![]() ![]() They did such a good job that the places apex predators could be found contracted by almost half, according to a formative 2004 study by Andrea S. And so European settlers went to work, destroying the forested refuges of these large and dangerous pests, shooting and poisoning and snaring whatever apex predator they could catch. “Large predatory animals, destructive to livestock and to game, no longer have a place in our advancing civilization,” said E. Manifest destiny had decreed that it was humankind’s responsibility to “tame” North America’s uncivilized wilderness. Wolves and bears and pumas were dangers, not only to their lives, but to their livelihoods as ranchers and their recreation as hunters. “The whole continent was one continued dismal wilderness, the haunt of wolves and bears and more savage men,” John Adams wrote in his journal in 1756. The same kangaroo rats that remain in their burrows one night for fear of the illuminating moonlight will spend hours foraging freely the next if clouds happen to extinguish the light that makes them visible to predators. Because fear works on a moment-to-moment basis, it is infinitely more reactive when compared to slower evolutionary processes. Due to how tightly tied each individual is to another in the web of life, changes in the behavior of one species influence the behavior of another, influencing the behavior of another, on and on, spreading out like ripples on a still pond. Tiny silver fish in dark Norwegian waters changed the depth at which they schooled with the lengthening of the days to stay safely hidden from larger fish. Kenyan zebras that avoided woodland patches during the day-when lions used them-rested in them at night. Studies show that kangaroo rats in New Mexico avoided searching for food on particularly moonlit nights, terrified of death from above in the form of ghostly owls. It wasn’t only wolves that were striking fear into the hearts of prey animals, and it wasn’t only in Yellowstone. Ripple and colleagues of Oregon State University found that the mere presence of wolves scared bison and elk into avoiding riparian areas, allowing overbrowsed species such as willows and aspen to regenerate (although a competing hypothesis claims the simultaneous rise in the local beaver population was the cause). Wolves are also large enough-and numerous enough, compared to the solitary puma-to kill adult elk and bison, allowing them to regulate ungulate populations more effectively. They chase down their prey, and need open habitats to do so. Wolves, however, are not ambush predators. Coyotes are not large enough to kill elk and bison, and although pumas are large enough to kill elk on occasion, the large ungulates could easily avoid pumas by choosing to browse in open habitats-such as delicate riparian areas-that would stymie an ambush predator. ![]() Yellowstone was not predator-free prior to wolf reintroduction, but there were ecologically important differences between those other predators and wolves. In the decade following Brown’s foundational work, a flurry of papers came out, bolstered by the reintroduction of wolves into Yellowstone National Park. Due to the lack of wildflowers in the open meadows-wildflowers that were perhaps the star attraction for a national park-tourists might stop coming, taking their vital admission fees with them. The forest interiors might become too overgrown, pushing out birds that require open understory, such as ovenbirds but the lack of mule deer might also allow oak seedlings to grow to maturity, regenerating the forest canopy. Wildflowers that native pollinators require might decline in the meadows, reducing the numbers of insects that sustain frogs and songbirds, in turn reducing the predators that eat them. If enough mule deer avoid the forest interior for the safety of an open meadow, they will eat more plants in the open meadow than the forest, which would change the vegetation structure of both areas. Imagine the following series of events: To avoid being eaten by a puma, a mule deer might avoid the forest interior for an open meadow, where an ambush predator would find it hard to hide. The idea that an organism might be afraid of being eaten is intuitive, but conceptualizing fear ecology allowed researchers to follow that intuition to its logical-or even surprising-conclusions.
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