Cougar Predation Key To Ecosystem Health

A new study by researchers from Oregon State University found that cougars in Zion National Park have a profound impact on other aspects of the ecosystem, primarily by controlling deer populations and the ecosystem alterations related to deer browsing.

The general disappearance of cougars from a portion of Zion National Park in the past 70 years has allowed deer populations to dramatically increase, leading to severe ecological damage, loss of cottonwood trees, eroding streambanks and declining biodiversity. Researchers are calling it a “trophic cascade” of environmental degradation.

This “trophic cascade” of environmental degradation, all linked to the decline of a major predator, has been shown in a new study to affect a broad range of terrestrial and aquatic species, according to scientists from Oregon State University.

The research was just published in the journal Biological Conservation — and, like recent studies outlining similar ecological ripple effects following the disappearance of wolves in the American West — may cause land managers to reconsider the importance of predatory species in how ecosystems function.

The findings are consistent, researchers say, with predictions made more than half a century ago by the famed naturalist Aldo Leopold, often considered the father of wildlife ecology.

“When park development caused cougar to begin leaving Zion Canyon in the 1930s, it allowed much higher levels of deer browsing,” said Robert Beschta, an OSU professor emeritus of forest hydrology. “That set in motion a long cascade of changes that resulted in the loss of most cottonwoods along the streambanks and heavy bank erosion.”

“But the end result isn’t just loss of trees,” he said. “It’s the decline or disappearance of shrubs, wetland plants, amphibians, lizards, wildflowers, and even butterflies.”

Until recently, ecologists had a poor understanding of how the loss of an important predator, such as wolves or cougar, could affect such a broad range of other plant and animal species. But the evidence is now accumulating that primary predators not only have direct effects in influencing the population sizes of native grazing animals such as deer and elk — they also have indirect effects in changing their foraging behavior, in what has been called “the ecology of fear.”

That phenomenon, the scientists say, has been shown as vividly in Zion National Park as any other location they have ever studied.

In Zion Canyon, which since the early 1900s has been a popular tourist attraction, cougars are virtually absent, mostly just scared off by the huge influx of human visitors. With their natural enemy gone, growing and ravenous deer populations ate young cottonwood trees almost as quickly as they sprouted, robbing streambanks of shade and erosion protection.

As a result, floodplains began to erode away. Other types of vegetation and the animal species dependent on them suffered. And unless something is done, cottonwoods in Zion Canyon may ultimately disappear in areas accessible to deer, the researchers said.

By contrast, a nearby roadless watershed has similar native ecology but is sufficiently remote that it still has an intact cougar population and far fewer mule deer. In contrast to Zion Canyon, streambanks in this watershed have nearly 50 times more young cottonwood trees as well as thriving populations of flowers, lizards, butterflies, and several species of water-loving plants that help stabilize stream banks, provide food-web support, and protect floodplains for use by many other animal species.

“The documentation of species abundance that we have in this study is very compelling,” said William Ripple, a professor in the OSU Department of Forest Resources and lead author on the study. Researchers did a systematic survey of channel dimensions, streambank condition, vegetation and species presence along each study site.

“These two canyons, almost side by side, have a similar climate and their ecosystems should be quite similar,” Ripple said. “But instead they are very different, and we hypothesize that the long-term lack of cottonwood recruitment associated with stream-side areas in Zion Canyon indicates the effects of low cougar and high deer densities over many decades.

“It’s a great research setting and a great opportunity to assess the potential importance of a key predator,” he said. “We hope to conduct additional research in Zion National Park to further explore the findings of this initial study.”

It’s important to remember, the researchers said, that the ultimate driver behind all of these changes is humans — in the case of Zion Canyon, simply by their presence. That canyon receives nearly three million human visitors a year, the adjacent North Creek a stray handful of hikers. Cougars in Zion Canyon were not intentionally killed or removed, they just left due to the increased presence of humans.

As findings such as this — the way cougars affect deer and wolves affect elk — continue to mount, land managers may have to acknowledge the potentially enormous impact of these grazing animals on other ecosystem processes, scientists say. This could open the way to new management options once the role of herbivory by deer, elk, or other grazing animals is more fully understood.

In systems with wild ungulates, the sustainability of riparian habitats and biodiversity may require both predation on these herbivores as well as the fear of predation to further affect their behavior, the researchers concluded.

