lose fear in absence of predators
an elk or a moose standing still, without fear, as a pack of wolves
or a grizzly bear moves in for the kill. It seems unlikely, but
this is a common occurrence in areas where predators are reintroduced
after several generations of absence.
animals tend to forget their fear over time and will often stand
vulnerable to attack. This could threaten their survivability
as a population if their numbers are already stressed. For this
reason, wildlife biologists should carefully assess prey populations
before introducing predators into an ecosystem, says John Gittleman,
associate professor of biology,
in an article published last week in the journal Science.
kill more prey when reintroduced into an ecosystem after several
generations of absence.
165 carnivore reintroductions worldwide, none assessed how prey
populations respond to the reintroduction of predator species,
lack of assessment could be inviting disaster, and may even greatly
increase the risk of extinction for some at-risk prey species,"
he says. "When carnivores are introduced by wildlife managers,
the emphasis is almost always on the survivability of the predator
rather than the prey. But more study is likely needed to make
sure the prey population can be sustained, which in turn, will
sustain the predator population."
species become highly vulnerable when suddenly exposed to a carnivore,"
Gittleman says. "They don't know how to respond when a predator
approaches because they've never experienced an attack." They
often behave as if their evolutionarily developed fear has been
Prey animals in this situation, such as elk and moose, have been
observed standing still allowing a newly introduced wolf population
to simply walk up and make the kill, Gittleman says. Studies have
shown that a disproportionately high level of predation occurs
immediately following the initial introduction of predators to
areas where they had been nonexistent for generations. This ignorance
of danger, when combined with habitat destruction, and overexploitation
of resources in some areas, could reduce some prey populations
to dangerously low levels. Prey animals on islands, which generally
have fragile ecosystems, are particularly vulnerable to predator
can often take some time for prey animals to become aware of what's
happening, and to relearn their fear and sense of caution," Gittleman
says. "Many of them die, initially, as this learning process takes
Gittleman suggests that prey could possibly be trained to relearn
fear by conducting a limited predator introduction before releasing
large numbers of carnivores into the wild.
"It might make sense to send in one lone wolf, so to speak, to
give prey an adjustment period to develop vigilance," Gittleman
says. "Once the prey learns the sound of a wolf call, for example,
and has the proper fear response, then a full introduction of
predators might be appropriate. An assessment of the prey population
would be an important step toward assuring the prey population
is able to sustain the first wave of predation."
an evolutionary biologist who came to U.Va. in 1998, specializes
in problems of biodiversity and extinction. The author of numerous
papers in leading scientific journals, most recently he has co-authored
three papers in Science in less than a year. This Science article
was co-authored with Mathew E. Gompper, a biologist at Columbia
University and a former Gittleman graduate student. They wrote
the article as an invited Perspectives column, putting into broader
context a peer-reviewed study appearing in the same issue.