By: Devi Gopal
There is a heated debate about when humans should interfere with ecosystems. The general consensus is when the health of an ecosystem begins to decline in the form of population loss or vegetative destruction, humans will take it upon themselves to find the source of the problem and try to fix it. It can be a difficult decision as there is always the chance that we will accidentally inflict further damage by disrupting the natural tendency of nature to restore itself. A recent example that highlights this difficulty is that of the wild grey wolf (Canis lupus) in Yellowstone National Park, a park that stretches across Wyoming and extends into Montana and Idaho.
These wolves were deliberately killed and virtually nonexistent by 1926 as ordered by the Federal government and state predator control efforts because it was believed that their predatory behavior was negative to the environment1. After their extirpation, there were occasionally one or two wild wolves that would migrate to Wyoming, but there was no evidence that these lone wolves had any significant impact on the environment1. The following decades revealed a new understanding of large predators and their role in healthy ecosystems. While this learning curve ultimately culminated in the reintroduction of the grey wolf, were we right to engage in such scientifically risky behavior?
What happened after the wolves were gone and the elk came out to play?
After the dismissal of the grey wolves, some ungulate species were considered to be overabundant in population size2. This was especially true for the Yellowstone elk (Cervus elaphus).
Elk populations soon began treading the line of carrying capacity, a term used to describe the maximum population an environment can sustain in terms of food and habitat2. Not only was their population size different, but their spatial dynamic also changed keeping them relatively immobile in winter months, as they had no wolf predators to fear that would otherwise keep them on the move. This change in mobility gave elk more time to browse willow, which was an unfortunate circumstance for the Yellowstone beavers (Castor canadensis) that compete for willow plants as a main food source during the winter season2.
The obvious resolution to the survival difficulties beavers were facing seemed to be reducing the population size of elk, but how to do this was the question. Field shooting and trapping became the answer in spite of the controversy surrounding this approach. Although the elk population was reduced by 75% by the 1960s, there was a callback on this mode of reduction in an attempt to reduce human intervention and rely on natural regulation of this species instead3. It was not until 1995 that a decision was made to reintroduce the grey wolf to the Yellowstone area3. Before the reintroduction, several studies attempted to predict the future impacts of wolves on the Yellowstone ecosystem. All models assumed that elk would be the primary prey for the wolves, but elk population was only predicted to decline 5% to 30%, with levels dependent on the extent of hunting outside of Yellowstone3. Suggestions were also made that some reduction in the number of female elk killed by hunters outside the park would be necessary to reduce populations to an adequate level and restore ecosystem balance for the vegetation and the beavers3.
After the wolves were back and the elk escaped in fear…
The reintroduction of wolves has pioneered tabloids that describe the intervention of our hand as having only been positive for the Yellowstone ecosystem. The truth has proven to be a tad more complex as the cascading effects of this reintroduction is not fully understood. The highlights are that the willow plant does indeed now thrive along streams (although still patchy in other areas) attracting songbirds for habitat purposes. Beavers no longer have to worry about the lack of willow during the winter and have been able to reemerge, spread and build new dams and ponds cascading the emergence of new types of fish2. The confusion emerges when we attempt to grasp why wolves specifically had such an immense impact on this ecosystem despite the black bears, grizzly bears, cougars, and coyotes that continued to consume elk prior to the wolf reintroduction.
One theory to consider is Foraging Theory, which predicts that animals will sacrifice feeding effort to reduce a predation risk by increasing time spent vigilant, i.e. periodically pausing feeding to cautiously look around, or by decreasing feeding time to stay on the move4. Perhaps it can be reasonably hypothesized that the addition of a predator put elk over the edge of concern for their survival, which catalyzed the observed increase in elk mobility, and the resulting reduction in consumed willow. If this is the case, then we have to review the question of whether there will there be a plateau for where elk and willow populations stabilize as part of a newfound ecosystem balance for Yellowstone. If no plateau is met, then human intervention will have done nothing but changed the dynamic for how the Yellowstone ecosystem remains unbalanced by human terms.
While the case of the grey wolf has so far been a positive one that scientists continue to study as a model for understanding the predator-prey dynamic and how this functions to shift ecosystems, it was also risky4. It is true that there was extensive modeling and intensive discussions before the decision to make this reintroduction was made, but there was no accurate way to 100% know what the effects would be and continue to be. It becomes a matter of having faith in the numbers, namely probabilities and likelihoods that mathematical models produce and we use to extrapolate seemingly reasonable conclusions and decisions. So when we return to the question of whether we were right to engage in such scientifically risky behavior, we come to an impasse. All we can do is cautiously agree that our guess and check mode for ecological preservation will hopefully provide a “dos and don’ts” list that we will use to moderate future human intervention.
- The Wildlife News,. ‘History Of The Greater Yellowstone Wolf Restoration’. N.p., 2006. Web. 9 Dec. 2014.
- Yellowstone Park,. ‘Wolf Reintroduction Changes Ecosystem’. N.p., 2011. Web. 9 Dec. 2014.
- Smith, D. W., et al. (2003). “Yellowstone after Wolves.” BioScience 53(4): 330-340.
- Laundr, J. W., et al. (2001). “Wolves, elk, and bison: Reestablishing the “landscape of fear” in Yellowstone National Park, U.S.A.” Canadian Journal of Zoology 79(8): 1401-1409.