Ripple and Beschta considered other factors that may have played a role in loss of cottonwood trees in Zion Canyon, such as climate fluctuations or human interventions to stream channels, but concluded that those impacts could not have caused the enormous loss of trees and associated impacts to other biota that were found in the canyon.

The findings of this study may be relevant to other ecosystems in the U.S. and around the world where key predators have been removed, the researchers said, and high populations of native herbivores such as deer or elk — or domestic grazers such as cattle or sheep — affect native biodiversity.

This research was funded by the National Park Service.

 Story Source: The above story is based on materials provided by Oregon State UniversityNote: Materials may be edited for content and length.

Over 75 percent of large predators are declining

The world’s top carnivores are in big trouble: this is the take-away message from a new review paper published today in Science. Looking at 31 large-bodied carnivore species (i.e those over 15 kilograms or 33 pounds), the researchers found that 77 percent are in decline and more than half have seen their historical ranges decline by over 50 percent. In fact, the major study comes just days after new research found that the genetically-unique West African lion is down to just 250 breeding adults.

“Globally, we are losing our large carnivores,” says lead author of the study, William Ripple, with Oregon State University. “Many of them are endangered. Their ranges are collapsing. Many of these animals are at risk of extinction, either locally or globally. And, ironically, they are vanishing just as we are learning about their important ecological effects.”

The story of the world’s large carnivores is a largely bleak one. In the not so distant past, most people—even scientists—largely viewed large carnivores as competitors, pests, and deadly threats. Such views led to conflict and even extermination campaigns that killed-off many of the world’s top predators in Europe, North America, the Middle East, and North Africa, and decimated populations elsewhere. In fact, the study finds that 66 percent of the 31 biggest carnivores are currently listed as threatened on the .

The  has lost 35 percent of its historical range and is decreasing. Photo by: Kirstin Abley.

“These carnivores often require large prey and expansive habitats,” write the scientists. “It is these food requirements and wide-ranging behavior that often bring them into conflict with humans and livestock. This, in addition to human intolerance, renders them vulnerable to extinction.”

In many parts of the world, top predators are still shot, trapped, poisoned, or even speared. Even where they are not directly targeted, big predators are rapidly losing both their habitat and their prey base, leading to a trend of vanishing top predators even in protected areas.

According to the study, the major trend underpinning this global decline in big predators is the rapidly-rising population of another predator: humans.

“An increasing human population and subsequent rate of urbanization inevitably means many habitats will be further reduced or modified. This will place top predators at increased risk of extinction,” co-author Euan Ritchie with Deakin University in Australia told, adding that “the issue of an increasing human population poses challenges well beyond just maintaining top predators in the environment. How we are going to produce enough food while still maintaining the biodiversity we are so dependent upon is arguably society’s greatest challenge.”

However, even as most big-bodied predators continue to decline, popular views of these megafauna are slowly shifting. Large-bodied predators now have many conservation champions, and elucidate passionate responses from advocates. These animals are also often seen as key symbols for global conservation efforts, and in some parts of the world (notably the U.S. and Europe) a few big predators are staging mini-comebacks. But perhaps, more importantly, scientists are just beginning to understand the outsized role of big carnivores in the world’s ecosystems.

Sea otters play a major role in the health of kelp forests. Photo by: Norman S. Smith.

“There is now overwhelming evidence from around the world that we are better off with top predators in the environment because of the many important roles they perform, such as reducing overgrazing of vegetation by herbivores which increases the carbon sequestration capabilities of habitats and in turn assists with ameliorating the impacts of climate change,” says Ritchie.

In fact, scientists have long theorized that big predators exert a powerful ecological influence on the foodchain by keeping herbivore populations low, but now they are discovering additional avenues in which big carnivores impact ecosystems. For one thing, top predators also keep mesopredators (medium-sized predators) in check via harassment, intimidation, and sometimes downright killing. Losing big predators can mean a sudden explosion of mesopredator abundance, impacting species all down the line. For example, Australia has built a massive fence that keeps the dingoes (Canis lupus ) out of sheep grazing areas. However, in these same areas, —an invasive predator—runs amuck, leading to increased pressure on native mammals.

“Overall, the suppression of dingoes has probably contributed to the endangerment and extinction of small marsupials and rodents over much of the continent,” the scientists write.

