Re-colonizing Carnivores and Naive Prey; Conservation Lessons from Pleistocene Extinctions.

Authors(s): J. Berger, J. E. Swenson and I. Per-Ilson

Publication: Science

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Publication Date: 0000-00-00

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Abstract: The current extinction of many of earth's large terrestrial carnivores has left some extant prey species lacking knowledge about contemporary predators, a situation roughly parallel to that 10,000 to 50,000 years ago, when naive animals first encountered colonizing human hunters. Along present-day carnivore recolonization fronts, brown (also called grizzly) bears killed adult moose at disproportionately high rates in Scandinavia, and moose mothers who lost juveniles to recolonizing wolves in North America's Yellowstone region developed hypersensitivity to wolf howls. Although prey that had been unfamiliar with dangerous predators for as few as 50 to 130 years were highly vulnerable to initial encounters, behavioral adjustments to reduce predation transpired within a single generation. The fact that at least one prey species quickly learns to be wary of restored carnivores should negate fears about localized prey extinction. The spectacular post-Pleistocene extinctions of many genera of large animals in areas ranging from Australia to North America have been attributed primarily to human overkill as hunters encountered naive prey--the "blitzkrieg hypothesis" (1)--and/or to climate change (2). An inadvertent consequence of today's extinction of many large carnivores is that prey in otherwise intact areas may lose knowledge about current predators (3,4). These extinctions, however, offer opportunities to assess the generality of components of the blitzkrieg hypothesis and to address concerns about the ecological consequences of carnivore restoration. In Western Europe and the United States (outside of Alaska), wolves (Canis lupus) and brown bears (Ursus arctos) were eliminated within 100 years from more than 95% of their range. The cessation of Predation has released mammalian prey from past selection pressures (3-5), but the current expansion of large carnivores into formerly depopulated ecosystems is bringing them into contact with naive prey, a situation roughly similar to some post-Pleistocene events. Whereas naive large animals first encountered colonizing paleolithic hunters 10,000 to 50,000 years ago, species such as bison, moose, and elk are now reexperiencing bears and wolves after they had been locally extinct. To understand the possible susceptibility of extant prey to unfamiliar predators, we focus on two predictions: that naive prey (i) fail to display appropriate behavior to reduce predation and (ii) experience heightened mortality along colonizing fronts (6). We studied a common circumpolar ungulate, the moose (Alces alces), focusing on sites (i) with predators, (ii) lacking predators, and (iii) with recent carnivore recolinazation. Two types of macrogeographic contrasts were made: one in Europe, the other in North America. Three Scandinavian sites [(i) Dalarma-Hedmark (Sweden-Norway), (ii) Harjedalen (Sweden). and (iii) Norrbotten (Sweden)] had predatornaive moose that were becoming reexposed to bears along colonizing fronts (7,8). In the United States, six sites (four ia Alaska and two in Wyoming) were studied. The Wyoming sites icluded naive moose in and away from the paths of colonizing wolves and grizzly bears in the southern region of the Greater Yellowstone Ecosystem. Bears. wolves, and moose have overlapped in mainland Alaska for about 9000 years (9), and in these and other systems, juvenile moose mortality is three times greater than when these predators are absent (10,11). Predator-naive individuals may be less sensitive to cues that signify the presence of dangerous carnivores. We examined this idea by comparing (i) vigilance. (ii) predator-directed aggression, and (iii) abandonment of feeding sites by adult female moose during and after systematic playback experiments with novel and familiar auditory and olfactory cues. In Alaska, we used three sites with intact carnivore communities (Talkeetna Mountains, Denali National Park and Preserve, and Matanuska Valley) and three predator-free systems (Kalgin Island in Alaska's Cook Inlet, Grand Teton National Park, and adjacent forest lands): in the latter, prey had not experienced grizzly bears or wolves for 40 to 75 years (12).

Keywords: Greater Yellowstone Ecosystem, animal, mammal, ungulate, moose, bear, grizzly bear, wolf, canine, behavior, carnivore, predation, conservation, restoration, carnivore re-colonization , Cervidae, Alces alces, Ursidae, Ursus arctos horribilis, Canidae, Canis lupus