I always wondered why the Virgin River looked so oddly entrenched and actively eroding in Zion NP. It may be an indirect effect of the loss of the cougar. As any visitor will attest, the deer are everywhere.
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Dr. Ralph Maughan is professor emeritus of political science at Idaho State University. He was a Western Watersheds Project Board Member off and on for many years, and was also its President for several years. For a long time he produced Ralph Maughan’s Wolf Report. He was a founder of the Greater Yellowstone Coalition. He and Jackie Johnson Maughan wrote three editions of “Hiking Idaho.” He also wrote “Beyond the Tetons” and “Backpacking Wyoming’s Teton and Washakie Wilderness.” He created and is the administrator of The Wildlife News.
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This study is profoundly important: the authors have shown that pumas are important in ecosystem regulation as wolves are in Yellowstone.
That said, I still think that the top-down vs. bottom-up argument is not settled. Bottom up effects are important when there’s a drought on, for example. So scientists will continue to bicker over this for decades. The answer is: it’s both but it depends.
Another important effect that the paper discusses is vehicular traffic and pumas. More traffic, less pumas. That argues for closing roads.
And the loss of the carnivore is a big factor in the deer herd’s growth, no doubt. One need look no further than many states in the East (including Pennsylvania) to see what happened to regional deer populations when the only predator was reduced to one – the human hunter. A good overview: http://www.ecosysmp.com/testimony.html
Just insert “cougar” for “wolves” in the following quote from Aldo Leopold:
“I now suspect that just as a deer herd lives in mortal fear of its wolves, so does a mountain live in mortal fear of its deer. And perhaps with better cause, for while a buck pulled down by wolves can be replaced in two or three years, a range pulled down by too many deer may fail of replacement in as many decades. So also with cows.” (Sand County Almanac, p. 140)
Cougars are very adaptable. I am surprised that they don’t spend more time in Zion valley despite the sheer number of people. Deer that abundant have to be tempting and cougars come close to people in Cali. I am sure some (one) will eventually show up and then people will get unnerved about them (it) too close.
Hey! I didn’t know you’d put your wildlife news into blog format (I interviewed you for a JYI article on wolf reintroduction in summer of 2005).
I think that one possible aspect of why ungulate populations often explode in the absence of big predators may be because the absence of predators allow deer to create/maintain more habitat for themselves.
As many people have said, one of the biggest effects of predators on ungulates is behavioral; elk and deer can’t afford to hang out in the open anymore, thus allowing more vegetation to regenerate in valleys and river bottoms. In the East, white-tailed deer are far more numerous now than they were in pre-Columbian times. Old growth forests are not prime deer habitat; white-tails prefer edge habitat between (and including) meadows and disturbed second-growth forest. In centuries gone by, meadows were rare in most of the East. They were probably very important places for deer, like today, but when wolves and cougars patrolled the region, deer probably could not afford to remain out in the open long. With predators gone, deer can spend much more time in open places…and expand them. Constant grazing excludes saplings from colonizing open spaces and favors rapidly growing plant species. Obviously, the white-tail population in the East did not reach its current status by creating it themselves… humans created ideal habitat for them by clear-cutting the forests. At the time of the clear cutting, deer populations declined or even were locally extirpated, but the young, second growth forests that regenerated formed patchwork with farmlands and meadows, creating ideal white-tail deer habitat. However, once that population has exploded, I believe that deer feeding habits may do much to keep that habitat ideal, i.e., disturbed.
Notice that in many places, deer and elk overpopulation are not characterized by skinny, starving ungulates, but by well-fed deer and elk on devastated rangeland with drastically reduced biodiversity.
This is only one possible aspect of the issue, but I think it is interesting. If true, then over the long haul, I think predators “check” herd size primarily by promoting a form of resource limitation (either by permitting ecological succession to different habitat, or by limiting usage of ideal habitat) rather than by direct killing of individuals (although of course, some animals are removed from the population in this way). This of course, greatly increases overall biodiversity.
In the case of cougars, open spaces may not seem like ideal places to seek prey. However, even though more covered terrain may be optimal for cougars to stalk prey, the cats no doubt go where the food actually is. Where cougars are present, they know that clearings are the best places to find deer (in the case of Zion NP, mule deer) and that deer WILL inevitably come to feed (just as lions hunt around waterholes in Africa). The deer in turn, may be forced to spend less time in clearings. Without cougars, the mulies can remain in their favored haunts with impunity, and the results are deer with bellies, an increased herd size, … and a devastated riverine ecosystem along the Virgin River that has little hope of recovery if the present condition persists.