The unmistakable importance of predators is not regulated to the land alone. Research has shown that sea otters (Enhydra lutris) exert a huge influence on their environment by keeping urchin populations in control. When sea otters are killed off, sea urchin populations explode, decimating kelp forests. The researchers write that sea otters “[enhance] the abundance and distribution of kelp and other fleshy macroalgae in coastal inshore ecosystems.”

 in : the top predators were reintroduced into the park after a 70 year absence. Photo by: Doug McLaughlin.

Probably the most famous example of the importance of top predators comes from Yellowstone National Park. The reintroduction of wolves into the park in the 1990s has had massive impacts on the ecosystem. With the return of the wolves, elk behavior changed significantly: instead of browsing out in the open, they took to the forests for protection. This allowed trees to grow unimpeded in many parts of the park where they had been overgrazed for decades, including along river and stream beds. The impacts spread to songbirds, beavers, fish, overall biodiversity and even carbon sequestration. In a roundabout way, wolves became the true aborists of Yellowstone.

The American  is the world’s only bear species whose population is on the rise. Photo by: Public Domain.

The  is the world’s only bear species whose population is on the rise. Photo by: Public Domain. “I am impressed with how resilient the Yellowstone ecosystem is. It isn’t happening quickly everywhere, but in some places, ecosystem restoration has started there,” says Ripple. “Nature is highly interconnected. The work at Yellowstone and other places shows how one species affects another and another through different pathways. It’s humbling as a scientist to see the interconnectedness of nature.”

Given this changing understanding of predator importance, Ritchie says many of the world’s governments are woefully mismanaging their predator populations.

Gray wolf in Yellowstone National Park: the top predators were reintroduced into the park after a 70 year absence. Photo by: Doug McLaughlin.

“In the case of wolves in North America and dingoes in Australia, their lethal control often fractures social structures leading to more not less wolves and dingoes and often increased not decreased attacks on livestock,” says Ritchie, who argues that policies of culling predators “potentially [exacerbate]” human conflict with predators” and undercut ecosystem services.

“Governments should instead promote policies and actions such as using guardian animals for protecting livestock, as this will lead to improved and sustained environmental and economic outcomes,” he adds.

But how many predators are needed to fulfill their ecological role? In many cases, scientists aren’t wholly certain, but Ritchie says the answer is actually more complex than a simple number.

“It’s not just how many predators there are but the age and sex of individuals is important. When predator populations are greatly reduced and interfered with through lethal control, relationships between individuals breakdown and predators can behave in unexpected and sometimes very negative ways,” he notes. In many predatory species, infants and adolescents learn from older individuals. When mature individuals are killed-off, young predators are left without their mentors, often leading to more erratic behavior and posing a higher risk both to livestock and people.

Despite growing knowledge about the importance of top predators, the ecological role of most of the world’s large-bodied predators remains unknown. Perhaps more alarming still, scientists lack good data on the population sizes of many of the world’s top predators, leaving conservationists guessing. But where information is available: it is disheartening. Lion populations have fallen from an estimated 100,000 in 1960 to 15,000-35,000 today. There are currently more captive tigers in the U.S. alone than there are tigers in the wild worldwide (about 3,200). The Ethiopian wolf () has lost 98 percent of its historical range and sports a total population of less than 500.

Not all the news is bleak: wolves are returning to long-lost habitats in the U.S. and Western Europe, conservationists have launched a massive campaign to double tiger numbers in the wild by 2022, and the world’s rarest big predator—the red wolf (Canis rufus)—is bouncing back after once being thought totally extinct. However, the bad news—and the relentless pressures—very much outweighs the good for the world’s big predators.

“Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth’s largest carnivores and all that depends upon them, including humans,” the scientists conclude.

The dingo fence is one of the longest structure on the planet, stretching for 5,614 kilometers (3,488 miles).

Wolves killed in Russia. In much of the world, governments still practice massive culling measures to manage carnivores.

The Javan tiger, a distinct subspecies, went extinct in the 1970s. Photo by: Public Domain.


  • W.J. Ripple, R.L. Beschta, M.P. Nelson, et al. Status and Ecological Effects of the World’s Largest Carnivores. Science (2014) Vol 334.

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The world’s top predators are in decline, and it’s hurting us too

Humans have an innate fear of large predators, and with good reason. Nobody wants to be a shark or a lion’s next meal.

But new research in the journal Science shows that our inability to live with these animals is putting their survival in great danger, and doing untold damage to the environment.

Through modifying the habitats of large predators or killing predators more directly, we are greatly compromising the ecosystems that they help to keep in balance — free of charge. In turn this environmental degradation creates many problems that have severe consequences for humans.


