The reintroduction of wolves to Yellowstone National Park turned the nation’s most prominent national park into a laboratory of sorts, whereby scientists could document and measure the effect of wolves on a variety of other species. Since their return, dozens of studies have been published purporting to show some effect of wolves on some other component of the Yellowstone ecosystem. These studies, and associated work in the popular news media, have credited wolves with a variety of effects, most prominently, the regeneration of willow and aspen (e.g., Ripple & Beschta 2006, 2007). In a recent (June, 2012) article published in the journal, Biological Conservation, Mech (link) pointed out that most of the so-called “effects” of wolves reported in the popular media were based upon correlative evidence and, perhaps more importantly, the validity of many of these claims are being challenged by emerging science (Mech 2012). He went on to accuse scientists and the popular news media of “sanctifying the wolf” by disproportionately covering the positive impacts (or benefits) of wolves.
On the “effects” of wolves
Mech provides several examples where recent evidence conflicts with initial studies that documented some effect of wolves. So, for example, Mech notes that a number of studies have found that wolves tend to reduce coyote populations (see Ballard et al. 2003); however, while just such an effect was initially documented in parts of Yellowstone, coyote populations have since rebounded, returning to pre-wolf levels. More prominently, Mech notes that despite the claims of some researchers that wolves have caused a “trophic cascade”–i.e., increasing willow and aspen by reducing the number of elk in the Northern Range herd and changing elk foraging behavior–there is still no consensus on the cause of elk decline in this area (Vucetich et al. 2005, for example, argued that hunter harvest was primarily responsible for the decline and elk) and new evidence suggests elk are not modifying the behavior in the presence of wolves (e.g., Kauffman et al. 2010).
Are scientists and the news media “sanctifying” the wolf?
Mech’s primary point is a good one. Specifically, people should not take as gospel the correlative studies that have thus far been published regarding wolves’ beneficial effects. What scientists don’t know about wolves’ effects on Yellowstone is still vast relative to what we think we have sorted out. And determining how they effect species in more heavily managed areas (e.g. national forests) will (no doubt) be even more challenging (Mech 2012). However, Mech loses loses me when he accuses scientists and the news media of “sanctifying the wolf”:
“But what explains the rash of recent research purporting to show beneficial effects of wolves beyond releasing vegetation? With wolf lay advocates it is just natural to want to promote their favorite animal and to try to counter the known negative effects of wolves and the claims fostered by people who vilify wolves, an increasing lot as wolves recover and proliferate. Thus wolf advocates eagerly seize on any study they consider favorable to wolves. The media become complicit by immediately publicizing such studies (Table 1) because of the controversial nature of the wolf. And all this publicity reverberates on the internet. Seldom, however, do studies contradicting the sensational early results receive similar publicity” (Mech 2012, p. 146).
Certainly, there is little doubt that some advocates of wolves would “sanctify” the wolf by reporting only those effects deemed beneficial. Mech is on solid ground there. However, Mech’s fundamental claim is that the news media (and science) is biased in favor of the wolf. Mech contends, for example, that “few recent studies have been published and popularized about what the public might consider negative about wolves”. Here, the empirical evidence does not support Mech’s view. While Mech relies on 11 purposively selected news articles as evidence of bias, Houston et al. (2010) recently reviewed more than 6,000 articles–totaling almost 30,000 paragraphs of text. In contrast to Mech’s claims, they noted that more than 70% of the paragraphs coded over a ten-year time period portrayed wolves negatively. Moreover, they found that while 2.3% of the paragraphs they coded concerned wolves’ beneficial impacts on ecosystems, the exact same proportion (i.e. 2.3%) discussed their negative impacts on ecosystems. Finally, they found that 30.5% of the paragraphs discussed wolves’ negative impact on human activities, whereas only 2% claimed a positive impact on human activities. The evidence here is quite clear–there is no indication that the news media is biased in favor of wolves; indeed, the evidence points strongly in the other direction.
Mech’s primary point–that correlative evidence is insufficient for establishing causation–is important, and I hope it does not get lost here. Despite decades of research, we know very little about wolves and their effects on ecosystems. However, for every story that claims some benefit of wolves on ecosystems, there are an equal number that claim some negative impact–some cost. And what we know about the costs of wolves is just as uncertain as what we know about the benefits.
UPDATE: See Dr. Mech’s reply
Literature Cited
Ballard, W.B., Carbyn, L.N., Smith, D.W., 2003. Wolf interactions with non-prey. In: Mech, L.D., Boitani, L. (Eds.), Wolves: Behavior, Ecology and Conservation. University of Chicago Press, pp. 259–271.
Houston, M., Bruskotter, J.T. & Fan, D., 2010. Attitudes Toward Wolves in the United States and Canada: A Content Analysis of the Print News Media, 1999–2008. Human Dimensions of Wildlife 15(5), 389-403.
Kauffman, M.J., Brodie, J.F., Jules, E.S., 2010. Are wolves saving Yellowstone’s aspen? A landscape-level test of a behaviorally mediated trophic cascade. Ecology 91, 2742–2755.
Mech, L.D., 2012. Is science in danger of sanctifying the wolf? Biol. Conserv. 150, 143-149.
Ripple, W.J., Beschta, R.L., 2006. Linking wolves to willow via risk-sensitive foraging by ungulates in the Northern Yellowstone ecosystem. Forest Ecol. Manage. 230, 96–106.
Ripple, W.J., Beschta, R.L., 2007. Restoring Yellowstone’s aspen with wolves. Biol. Conserv. 138, 514–519.
Vucetich, J.A., Smith, D.W., Stahler, D.R., 2005. Influence of harvest, climate, and wolf predation on Yellowstone elk, 1961–2004. Oikos 111, 259–270.
