Keystone Species: How Predators Create Abundance and Stability

Wolves, bears, otters, starfish — these ecosystem engineers affect nature in overt yet surprisingly subtle ways.

| June/July 2011


Long reviled as beasts of waste and desolation, wolves — along with other keystone predators — actually bring ecological stability to the habitats in which they live.


The day came clouded and wind-tossed, with 5 inches of fresh snow in the valley and a lot more piling up overhead on the peaks. It was early December in Montana in Glacier National Park. Although winter wouldn’t officially start for another two weeks, blizzards and bitterly cold temperatures had long since sent the bears into their dens.

But not every bear.

Very large, very fresh paw prints on the trail in front of me said at least one grizzly wasn’t ready to call it quits for the year.

Sleeping in underground dens keeps bears safe and insulated through the snow-smothered months while they live off reserves of fat. The biggest and most powerful ones — adult male grizzlies — sometimes leave their hidden chambers to roam about during midwinter thaws. Before, few naturalists realized these heavy-bodied bears could stay out through much colder conditions as long as they were able to take in more energy from food than they burned trying to find it. Then wolves returned to the American West.

The Food Web Surrounding Wolves

After an absence of half a century, wolves came back to Glacier during the 1980s, trotting across the border from neighboring Canadian wildlands. Suddenly, this Rocky Mountain landscape held more carcasses of deer, elk and moose, and those of us who frequented the slopes began to discover a few scavenging grizzlies later and later into the frozen season. One valley, with prime wintering grounds for hoofed herds, hosts a big male silvertip grizzly that I’m not sure ever holes up to snooze anymore.

Wolverines, with their unsurpassed nose for leftovers, can find more meals now as well. So can wintering bald eagles and golden eagles, along with northern ravens, which often follow wolf packs on the prowl. Wildlife biologists tracking the wolves discovered them taking over fresh kills made by mountain lions. In many cases, the packs seemed to be honing in on the sight of circling ravens or the birds’ excited calls in order to find the stealthy cats and drive them off their prize. Before wolves were reintroduced to Yellowstone National Park in the mid-1990s, cougars had expanded their range to include broad valley bottoms. After the wolves’ return, the cougars retreated to the steeper, more broken upland terrain they had normally hunted.

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2/13/2012 6:25:15 PM

The Keystone Species article was an interesting article on how a predator/prey relationship operates in a pristine environment. What the article failed to recognize is the presence of man which prevents the system from operating as described. As a prey species declines over time the predator population should also decline over time. Due to the presence of man and livestock (including pets), domestic species of all shapes and sizes provide predators with an un-natural source of food to call upon when times get tough. Aged predator members can also extend their lives beyond what would normally occur if they had to survive entirely off wild prey. None of this even takes into account rogue predators that discover it is easier to hunt and kill domestic species than wild prey. The uninvolved minimize the loss inflicted by predators as it isn't their cattle, sheep or birds being killed. It is an entirely different matter when you are being directly impacted. As long as man is present I am afraid the Keystone Species theory is not going to be as self regulating as the author would like to suggest.

t brandt
6/14/2011 8:29:39 PM

Excellent article showing the inter-locked web of life. Natural popualtions are in dynamic balance: alter one and the others must change to compensate. It's nice to see some science here instead of the usual drivel from The Bambi Institute of Environmentalism. To the other commentors: National Parks are supoposedly set up to preserve real nature. If you don't want to come across a 120 lb wolf, stay in Central Park where it's safe, but not natural. OTOH- wolves that wander off the preserves and molest domestic livestock must deal with the economic realities facing ranchers/farmers. As pointed out, PV-powered fencing may serve well on small acreages, but not large ranches. Ya gotta do what ya gotta do.

J Russell Bailey
6/7/2011 4:50:22 PM

Murray, You my dear fellow have zero clue concerning fences, boundaries, and most assuredly you have no clue as to size differences between ranches/farms East of the Missouri river and West of the Missouri river. I live in Wyoming and a 'small ranch' can be a mere deeded section (640 acres) to one encompassing 30k to 50k acres of deeded land. Most ranches with deeded acres also lease BLM acreage (usually for generations for these family ranches) in the thousands to tens of thousands of acres. You simply CANNOT lay 'electrified' fence on that much ground: cost prohibitive. Fire is also a serious concern for those handful that might have pockets deep enough to actually afford the hardware and monthly electric bill. You big city/small acreage folks need to STOP watching PBS and Animal Planet!

6/6/2011 11:35:49 PM

T Law and Stan W - the Isle Royale study - now in its 53rd year - tends to support the gist of this article. Google that study if you wish. The logic is there but farmers have to maintain their herds in conjunction with the environment - an environment that has predators. It adds very little to the expense of farming to install boundary electric fences which deter most wild animals as well as maintaining my (your) own stock within those bounds. Wolves leave electric fences severely alone. Worse than wolves, by far, are packs of feral dogs (let loose by their owners when they became inconvenient to house or feed), which do hunt for the "fun" of tearing a sheep flock to pieces. I speak from experience - and that experience is 000 shot as the proper answer. Black bears don't like electric fences either - nor do deer or elk. A simple solution at a reasonable cost. Foxes keep the ground-hogs in check and they have worked out how to get through the electric fence - which none of the other predators have managed - as yet.

6/6/2011 8:30:11 PM

I disagree with specific "keystone" species in light of the fact that in an ecosystem energy flows in continuous cycle. It doesn't move bottom up or top down. Remove any predator or pray species within this system and you change the habits of each and therefore energy available that cycles in that system. This has been demonstrated with rabbit populations where they eat and breed to the carrying capacity of the environment and the population crashes and the system once again comes into equilibrium.

T Law
6/6/2011 1:27:47 PM

TOTAL wolf scat. The Canadian Wolf is taking over, they kill for the fun of it! Many grow to 120 pounds. Do you want to meet one of those while trekking in Yellowstone??

Stan Wawrzynak
6/6/2011 7:53:54 AM

Introducing predators is great lets put bears and wolfs in Central Park along with rattle snakes we can't just pretend to have a perfect balance in Yellowstone to make us feel good. Balance needs across the country predators know no boundary. Lets not just pick the cute ones snakes are an important for mice and rat control.

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