wolf predation





Effects of Wolf Predation

Abstract: 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