We ain’t lion, this predator stuff is a big deal. Flickr/Derek Keats
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Top dogs (and cats) under threat

For the first time, a team of researchers from the United States, Australia, Italy, and Sweden, and led by Professor Bill Ripple at Oregon State University, have analysed the effects of threats such as habitat loss, human persecution and reduced prey on the world’s 31 largest mammalian carnivores.

The species studied include lions, tigers, African wild dogs, leopards, cheetahs, wolves, lynx, otters, bears, hyenas and dingoes. Together they span all continents except Antarctica.

Alarmingly, more than three quarters of the 31 large carnivores are in decline, and 17 species occupy less than half of their historical distributions. The Red Wolf in the southeastern United States is now found in less than 1% of its historical range, and theEthiopian Wolf in just 2%.

Hotspots of carnivore decline are southeast Asia, southern and East Africa, and the Amazon, where several large carnivores are declining. And in the developed world there are now few places where large carnivores remain.


In Australia, dingoes help keep introduced predators at bay. Flickr/Ars Electronica
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Aside from the intrinsic tragedy of losing any species, what should perhaps concern us even more is that we are only just beginning to understand and appreciate just how important large predators are to maintaining healthy ecosystems, and our dependence on the ecosystem services they deliver.

Ripple effect

Seven carnivore species in particular have been shown to have profound effects on the environment and cause what is known as “trophic cascades”. A trophic cascade is a ripple effect, where one species’ influence spreads through multiple levels of a food web.

Species for which this effect is most well-known are African lions, leopards, Eurasian lynx, cougars, gray wolves, sea otters and dingoes.


It’s hard being a VIP (very important predator). Flickr/Mike Baird
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In Australia dingoes greatly reduce kangaroo and red fox numbers, which in turn reduces grazing of vegetation and predation of native animals, helping to conserve and protect biodiversity.

In coastal North America, sea otters keep sea urchin numbers in check, which helps maintain kelp forests and benefits other marine species dependent on this habitat. But in this case otters might also offer a defence against climate change, as healthy kelp forests can grow rapidly and store large amounts of carbon.

And in Africa, a decrease in lions and leopards has coincided with a dramatic increase inOlive Baboons, which threaten farm crops and livestock, and spread intestinal worms. Baboons even impact education, as children have to stay home to defend their farms from raids.


Without lions and leopards, there’s no telling what baboons will do. Flickr/JustinJensen
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Clearly predators have far-reaching ecological, economic and social benefits that are grossly underappreciated. There is no doubt predators pose challenges too, such as wolves attacking livestock. But education and new management practices offer ways forward. For instance, we could use guardian animals to protect livestock from predators.

Together we call on governments to end policies and management practices that are responsible for the ongoing persecution and loss of predators from our planet. Western Australia’s new shark plan is an example of management that fails to account for the science of big predators. Instead we need an international initiative that aims to conserve large predators and promote their coexistence with people.


John Terborgh: The Trophic Cascade Regulates Biodiversity

“The Trophic Cascade Regulates Biodiversity”

John Terborgh, Research Professor in the Nicholas School of the Environment and Earth Sciences at Duke University; Director of the Duke University Center for Tropical Conservation

In this presentation, Dr. Terborgh draws on his decades of ecological research in the Neotropics to explain how biological interactions intricately regulate biodiversity. Hypotheses on the maintenance of tropical forest diversity abound, but it is becoming increasingly recognized that interspecific interactions are vital to sustaining the rich diversity the tropics are famous for. Dr. Terborgh offers ecological insights on the regulation of biodiversity and describe how interactions between primary producers, herbivores, and their predators contribute to the richness of tropical forests.

PGE’s interdisciplinary Spring conference, “Conserving More Than Carbon: Valuing Biodiversity in a Changing World”, addressed the current state of knowledge of tropical forest diversity and outlooks for its protection.

Learn more about the conference and the participants at:

Why the Beaver Should Thank the Wolf

THIS month, a group of environmental nonprofits said they would challenge the federal government’s removal of Endangered Species Act protections for wolves in Wyoming. Since there are only about 328 wolves in a state with a historic blood thirst for the hides of these top predators, the nonprofits are probably right that lacking protection, Wyoming wolves are toast.

