Effect of Wolves on the Ecosystem

            Recently, I have been researching the negative effects of wolves on today’s livestock production industry. In this post, I want to explore more in depth the effect that the presence or absence of wolves has on the ecosystem. More specifically, I would like to answer the question, “Are the benefits to the ecosystem worth the cost to the livestock industry to reintroduce wolves in the United States?”

            To learn more about wolves’ contributions to the ecosystem, I read an article published in 2004 entitled “Wolves and the Ecology of Fear: Can Predation Risk Structure Ecosystems?”¹ Although somewhat dated, the science presented in this article is nonetheless accurate and applicable to understanding the effect on the local ecosystem of the extirpation and subsequent reintroduction of wolves in the US. 

            The article begins by summarizing how presence or absence of wolves can magnify to affect large-scale changes on an ecosystem. This occurs through the process of trophic cascades, which are described in the article as the indirect effects of changes at one level of the food chain on organisms at other levels. The presence of wolves has two types of effects on the wolves’ ungulate prey species: lethal and nonlethal. An example of a cascading lethal effect would be the direct killing of ungulates by wolves, resulting in lower ungulate populations. A nonlethal effect would be behavioral changes of the prey species in order to avoid interactions with the predator. 

            Both lethal and nonlethal effects of wolves on herbivores subsequently affects the growth of woody plants, such as willow, aspen, and cottonwood. In the absence of wolves, foraging behaviors and browsing pressure of herbivores limits growth and recruitment of these woody plant species. In the presence of wolves, lower densities and predator-avoidance behavior of herbivores lessens browsing pressure on woody plants. More specifically, herbivores spend less time inside wolf territories which creates areas of refuge where these plants can grow unimpeded by browsing of herbivores. Growth and recruitment of these plants is important for ecosystem diversity because they provide habitat for smaller mammals and birds.

            In addition to affecting herbivore species and vegetation, wolves contribute to the ecosystem by providing food for scavenger species. They also keep mesocarnivore populations (such as coyotes) low, which protects birds and small vertebrates from overexploitation.

            The second portion of the article discusses the changes seen in the Yellowstone northern winter range since the reintroduction of wolves in 1995. Since the article was published in 2004, the data in this area is not up to date. However, at the time of the article, much change had already been affected in this ecosystem by the presence of wolves. The data presented focuses on elk and woody plants.

            In separate studies on aspen and cottonwood, both species were seen to have reduced recruitment (i.e. survival of juvenile plants to join the population) in the 1920s and 1930s, coinciding with the extirpation of wolves from the area. This reduced recruitment was found to be independent of climate or other events such as fire or floods. The National Parks Service attempted to reduce the numbers of the elk herds in order to relieve some of the browsing pressure on these plants. As a result, elk herds were reduced from between 8,000 and 11,000 in the early 1950s to between 4,000 and 8,000 in the 1960s. When these efforts ceased in 1969, elk numbers increased to between 12,000 and 18,000 from the 1970s to the 1990s. Regardless of this decrease and increase in elk numbers, woody plants were not relieved from browsing pressure until the reintroduction of wolves in the mid-1990s. Since then, increased recruitment of aspen, willow, and other woody plants has been observed, especially in areas of high predation risk for herbivores.

                                  Willow along Blacktail Creek in spring 1996 (left) and 

                                  summer 2002 (right).¹

           
            After reading this article, it seems apparent to me that wolves are an important element of their native ecosystems and that removal of wolves from these ecosystems has had a negative effect. The overall benefit of wolves to the ecosystem is to promote biodiversity by affecting prey behavior, thereby reducing browsing pressure on woody plants and allowing formation of habitats for smaller mammals and birds. In my opinion, the pros of wolf reintroduction for the environment outweigh the cons of wolf reintroduction for livestock producers. However, I maintain that the conservation community should recognize the cost of living with wolves that is paid by livestock producers, and make every effort to communicate and compromise with these producers.

1.Ripple, W.J., & Beschta, R.L. (2004). Wolves and the ecology of fear: can predation risk structure ecosystems? Bioscience, 54(8), 755-766. 

