Paired Passage Practice PDF

## Passage 1 In the early 2000s, wolves began to drift down from Canada and across the border from Idaho into Washington State. This natural wolf recolonization inspired ecologists such as William Ripple and his colleagues to conduct an exercise in scientific thinking to consider potential impacts...

## Passage 1 In the early 2000s, wolves began to drift down from Canada and across the border from Idaho into Washington State. This natural wolf recolonization inspired ecologists such as William Ripple and his colleagues to conduct an exercise in scientific thinking to consider potential impacts that an apex predator like the wolf would have on the intricate workings of the lynx-snowshoe hare food web. At the time, Washington had low hare and lynx populations and a high coyote population. Coyotes had recently expanded their range and abundance there. Wolves prey on coyotes. What if the wolf's return to the Pacific Northwest could indirectly improve lynx conservation, via trophic cascade effects? Ripple and colleagues hypothesized that two mechanisms would drive wolf-coyote-lynx-snowshoe hare trophic cascades. First, by killing coyotes, wolves would reverse the mesopredator release that had occurred when wolves had been extirpated from this region nearly a century earlier. When humans hunted wolves to extinction, they removed an important check on coyote numbers, creating a "release" on the numbers of this mid-sized predator. Coyote numbers increased, which put more pressure on lynx via competition for food resources such as snowshoe hares. Therefore, by reducing coyotes in this system, a returning wolf population could indirectly create ecological benefits for lynx. The researchers further hypothesized that because coyotes also prey on lynx, a reduction of coyote numbers by wolves would release predation pressure on lynx. Second, in western North America, south of the US-Canada border, wolves prey primarily on elk and deer. When elk and deer numbers are high, these herbivores can suppress shrubs via heavy browsing. Ripple and colleagues hypothesized that the wolf's return would reduce elk and deer numbers and also change their behavior, as has been found in places like Yellowstone by John Laundré and others. Elk and deer need to stay alert in order to survive in areas where wolves exist. This means keeping their heads up and spending less time standing in one spot with their heads down, as they typically do when there are no wolves in a system. Via this predation risk mechanism, wolves could indirectly reduce browsing pressure on shrubs, which would improve snowshoe hare habitat, thereby benefiting lynx. ## Passage 2 Ripple et al. correctly state that wolves can affect coyotes, both behaviorally and ecologically, in the Greater Yellowstone Ecosystem (GYE), as shown by Berger and Gese, and that such regulation can have cascading effects. However, despite the well-publicized initial declines in coyote abundance in the GYE following wolf recovery, coyotes may now be adapting to wolves and coyotye pack numbers may have rebounded. The trophic strength of wolf effects on coyotes may also differ geographically with variation in climate, primary productivity, carnivore and prey communities, and the degree of human persecution. The inverse relationship between wolves and coyotes in Yellowstone is not supported outside the two national parks (Yellowstone and Grand Teton) included in the analyses by Berger and Gese. In other systems where wolves, coyotes, and lynx coexist, research shows a positive relationship between wolves and coyotes, whereby coyotes benefit from scavenging on wolf-killed ungulate carcasses. The generally low mortality rates of radio-collared coyotes killed by wolves outside of Yellowstone in Northwest Montana is three times less than those killed by cougars. Thus, this quick review of the literature suggests that the strongest generality of Ripple et al.'s hypothesis that wolves have a direct negative effect on coyotes is, at best, inconsistent, both within the GYE and across wolf-coyote range in North America. Buskirk et al. hypothesized that coyotes compete with lynx through both interference competition (direct killing or displacement) and indirect exploitave competition for shared food resources. Ripple et al. speculated that these interactions are, in part, responsible for the imperiled status of southern lynx. Unfortunately, evidence for interference competition is essentially limited to anecdotal observations. An observation of a single juvenile lynx killed by a coyote in the Yukon is not prima facie (at first sight) evidence for a trophic-level interaction. Further, in this northern population, more predation mortality of radio-collared lynx was attributed to wolves, wolverines, and other lynx than to coyotes. Direct interactions between coyotes and lynx were rare.