Ever Hear of These? « Arthur Morris/BIRDS AS ART

Ever Hear of These?


Woke way too early. Way. Took an early swim. Finished the last two exhibit categories by phone with denise. Many thanks for your help Lady D. My NY Football Giants won again, largely due to the total ineptitude of the Buffalo Bills. Then an ice bath followed by more football.

This blog post should be published automatically at 5:30 am on Monday, October 5.

Thanks to Chip Jackson

Thanks to my accountant, Chip Jackson, not only for the great job that he did getting me prepared for my audit, but for sending a link to an amazing video entitled, “How Wolves Change Rivers.” I had never heard of a trophic cascade, and I am betting that most of you have not either.

Here is the must-watch video: How Wolves Change Rivers.

Ever Here of These?

What are Trophic Cascades?

Trophic (pronounced with the long oh sound) cascades occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation. That in turn affects lower trophic levels. The video takes a look at what has happened in Yellowstone National Park when the top predators, in this case wolves, are successfully reintroduced into an ecosystem. The results seem to have been astounding. Aldo Leopold is generally credited with first describing the mechanism of a trophic cascade, based on his observations of overgrazing of mountain slopes by deer after human extermination of wolves….

I urge everyone to click here and watch the 4 minute, 33 second video. I have watched it several times and you will probably wind up doing the same thing. The quality of the video clips is pretty much so-so but the narration by George Monbiot is first rate: the guy gas a great voice. But it is the message that steals the show….

The video appears to have been done under the auspices of an organization named Sustainable Man. I did some web surfing and wound up at the Sustainable Human website here. It has the same logo that appears at beginning of the video but then things get a bit mysterious. The website is quite interesting. If I am understanding correctly the guy running it and the blog is the son of a former mayor of San Francisco, Art Agnos. I could not find any connection to or mention of the “How Wolves Change Rivers” video. Christopher James Herman Agnos’s Life Resume, is however, quite an interesting read. You can find it here.

I searched around a bit more on the web and found some interesting stuff on Wikipedia here. The entry there includes this:

The gray wolf, after being extirpated in the 1920s and absent for 70 years, was reintroduced to the Park in 1995 and 1996. Since then a three-tiered trophic cascade has been reestablished involving wolves, elk (Cervus elaphus), and woody browse species such as aspen (Populus tremuloides), cottonwoods (Populus spp.), and willows (Salix spp.). Mechanisms likely include actual wolf predation of elk, which reduces their numbers, and the threat of predation, which alters elk behavior and feeding habits, resulting in these plant species being released from intensive browsing pressure. Subsequently, their survival and recruitment rates have significantly increased in some places within Yellowstone’s northern range. This effect is particularly noted among the range’s riparian plant communities, with upland communities only recently beginning to show similar signs of recovery. See the video!

The WyoFile site here included this useful material in an excellent article by Deb Donahue:

The scientific evidence is that ecosystems unravel when wolves and other “keystone” predators are removed.

The term for this phenomenon is a “trophic cascade,” defined as the “progression of indirect effects [caused] by predators across successively lower trophic levels.” (Estes et al., Encyclopedia of Biodiversity, 2001). “Trophic” is defined as “the food relationship of different organisms in a food chain.”

Trophic cascade theory can be traced to Aldo Leopold’s observations more than 60 years ago in the Southwest:

I have lived to see state after state extirpate its wolves. I have watched the face of many a new wolfless mountain, and seen the south-facing slopes wrinkle with a maze of new deer trails. I have seen every edible bush and seedling browsed, first to anemic desuetude, and then to death. I have seen every edible tree defoliated to the height of a saddle horn. (A Sand County Almanac 1949)

A consensus is growing: “Questions about trophic cascades have shifted from whether to when, where and how often.” (Pace et al. 1999). There is “increasing evidence that the absence of large carnivores can initiate cascading perturbations through the trophic webs.” (Soulé and Terborgh, 1999:). In the past ten years, field studies supporting this conclusion have appeared in leading journals and been reported by the National Research Council.

Trophic cascades involving wolves or cougars have now been demonstrated in national parks in five different North American ecosystems – Yellowstone, Yosemite, Wind Cave, Jasper (in Alberta), and Zion. Similar findings from Olympic National Park will be published later this summer.

In each study area the long absence of wolves or cougars resulted in a similar “cascade” of effects:

• Large herbivores, such as elk or deer, increased in number and foraging behavior changed significantly.
• These animals over-browsed preferred plants, especially deciduous trees and shrubs like cottonwood, aspen, willow, and oaks, and spent more time in riparian areas.
• As a consequence, “recruitment” of cottonwood and aspen (i.e., the growth of seedling/sprouts into tall saplings and trees) was drastically reduced, and uncommon plants became rare or were disappeared completely.
• Long-term loss of streamside vegetation caused major changes in channel morphology and floodplain function.
• Loss of berry-producing shrubs, and young aspens and cottonwoods, led to changes in the diversity and abundance – and sometimes the outright loss – of other species, including beaver, amphibians, and songbirds.
• The disappearance of top predators triggered an explosion of smaller “mesopredators,” such as coyotes, which led to further cascading effects.

