One of the most well-known (albeit misunderstood) tales of extinction is that of the dodo; while the birds were capable of defending themselves if necessary, they generally did not fear sailors that came onto the islands. The dodos were beset by an invasion of men, pigs, rats, and other creatures they had no experience with, and the ecological degradation as well as their inability to consider man a predator led to the ultimate demise of the species. I can only wonder if the dodo would have persisted if their pressures upon it were not so acute; would it have learned to be wary of humans? That is a question that cannot be answered, but a new study by Dr. Joel Berger of the WCS has uncovered some surprising insights into predator-prey interactions, revealed in the new paper “Carnivore Repatriation and Holarctic Prey: Narrowing the Deficit in Ecological Effectiveness” in the journal Conservation Biology (and I just canceled my subscription due to lack of service too. Damn!)
Keystone predators have been nearly eradicated in their natural ranges all over the world, wolves, tigers, and brown bears being some of the most notable carnivores. In their absence, new generations of ungulates like moose and deer have never learned what a wolf howl or tiger growl sounds like, and so they have little response to the sounds and smells of predators. Using recordings (and perhaps even urine-soaked snowballs), Berger has found that prey animals typically do not react quickly to various stimulus that would indicate a predator they have no experience with. There have been efforts to reintroduce predators, however, and wolves were successfully brought back to Yellowstone in 1995. When Berger found was that the Bison in Yellowstone had learned to recognize wolf howls, responding even more strongly than bison in other areas that have had constant contact with wolves over many generations, showing that prey animals can indeed learn to fear predators again.
Also of importance is the area in which the prey is located when confronted with signs of a predator; snow depth and distance from cover may make a difference as to how prey reacts. Unfortunately I don’t have access to the whole article, but it sounds absolutely amazing. I can only imagine what it must have been like to undertake such a study; visiting locations all over the world in order to quiet fears that predators will decimate prey populations if introduced. So, I can has grant to continue research?
The continuing global decline of large carnivores has catalyzed great interest in reintroduction to restore populations and to reestablish ecologically functional relationships. I used variation in the distribution of four Holarctic prey species and their behavior as proxies to investigate the pace and intensity by which responses are lost or reinvigorated by carnivore repatriation. By simulating the presence of wolves (Canis lupus), tigers (Panthera tigris), and brown bears (Ursus arctos) at 19 transcontinental sites, I assayed three metrics of prey performance in areas with no large terrestrial carnivores (the polar islands of Greenland and Svalbard), extant native carnivores (Eastern Siberian Shield, boreal Canada, and Alaska); and repatriated carnivores (the Yellowstone region and Rocky Mountains). The loss and reestablishment of large carnivores changed the ecological effectiveness of systems by (1) dampening immediate group benefits, diminishing awareness, and diminishing flight reaction in caribou (Rangifer tarandus) where predation was eliminated and (2) reinstituting sensitivity to carnivores by elk (Cervus elaphus) and moose (Alces alces) in the Yellowstone region to levels observed in Asian elk when sympatric with Siberian tigers and wolves or in Alaskan moose sympatric with wolves. Behavioral compensation to reintroduced carnivores occurred within a single generation, but only the vigilance reaction of bison (Bison bison) in Yellowstone exceeded that of their wolf-exposed conspecifics from boreal Canada. Beyond these overt responses by prey, snow depth and distance to suitably vegetated habitat was related to heightened vigilance in moose and elk, respectively, but only at sites with carnivores. These findings are insufficient to determine whether similar patterns might apply to other species or in areas with alien predators, and they suggest that the presumed excessive vulnerability of naïve prey to repatriated carnivores may be ill-founded. Although behavior offers a proxy to evaluate ecological effectiveness, a continuing challenge will be to understand how naïve prey respond to novel or introduced predators.