population
to prevent the population’s increase. Even though there has been much support of
this hypothesis, Boutin (1992) suggests that “there is little doubt that
predation is a limiting factor, but in cases where its magnitude has been
measured, it is no greater than other factors such as hunting.” A second
hypothesis about the effects of wolf predation is