Make the blog interactive and teach me something…

If you get half as interested in learning about trophic cascades as I did, please feel free to share any insights. Please also let us know if you think that there any exaggerations in the video…


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14 comments to Ever Hear of These?

  • Very, very interesting and an excellent example of the unintended consequences humans unleash when they meddle (even in seemingly minor ways) in the affairs of Mother Nature.

  • avatar Rick

    What an excellent – and quite different – blog! We learn time and again that when man interferes with nature, the results can be catastrophic. Ask the Australians about their attempts to fine tune nature and the unforeseen consequences. It was interesting to read this morning’s reports on the wild life around Chernobyl, which is flourishing despite possible radiation threats, but in the absence of mankind.

  • avatar Henry

    In all things in nature there is a balance. Powerful video exemplifying that premise. A reminder that us humans should tread carefully as far as the balance of nature is concerned. And a good reminder that predators are necessary in nature’s grand scheme for the health of an ecosystem. In nature it is what it is for a reason.

  • avatar Mark Macomber

    Excellent blog. Video on trophic cascades was very helpful in better understanding its widespread effects on ecosystems. Thanks for a clear lesson on such an important subject.

  • You might be interested in Googling Bill Ripple at Oregon State University who did much of the early studies in Yellowstone that helped justify the wolf reintroduction. There is a short two minute video with this article. http://www.opb.org/news/article/researchers-say-wolves-help-plants-by-eating-deer-/ I remember seeing a longer version that this video was taken from, but can’t put my finger on it yet.

  • Hi Artie,
    Wildlife biologists have a saying ‘You can only put two gallons in a two gallon bucket.’ For example, this means that only a specific number of fruit flies can live in a jar with an apple. It can be expanded to say that only so many deer can survive on the resources in a forest preserve or expanded even farther to say that some large number of people could consume the resources on a planet.

    Each area of land has a specific ‘carrying capacity’ for each type of animal. If an animal population starts to exceed the limit, some kind of damage will occur to the ecosystem or the animal population. Ecosystem damage is not linear. It is a web, so when one link is harmed, many others are influenced. As seen in the video, overgrazing by deer and elk cascaded to harm many other species. Harm to the over abundant animal population is usually through starvation and disease outbreaks.

    Many forest preserves in the eastern U.S. have a deer carrying capacity problem. I have seen many examples of deer consuming all of the native green plant material below about four feet off the ground. These preserves have no predators, including hunters or automobiles to keep the deer population at a sustainable level. One consequence is that the deer begin to starve and need to move out of the preserve boundaries to feed on urban landscaping, putting people at risk of injury and death from car accidents with the deer. In preserves with flowing water or steep slopes, erosion is a problem, due to lack of vegetation. In areas where there is no low growing vegetation, there are no ground nesting birds and few small mammals. When small test plots in the preserves are fenced in, the vegetation comes back, but some plant species are very slow in recovering.

    Another interaction in this ecosystem web is that the deer often do not eat non-native invasive plants, such as honeysuckle, buckthorn and garlic mustard. These three plant species are taking over many eastern forest preserves. They prevent sunlight from reaching the forest floor. This prevents native tree seedlings and stops growth of shorter native plants. Few native insects feed on invasive plants. Even though the forest preserve looks green to the uninformed observer, the non-native invasive plants are not feeding the deer; not feeding the insects; which in turn means not feeding insect eating birds; and finally, native plant species are being eliminated.

    Deer hunting in these preserves can bring the population under control, but much ecosystem damage has been done. The non-native plants have to be eliminated and in many cases native plant species have to be reseeded. It would be very difficult to bring large predators back into the eastern U.S. to reduce the deer population, but it would certainly help the native insects and birds if we did.

  • avatar Ted Willcox

    When we try to pick out anything by itself, we find it hitched to everything else in the universe. John Muir

  • avatar Ron May

    It never ceases to amaze me how things are “connected” in nature. Artie, thanks for jogging my memory on this topic. I do believe that there was a PBS/Nature special a few years ago that covered aspects of this “trophic cascade”. I am not sure if that is what they called it, but I do remember watching something that had the theme of how the wolf re-introduction to Yellowstone had benefits that were extremely far reaching.

  • avatar David Policansky

    Hi, Artie. I was the project director for a study the National Academy of Sciences did on Yellowstone’s Northern Range. We did the study not long after the wolves had been re-introduced and one of my contributions was to ask the committee what they thought would happen as a result of that introduction. I don’t think anybody foresaw just how big the effects would be, but the report does say that wolves could change the ecosystem quite substantially, mainly by their effects on the behavior of elk. I think Doug West is quite incorrect in attributing all the changes to the devastating 1988 fires; we could see changes happening as we watched in 2000-2002 (for example, coyotes almost disappeared and we saw coyotes that had been killed by wolves). If anyone wants to read the report it’s available here: http://www.nap.edu/read/10328/chapter/1

  • avatar Lou Kaufman

    Hi Artie,

    Thanks for the link to the video. Very powerful.


  • I think his biggest exaggeration is that wolves are responsible for all of this. He fails to mention the Yellowstone fire of 1988.Bye bye wildlife. It took years for vegetation, plants, etc. to grow back. So of course wildlife would also take its time to repopulate the area. He’s just picking wolves cause it just happens to fall into his timeline.