Management of Wolf-Livestock Interactions

            Building off of the issue of wolf-livestock interactions, this post will discuss the possibility of limiting wolf predation on livestock through management action. While compensation programs are an important tool to manage ranchers’ attitudes toward wolves, management plans aimed at reducing these interactions are also key in areas where wolves and livestock coexist. I recently read an article published in ­­­­Frontiers in Ecology and the Environment in 2011 detailing a study of wolf predation on cattle in Alberta, Canada¹. This study highlighted important trends seen wolf-cattle interactions in this area and suggested a management technique for reducing cattle loss to wolves.
            The study area is a predominantly ranching landscape with large range lands used seasonally for cattle grazing, similar to parts of the NRM area for wolf reintroduction in the US. Wolf diet compositions were studied year-round using scat analysis and field searches based on GPS telemetry relocations. The results showed an increase in percent biomass of cattle in wolf diets from 31% during the non-grazing season to 74% during the grazing season. The authors believe that this prey switching is due to the increased presence of cattle within the wolf territories during the grazing season as well as higher nutritional demands of wolf packs since this is the same season during which wolves are rearing pups.

            Wolves were found to scavenge more during the non-grazing season than during the grazing season, and the majority of scavenging was from the boneyards where ranchers dispose of carcasses of livestock that have died of disease or are otherwise unfit for human consumption. Because boneyards are only required to be 400 meters from facilities or residences, boneyard scavenging brings wolves dangerously close to humans and livestock. In addition, it gives wolves a taste for cattle and increases the likelihood that they will prey on livestock instead of wild ungulates.

            The management technique proposed in this paper is the use of metal storage bins for anything that may attract wolves or other carnivores, such as carcasses, grain, or garbage. The use of these bins not only decreases the chances of wolves approaching facilities or residences, but also prevents them from becoming accustomed to eating cattle due to scavenging from boneyards.

            Although this study was performed in Canada, I believe that the proposed development of management plans aimed at reducing wolf-livestock interactions also applies to areas of wolf reintroduction in the US. The area where the study was performed and the NRM area are similar in that they are both ranching landscapes that overlap wolf territories. The plan proposed in the article for use of metal storage bins to limit access to objects which might attract wolves should also be implemented in the US.

            In my opinion, further development of additional management plans is integral to the support of wolf conservation in the US. Not only will these plans reduce loss of livestock to wolves and therefore the impact of wolves on the livestock industry, they also have the potential to positively influence the attitudes of ranchers toward wolf conservation. Resources detailing the research being done and the management plans being implemented should be made available to all ranchers in the area. Compromises on the issues surrounding wolf reintroduction cannot be reached without thorough communication and cooperation between wolf conservationists and livestock producers. 

1.Morehouse, A.T., & Boyce, M.S. (2011). From venison to beef: seasonal changes in wolf diet composition in a                 livestock grazing landscape. Frontiers in Ecology and the Environment, 9(8), 440-445. 

Livestock Depredation by Wolves

            My previous post reviewed the issue of wolf reintroduction from a conservationist stand-point. A conversation with my advisor at Iowa State University the other day made me look at it from the alternate perspective of livestock owners in areas where wolves have been reintroduced. My advisor is Dr. Stephanie Hansen, a beef nutritionist; when I mentioned my blog, she told me about her experiences with this issue. Each year, Dr. Hansen takes a group of students to Yellowstone. As part of this trip, they visit with both park rangers and ranchers. Understandably these two groups have very different views of wolf conservation. Dr. Hansen mentioned that wolf predation upon livestock is a huge problem for ranchers in that area and that she has heard several stories from ranchers who have found calves or sheep killed by wolves but not eaten. Hearing these stories made me want to explore the issue of wolf-livestock interactions and I found an article which deals with various facets of that relationship.

            The article is a report on a study done on the effects of livestock depredation by wolves on the livestock industry in Idaho, Montana, and Wyoming¹. The study area contains both natural prey species for wolves as well as domestic livestock, and agricultural lands and towns as well as public reserves. Livestock depredation is primarily an issue due to the overlap between wolf range and private and public range lands used for livestock grazing.