Image: Jungyeon Roh

Many Americans, even as they view the extermination of a species as morally anathema, struggle to grasp the tangible effects of the loss of wolves. It turns out that, far from being freeloaders on the top of the food chain, wolves have a powerful effect on the well-being of the ecosystems around them — from the survival of trees and riverbank vegetation to, perhaps surprisingly, the health of the populations of their prey.

An example of this can be found in Wyoming’s Yellowstone National Park, where wolves were virtually wiped out in the 1920s and reintroduced in the ’90s. Since the wolves have come back, scientists have noted an unexpected improvement in many of the park’s degraded stream areas.

Stands of aspen and other native vegetation, once decimated by overgrazing, are now growing up along the banks. This may have something to do with changing fire patterns, but it is also probably because elk and other browsing animals behave differently when wolves are around. Instead of eating greenery down to the soil, they take a bite or two, look up to check for threats, and keep moving. The greenery can grow tall enough to reproduce.

Beavers, despite being on the wolf’s menu, also benefit when their predators are around. The healthy vegetation encouraged by the presence of wolves provides food and shelter to beavers. Beavers in turn go on to create dams that help keep rivers clean and lessen the effects of drought. Beaver activity also spreads a welcome mat for thronging biodiversity. Bugs, amphibians, fish, birds and small mammals find the water around dams to be an ideal habitat.

So the beavers keep the rivers from drying up while, at the same time, healthy vegetation keeps the rivers from flooding, and all this biological interaction helps maintain rich soil that better sequesters carbon — that stuff we want to get out of the atmosphere and back into the ground. In other words, by helping to maintain a healthy ecosystem, wolves are connected to climate change: without them, these landscapes would be more vulnerable to the effects of those big weather events we will increasingly experience as the planet warms.

Scientists call this sequence of impacts down the food chain a “trophic cascade.” The wolf is connected to the elk is connected to the aspen is connected to the beaver. Keeping these connections going ensures healthy, functioning ecosystems, which in turn support human life.

Another example is the effect of sea otters on kelp, which provides food and shelter for a host of species. Like the aspen for the elk, kelp is a favorite food of sea urchins. By hunting sea urchins, otters protect the vitality of the kelp and actually boost overall biodiversity. Without them, the ecosystem tends to collapse; the coastal reefs become barren, and soon not much lives there.

Unfortunately, sea otters are in the cross hairs of a conflict equivalent to the “wolf wars.” Some communities in southeast Alaska want to allow the hunting of sea otters in order to decrease their numbers and protect fisheries. But the rationale that eliminating the predator increases the prey is shortsighted and ignores larger food-web dynamics. A degraded ecosystem will be far less productive over all.

Having fewer fish wouldn’t just hurt fishermen: it would also endanger the other end of the trophic scale — the phytoplankton that turn sunshine into plant material, and as every student of photosynthesis knows, create oxygen and sequester carbon. In lakes, predator fish keep the smaller fish from eating all the phytoplankton, thus sustaining the lake’s rate of carbon uptake.

Around the planet, large predators are becoming extinct at faster rates than other species. And losing top predators has an outsize effect on the rate of loss of many other species below them on the food chain as well as on the plant life that is so important to the balance of our ecosystems.

So what can be done? For one thing, we have begun to realize that parks like Yellowstone are not the most effective means of conservation. Putting a boundary around an expanse of wilderness is an intuitive idea not borne out by the science. Many top predators must travel enormous distances to find mates and keep populations from becoming inbred. No national park is big enough for wolves, for example. Instead, conservation must be done on a continental scale. We can still erect our human boundaries — around cities and towns, mines and oil fields — but in order to sustain a healthy ecosystem, we need to build in connections so that top predators can move from one wild place to another.

Many biologists have warned that we are approaching another mass extinction. The wolf is still endangered and should be protected in its own right. But we should also recognize that bringing all the planet’s threatened and endangered species back to healthy numbers — as well as mitigating the effects of climate change — means keeping top predators around.

Mary Ellen Hannibal is the author of “The Spine of the Continent.”


Predators and their prey – why we need them both

by Joe Scott, international conservation director

Originally published in the spring/summer 2011 edition of Conservation Northwest Quarterly

Like CSI detectives investigating a crime scene, lynx and hare researchers in north central Washington recently responded to a “mortality” signal from a snowshoe hare that they had fitted with a satellite tracking collar to monitor hare movements. When they arrived at the scene the biologists were able to reconstruct the events around the hare’s demise.

