The relationship between the Yellowstone Ecosystem and its reintroduced wolves may be more complicated than just a “trophic cascade.” ©Candice Gaukel Andrews
In ecological circles, a trophic cascade is a term used to describe a process in an ecosystem that starts at the top of the food chain and works its way down to the bottom. The classic example often given of a trophic cascade is what happened in Yellowstone National Park when wolves were reintroduced in 1995.
In the video below, which was produced by Sustainable Man, a website dedicated to sustainable lifestyles, this quintessential illustration of a trophic cascade is discussed.
Recently, however, some, such as Arthur Middleton, a postdoctoral fellow at the Yale School of Forestry and Environmental Studies, are challenging the way that we have thought about the wolves’ role in Yellowstone since the mid 1990s. Writing in “The Opinion Pages” of The New York Times, Middleton states that the reintroduction of wolves to Yellowstone is far more complicated and nuanced than can be explained by a trophic cascade. He argues that:
“The strongest explanation for why the wolves have made less of a difference [in Yellowstone National Park] than we expected comes from a long-term, experimental study by a research group at Colorado State University. This study, which focused on willows, showed that the decades without wolves changed Yellowstone too much to undo. After humans exterminated wolves nearly a century ago, elk grew so abundant that they all but eliminated willow shrubs. Without willows to eat, beavers declined. Without beaver dams, fast-flowing streams cut deeper into the terrain. The water table dropped below the reach of willow roots. Now it’s too late for even high levels of wolf predation to restore the willows.
Conserving large carnivores—such as wolves in Yellowstone National Park—is crucial not just for ecological reasons, but for ethical ones, too. The reintroduction of wolves to Yellowstone has stimulated waning American interest in ecosystem and wildlife conservation.
“A few small patches of Yellowstone’s trees do appear to have benefited from elk declines, but wolves are not the only cause of those declines. Human hunting, growing bear numbers, and severe drought have also reduced elk populations. It even appears that the loss of cutthroat trout as a food source has driven grizzly bears to kill more elk calves. Amid this clutter of ecology, there is not a clear link from wolves to plants, songbirds and beavers.
“Still, the story persists. Which brings up the question: Does it actually matter if it’s not true? After all, it has bolstered the case for conserving large carnivores in Yellowstone and elsewhere, which is important not just for ecological reasons, but for ethical ones, too. It has stimulated a flagging American interest in wildlife and ecosystem conservation. Next to these benefits, the story can seem only a fib. Besides, large carnivores clearly do cause trophic cascades in other places.
In the end, Yellowstone benefits from its large carnivores—even if a link from wolves to plants to songbirds to beavers cannot be traced. ©Candice Gaukel Andrews
“But by insisting that wolves fixed a broken Yellowstone, we distract attention from the area’s many other important conservation challenges. The warmest temperatures in six thousand years are changing forests and grasslands. Fungus and beetle infestations are causing the decline of whitebark pine. Natural gas drilling is affecting the winter ranges of migratory wildlife. To protect cattle from disease, our government agencies still kill many bison that migrate out of the park in search of food. And invasive lake trout may be wreaking more havoc on the ecosystem than was ever caused by the loss of wolves.
“When we tell the wolf story, we get the Yellowstone story wrong.”
Watch the video below, then let me know what you think. Are wolves truly the agents of a trophic cascade in Yellowstone? Or if that’s a myth, by perpetuating it, are we taking attention away from the very real conservation threats to that ecosystem?
Here’s to finding your true places and natural habitats,
Candy
I loved this video and how pretty the wolves.
Introduce snow leaopard also for more conservation.
I’ve seen this vid before, and while some may question the veracity of its claims and the causal effects illustrated, we (IMHO) must all recognize the interconnectedness/interdependence of all species. Not one–from the top predator to the lowliest prey species–can exist without the other (at least for long).
amazing
Wonderful! I really enjoyed this video.
As far as I see it we need our apex predators at the top of the chain and all the others below to maintain a healthy eco system. Humans are a part of the ecosystem but they need to live in balance with the other parts of the system. We interfered here and we need to allow much more time before we can properly decide whether the reintroduction of wolves has helped Nature to repair the damage to the eco system in Yellowstone.
The idea that Yellowstone’s ecology is too broken to be fixed by one species or restoration method is sound logic. My problem with the video is that it ignores other changes in the management of Yellowstone over the past four decades. We have gradually progressed from micro-management populations at the turn of the century to natural regulation for many species. Maybe there are other forces (or a combo of forces) at work here than just wolves? The video was a lovely promotion for the park and for hands-free conservation in general, a beautiful example of the “butterfly effect”. But I am with Mr. Middleton; not enough evidence to support the wolves as the lone super heroes in this story. Overstated trophic cascade is possibly detracting from other challenges our natural areas will face in the warmed-up future.
Interesting theory. I wonder why no mention has been made of the Yellowstone fires and the changes to the ecosystem shortly before the wolf reintroduction.