An important issue addressed by this study is the belief that wolves kill livestock in excess of their food needs, also known as surplus killing. The authors suggest that surplus killing by wolves may occur at a higher rate for domestic animals than for the wolves’ wild prey due to the fact that artificial selection for desirable production traits has reduced the animals’ tendencies for certain anti-predator behaviors.

            This study documented attacks of wolf on sheep and cows in the three states mentioned above from 1987-2003 and analyzed the number killed per attack and the biomass consumed of each carcass. Over the entire study, 219 cows were killed by wolves in 158 attacks and 602 sheep were killed in 68 attacks. The data on biomass consumed indicate that the majority of these attacks were motivated by a need for food. However, wolves utilized a greater percentage of the carcass in attacks on cattle and killed more than they needed more often when attacking sheep than when attacking cattle. The data indicate that wolves do exhibit surplus killing on sheep but not on cattle. The authors admit that this data may be biased due to the inability to know how many wolves were involved in each individual attack.

             In addition to surplus killing, Muhly and Musiani examined the efficacy of livestock compensation programs. These programs have been utilized for more than 20 years in this area in an attempt to reduce the animosity of livestock producers toward wolves. The importance of prompt payment of compensation is highlighted, as producers need to quickly replace an animal in order to avoid further loss of profit, which is gained from growth and reproduction. Even if payment is immediate, however, these programs are further limited because they are unable to compensate for loss of important breeding animals or emotional investment.

Another element to take into account when considering the costs of wolf conservation to livestock producers is the benefit which private rangelands pose to wolves. For wolves and their prey species, these rangelands provide invaluable habitat. Current trends in livestock and land value make selling these rangelands financially attractive to many livestock producers. Due to increasing demand for natural amenities, many rangelands are being converted to rural-residential developments. The authors suggest that public funds allotted for wolf conservation may be well-put towards supporting the livestock production industry in these areas, with the goal of conserving rangelands.

This article seems to be written from a perspective which sides with wolf conservation, but is open to understanding and meeting the needs of livestock producers. I believe that if this type of attitude were more prevalent among both conservationists and livestock producers, much of the controversy and animosity surrounding wolf reintroduction could be resolved. It is clear to me that there is no answer that can satisfy everyone. Wolves pose a threat to the livelihood of livestock producers, but they also pose many benefits to the ecosystem in this area. Given that, I believe that people on both sides of this issue need to be open-minded and seek to fully understand the opposing perspective. If this can be achieved, a compromise could be reached.

When reading the results section of this article, I thought back to what Dr. Hansen had told me of her interactions with livestock producers who deal with wolf predation. It seems to me that several of them would have reason to disagree with the authors’ conclusion that surplus killing of cattle by wolves is not common. I think part of the compromise that needs to occur is for scientific-minded conservationists to understand that livestock producers who lose cattle to wolves will not necessarily allow their opinion of wolves to be swayed by purely scientific conclusions such as those presented in this article.

Compensation programs, as described in this article, seem to be a good start toward finding a compromise between livestock owners and wolf conservationists. However, I agree with the authors’ recommendation that compensation payments must be as prompt as possible in order to be meaningful within the economic context of the livestock industry. Another part of the necessary compromise is that compensation agencies should strive to understand the livestock industry in order to be on the same page as their payees. Also, the livestock producers should accept that compensation is not a perfect answer and it is unrealistic to expect compensation to cover every aspect of the lost animal, such as emotional investment.

Livestock-wolf interactions are a huge part of the controversy surrounding wolf reintroduction. This article is a solid foundation for understanding those interactions and what steps need to be taken to resolve animosity between conservationists and livestock producers.

1.Muhly, T.B., & Musiani, M. (2009). Livestock depredation by wolves and the ranching economy in the Northwestern   U.S. Ecological Economics, 68(8), 2439-2450. 