Predators & prey: Why don’t predators eat all their prey?

A great horned owl had killed the hare, but predator became prey as a lynx killed the owl and pirated the hare for itself.

Everything eats snowshoe hares. In boreal forests, hares are the cheeseburgers for the fries, the fish for the chips, the meatballs for the spaghetti, and the corned beef for the cabbage.

Lynx are the most famous hare junkies, but the fleet-footed rabbits are also favored by wolves, coyotes, foxes, martens, eagles, goshawks, owls, and other raptors. In the ultimate insult, even red and ground squirrels eat them. People eat them.

Speed, stealth, aerial ambush and traps are all used on hares. Cute has no currency in the wilds, except as lunch. Scott Fisher, biologist with the Washington Department of Natural Resources, describes it this way: “When you’re a hare, everybody else on the block is a bully.”

But despite being every animal’s comfort food, snowshoe hares not only persist but do so in often ridiculous numbers.  How does an animal in such demand avoid being eaten out of existence?

It’s tempting to think that hares’ prodigious breeding ability is the evolutionary response to hyper predation.

But we have to dig a little deeper. All animals will have as many babies as they can successfully rear, whether their eggs are small and many or large and few, because that’s the best way of ensuring your genes survive in competition with those of your neighbors. And whether a species has many, many small eggs like a salmon, or a couple large eggs like a grizzly bear, it’s all about getting more of your genes out there, which is in turn rooted in the concept of ecological niches.

Predators & prey: What is a niche? Jobs in the woods


Paul Colinvaux describes a species’ niche as its place in the “grand scheme of things,” its “profession,” that is, “everything it does to get its food and raise its babies.” A plant or animal’s habitat is its address.

Spaces in each ecological niche, like welding jobs in a shipyard, are limited. Consequently the number of species that can fill a particular niche is more or less set by limitations on habitat imposed by climate, food, den sites, cover, etc—all the things that a species needs to survive and reproduce.

The niches, or jobs, of each species are crafted over millennia by natural selection. In other words, as Colinvaux concludes, “the common stay common and the rare stay rare,” unless something drastic happens to change the environment, like, for instance, clear cutting an old-growth forest or deregulating the financial industry. In each case you have a proliferation of weedy species, a reduction in diversity, and fewer real jobs.

Snowshoe hares have evolved to exploit a niche that has few competitors, since the boreal forests home to hares and lynx are very tough neighborhoods, especially in winter. In other words there are lots of hare “jobs” out there as long as the boreal remains the boreal and something doesn’t happen to radically alter it—like climate change.

So hares have lots of babies, very often, to supply the demand for hare jobs, not because so many animals like to eat them. High hare predation rates are a consequence of hare fecundity not a cause. Hare deaths are the grim cost of a reproductive strategy that floods the market with baby rabbits. And, lots of hares provide hare eating niches, or jobs, for many different predators.

So ultimately the numbers of any wildlife species are not determined by breeding strategies. They are set by opportunities for a particular plant or animal to live according to its needs. The number of welding jobs in the shipyard, not graduates of welding schools, determines the jobs for welders.

Predators & prey: Natural selection: Nature’s golden rule

Cooperation and conflict drive plant and animal adaptation. Species and their habitats thrive as interactive, dynamic systems that are constantly reshaping each other.

Natural selection is the ultimate arbiter—the universal law by which Mother Nature governs the biosphere. Quite simply, organisms are driven to survive, so prey animals respond over time with physical and behavioral adaptations to all the natural forces and conditions that conspire to kill them. Predators respond in kind with adaptations that allow them to exploit particular prey species. Otherwise neither would survive.

Predators have helped make snowshoe hares, well, snowshoe hares. Natural selection has equipped them with outsized hind legs and feet to run at lightening speed over snow. Their huge ears magnify the slightest sounds. Most ingeniously from a genetic standpoint, hares have developed a natural camouflage and change color with the seasons—white for winter, brown for summer. With so many things trying to eat them, they need lots of defensive weapons.

The hares that live longest and have the most babies pass more of those successful genes to the next generation, refining the traits over time, like camouflaged fur, that allow hares to escape lynx and owls long enough to reproduce, thus ensuring the survival of the species and its competitive “fitness” to adapt to dynamic landscapes and dozens of hungry predators.

