Image from: https://www.nps.gov/yell/learn/nature/wolves.htm
Reintroducing the gray wolf to Yellowstone National Park had a swift and successful effect on the ecosystem. The most immediate effects were felt by the wolves direct prey. Elk, the wolves primary prey, saw greater population management which drove their numbers down to more manageable levels. However, wolves preference for elk was underestimated and as a result more than double the predicted number of elk were killed (Peglar). This drew concerns that the wolves may be too effective at maintaining elk populations which could lead to further imbalances in the local trophic system. The situation was further complicated by interference by cougars and bears. Both cougars and bears had higher elk predation levels than had been expected at the beginning of the project, with bear predation increasing despite stable populations and cougar competition with wolves (Boyce). Due to these unexpected falls in elk populations, bison numbers grew thanks to the fall in competition – even replacing elk as the dominant herbivore in Yellowstone’s Northern Range (Willis). However, elk are still preferred which leads to problems that will be further discussed on the controversies page.
Image from: https://www.yellowstonepark.com/things-to-do/gray-wolves-impact-elk
While the predator-prey relationship between wolves and elk became more complicated than was bargained for, Yellowstone’s ecosystem recovered in many ways thanks to the wolf’s reintroduction. The elk had previously overgrazed Yellowstone, leading to the decline of several plant species such as willow, cottonwood, and aspen that once thrived in the park. With wolves leading to decreased grazing by both elk and bison, willows saw a growth increase in 17 sites across Yellowstone’s Northern Range (Boyce). This particular trophic cascade also brought about the reemergence of a previously diminished animal population: the beaver. Willows are a critical piece for beavers building their dams and ponds, especially in winter months (Farquhar). The cascade continues from here because beaver intervention in waterways affects hydrology which can control runoff and provide a better habitat for fish populations to thrive (Farquhar). This effect continues throughout interacting pieces of the ecosystem. The far-reaching influence of wolf reintroduction, beyond that of the initial predator-prey relationship of focus, illustrates the benefits natural ecosystems could see if similar top-down approaches are implemented elsewhere.
Despite the successful trophic cascade in Yellowstone, researchers warn that the same results cannot and should not be expected in all ecosystems. The data and results of the reintroduction project are exciting, but overextending the results to non-protected areas would likely yield different outcomes (Boyce). The reasoning behind this is that wildlife would have to not only adapt to their new ecosystems but also interact with human activity. This would lend increasing complications and likely a host of public backlash, misinformation, and fear. Building off of that, some scientists argue that the terminology used in these projects is crucial to its success. For instance, “rewilding” and “restoration” are terms often used interchangeably but can complicate policy, practice, and overall scientific communication (Hayward). As a result, consolidating the language used in these cases could lend to easier – and therefore more successful – implementation of these kinds of projects.
Go to the controversies page to learn more.
References:
Boyce, Mark S. “Wolves for Yellowstone: Dynamics in Time and Space.” Journal of Mammalogy, vol. 99, no. 5, 2018, pp. 1021–1031., doi:10.1093/jmammal/gyy115.
Farquhar, Brodie. “Wolf Reintroduction Changes Ecosystem.” Yellowstone National Park Tips, 15 Jan. 2019, www.yellowstonepark.com/things-to-do/wolf-reintroduction-changes-ecosystem.
Hayward, Matt W., et al. “Reintroducing Rewilding to Restoration – Rejecting the Search for Novelty.” Biological Conservation, vol. 233, 2019, pp. 255–259., doi:10.1016/j.biocon.2019.03.011.
Peglar, Tori. “1995 Reintroduction of Wolves in Yellowstone.” Yellowstone National Park Tips, 19 Sept. 2019, www.yellowstonepark.com/park/yellowstone-wolves-reintroduction.
Willis, Katie. “Letting Nature Take Its Course: Wolves in Yellowstone National Park.” Phys.org, Phys.org, 16 Oct. 2018, phys.org/news/2018-10-nature-wolves-yellowstone-national.html.