Overview of Gray Wolf Reintroduction

            This blog will explore the issue of the reintroduction of the gray wolf (Canis lupus) to North America. I am starting out with a very minimal knowledge of the issue, so this first post will summarize the chapter concerning wolves from Cristina Eisenberg’s book, The Carnivore Way: Coexisting with and Conserving North America’s Predators¹. My summary will primarily focus on the history and current state of wolves in the United States.

            Three subspecies of gray wolves were found in North America originally: the Mexican gray wolf in the southern US and Mexico, the plains wolf, and the timber wolf in the northern US and Canada. Beginning in the 1880s until the 1970s, a policy of predator control led to the near extermination of wolves throughout the United States. In 1974, the Mexican gray wolf and the timber wolf were listed as endangered species by the Endangered Species Act (ESA); the plains wolf had become extinct in 1926. Two areas were designated for wolf reintroduction: the Northern Rocky Mountain Recovery Area (NRM), which included Montana, Wyoming, Idaho, and parts of Oregon and Washington, and the Blue Range Wolf Recovery Area (BRWRA), which included parts of New Mexico and Arizona. Since the plains wolf had become extinct by that time, the timber wolf was to be reintroduced in the NRM area and the Mexican gray wolf into the BRWRA area.

            Reintroduction of the timber wolf has been very successful. 66 wolves were captured in Canada and released into Yellowstone National Park and Idaho in 1995-96. The NRM population grew quickly and reached recovery goals (300 wolves and 30 breeding pairs) by 2002. The United States Fish and Wildlife Service (USFWS) proposed to delist NRM wolves from the ESA in 2007; in order to do so, it needed to first approve wolf management plans from the states of Montana, Wyoming, and Idaho. A lawsuit was filed following this proposal and the court ruled that the USFWS had irresponsibly approved a sub-par wolf management plan from Wyoming. Later that year, the USFWS again proposed to delist NRM wolves, excluding those in Wyoming. It was refused because, under the ESA, a recovery area could not be delisted in parts but only as a whole. In 2011, a rider was added to an unrelated bill which delisted the entire NRM, regardless of the 2009 ruling; wolves have been hunted in all three states since.

            In the BRWRA, wolf reintroduction has not been as successful. The Mexican gray wolf had neared extinction in the wild and only 5 wolves were able to be captured. Several other captive wolves were certified as pure Mexican gray wolves and a breeding program was begun in 1977. In 1998, eleven wolves were released. Over the years, more captive-bred wolves have been released at various times to keep a stable population. Challenges that face the BRWRA wolf population include poaching, legal killing, and a smaller average litter size than that of NRM wolves. Legal killing of these wolves occurs under Section 10(j) of the Endangered Species Act, which allows removal of wolves which threaten humans and/or livestock. The BRWRA population was only 75 in 2012.

            In this chapter, Eisenberg also discusses the effect of wolves on local ecosystems and why reintroduction is important. The threat of predation effects the feeding habits of the wolves’ ungulate prey, which in turn effects the plants. In Yellowstone, for example, dense elk populations before reintroduction caused heavy browsing of woody plants such as aspens. With the reintroduction of wolves, the elk have changed their habits to become less stationary and more migratory and the aspens and shrubs have been able to grow taller and healthier. In turn, these plants are now able to offer habitats for other species.

            Despite the success of the NRM reintroduction, the future of wolves in this area is uncertain. Following the removal of ESA protection, 37% of the wolf population in Montana and Idaho was killed due to both legal and illegal hunting. Eisenberg points out that hunting of wolves may have large effect on their long-term population stability. Hunting disrupts the wolves’ pack structures; these packs may then split, resulting in much smaller packs made up of younger individuals. These younger packs are more likely to approach humans or hunt livestock rather than elk. In addition to disrupting the long-term viability of the wolf population, wolf hunting may have negative consequences for people as well. Since 2009, hunting has greatly reduced wolf viewability within Yellowstone. This in turn has caused a decline in tourism, which many small towns near the park rely on.

            Now that I have become familiar with the current state of wolves in North America, I plan to explore the issue more in depth with future posts.      

           

1. Eisenberg, Dr. Cristina. (2014). The carnivore way: Coexisting with and conserving North America’s predators.             Washington, D.C.: Island Press.