Data is to be had for the success of the wolf reintroduction program. My question is how much data, over how much time, is needed to confirm the video claims? The unique geography, weather and how many other things are part of it? It was a cool video regardless.
I agree with Anna. Without the mention of the scientists and the work to show how things have changed, it could appear to people who are in opposition can argue that it is hokum. The piece is beautifully done and articulated well, but it needs evidence to show the change.
I think the important point in this situation is the fact that the film maker used an iconic species to highlight the complexity of ecological systems by telling the wolf story.
Film makers are always faced with the dilemma that you can never cover every fine detail of the story, because you tend to loose the viewer’s attention.
It was a good documentary. Look how it made us think and discuss the issues that were not mentioned.
I think this is wonderfully done, but I wish that the sources of the science were cited. As is, the film comes across as ‘simply true’, which nothing ever is- someone figured out these connections and (hopefully) measured them and subjected them to peer review. Steve and Chris Agnos are wonderful artists but they aren’t scientists.
While this is a beautiful video it does what so often happens by simplifying a tremendously complex system down to the role of wolves. Significant impact to be sure. Yet, other forces are at work. There is too little area saved from human interference and too little long-term ecological research underway. One exception is our Cedar Creek Natural History Area. It was established in the 1930’s and has resulted in some remarkable studies on what happens over the long term. These studies include pioneering work on energy flow and David Tillman’s more recent efforts to discern what limits growth and extinction. Cedar Ck is owned and managed by the University of MN.
If one reached its climax ecosystem-biotic and abiotic factors dependent-certainly, there is an ecological interaction in scenario. I believe predators have important role in the process of succession, obviously, with the help of other species as well. I-particularly-evaluate the quality of a stretch of Woods by the number of dead animals that I can identify, either directly or indirectly. The more predation exist, richer is the ecosystem. It’s not a specific predation, but is rather varied, involving different Zoological orders. The more bodies there are, the more lives we will have.
Eliminating a species- carnivore or not- is going to upset the ecological system (balance). Which it did in Yellowstone. Steps taken to restore that balance are steps in the right direction. I do not see evidence that the wolves have done harm. I believe that they are generating tourist revenue for the Park. The trophic cascade is regenerating and for that we can be grateful. Our job is not done- but the wolves are not to blame.
Conservation issues vie for space among some really preposterous ad campaigns on TV. To get a “web of life” themed documentary to go viral in today’s media scene is a wonderful achievement.
Absolutelyy – yes! Nature knows best.
Hello; God did create a perfect living planet which functioned beautifully before humankind emerged. Maybe we, as a species, are finally stating to learn how to assist Mother Nature in maintaining the Garden we all occupy as temporary tenants. Hopefully this Yellowstone revelation ideal will expand, by example, to the rest of humankind and our entire biosphere (I’m forever an optimist ! :)). Hope springs eternal!
I am amazed!
Candice, thank you framing this discussion in an open and debatable manor. The thing that stuck out the most for me was the question, “Does it actually matter if it is true?”, referring to whether the reintroduction of wolves in Yellowstone caused all of the biological changes. Without delving into any discussions of the validity of the claims, it matters very much that it is proven to be true. In the absence of truth, we are being deceived. Deceit leads to distrust, and results in the loss of the audience which one is trying to reach to support a cause. I will leave it to others to discuss point-by-point the validity of the claims made in the video.
I don’t think it is either, or. The wolves no doubt have some effect (would have even more if they weren’t being shot when they leave the Park for a short time) but I am sure there are other factors at work too. Nature is vastly complex and we humans are not yet able to fully understand what is going on. Keep up the research!
I assume somewhere there is a bunch of peer reviewed papers to support the claims….. Maybe I’m being naive.
Really illustrates well the shortcoming of Cartesian-style cause-effect thinking and how much more appropriate to think in terms of systems or constellations. Thanks for sharing the video!
Thanks for explaining how complex could be to understand interconnection of our ecosystem. Sustainable development is really about managing this complexity and getting always a deeper holistic knowledge.
In his NY Times editorial, Middleton mentions two studies that support his view but fails to include the long term work done within the Park by Doug Smith nor the years of work done by Ripple and Beschta, among others. I have an entire book filled with studies that confirm how apex predators are key in balanced habitats. As for the elk in Yellowstone that Middleton uses as examples, yes, there may be some elk who still do not fear wolves but not enough time has passed nor are wolf populations yet large enough for the huge elk population to even begin to know this predator. Remember, several generations of elk have lived in the Rocky Mountain region without wolves. Fear is not just instinctive. In fact, it really is more a learned behavior. I see it here in New York State with White-tailed Deer. In the city where they flourish and are not hunted, I’ve come across many who show no fear of humans. I’ve got within 15 feet of them with a group of 10 students. Yet on my property in a high hunting area, the deer run if they even see me move about in my garden 100 feet away. This is a sketchy and incompletely researched opinion piece.