Lynx are the ultimate hare specialists and as such their fortunes rise and fall with those of their big-footed prey. And they’ve kept pace in the evolutionary race for survival: their huge furry feet and long hind legs allow them to run and cut on top of snow like an NFL running back on juice. Many animals hunt hares but none with the efficiency of lynx. Yet they still can’t kill all the hares.

Predators & prey: Wild fluctuations

bighorn-does-david-moskowitz.jpgIn the north of their range, hare numbers have historically “crashed” spectacularly before rising again dramatically. In Alaska and western Canada, hare numbers rise and crash in roughly 10-year cycles, sometimes going from 10,000 to fewer than three animals per square mile in a single year. Female hares can produce two to five litters per year with three to four young per litter.

The phenomenon has been a source of scientific scrutiny for decades and was first described by fur trappers in the mid-nineteenth century. On large scales, scientists think that cyclical sun spot activity affects weather patterns and fire frequency in boreal forests, which in turn affect hare survival and food availability.

On smaller scales, over-browsing by the hyper-reproductive hares at their population zenith leads to food shortages that cause starvation and reduced reproduction, which in turn start the population declines. Just as the health of individual hares diminishes and they become more vulnerable to disease, predation from a larger number of hungry hare eaters kicks in and bingo, hares are scarcer than hens’ teeth—for a little while.

In essence, such wild fluctuations “reset” complex multiple predator prey systems until the next crash, rather like the way our economic and regulatory systems work—or not. Since they’re so tightly linked to snowshoe hares for food, lynx populations in the north rise and fall with them.

Northern lemmings undergo similar population booms and busts. Snowy owls are so tuned in to lemmings that they actually lay fewer eggs when lemming populations are down.

But such boom and bust predator prey economies are the exceptions, not the norms.

Predators & prey: From Arctic to Africa

Bees swarm, birds flock, fish school, and ungulates such as elk form herds because they’re less likely to become a predator’s next lunch special if they do so. Why some predators form groups, on the other hand, like lions in prides or wolves in packs, could have less to do with food sharing and more with defense of territories and rearing of young.

Research on the most well-known predator/prey dance partners on earth has shown that Africa’s Serengeti lions and wildebeest coexist in relative stability without the dramatic fluctuations in numbers that typify some arctic predators and prey like lynx and hares and lemmings and snowy owls.

A research team lead by John Fryxell of University of Guelph in Canada and Craig Packer from the University of Minnesota wanted to know why. Their modeling of four decades of data showed that wildebeest drastically reduced lion predation when they kept to groups and large herds.

Interestingly, the greater the tendency to form groups, the higher the stability of numbers of both species over time. According to Fryxell and colleagues: “When both the lions and wildebeest formed groups, predation was reduced even more. Compared with no-group ecosystems (all animals strewn across the Serengeti), grouping caused a 90-percent reduction in kill rates for lions.”

The complex social “cliques” seemed to work as ecosystem stabilizers, not dissimilar to human communities, with “both lion and wildebeest populations remaining relatively level over time.”

Social cliques among wild animals in the Serengeti are actually the glue that holds the ecosystem together and keeps population numbers stable. Wildebeest thrive in great numbers alongside zebra, Thompson’s gazelles, and several other ungulate species, all prey for lions, leopards, hyenas, crocodiles, hunting dogs, and cheetahs.

Predators & prey: Wolves and white-tails

There are 3,000 wolves in Minnesota. They eat on average about 50,000 of the estimated 450,000 white-tailed deer a year. This represents about 11.5 % of the deer population, with minimal supplements of snowshoe hares, beavers, and moose.

In a recent comprehensive 15-year study of white-tailed deer and wolves, the Minnesota Department of Natural Resources (MDNR) monitored the movements, survival, and mortality causes of 450 radio-collared does in four study areas. Simultaneously, department biologists monitored 55 radio-collared wolves from eight packs whose territories overlapped the deer study areas.

The research showed that doe mortality from wolves ranged from 4% to 22% per year but most typically was between 5% to 10% per year with the highest rate observed in the very severe winter of 1995-96.

Despite the fact that deer outnumber wolves in Minnesota by 150 to 1, wolves are not particularly effective hunters of white-tails.

According to the MDNR, “Wolves end up surviving primarily on the most vulnerable individuals in the deer population, such as very young, old, sick, injured, or nutritionally compromised deer, because those are the ones they can catch. The result being, that under certain conditions…many of the deer that wolves kill likely would have died from other causes, such as starvation or disease.”

Biologists refer to such predation impacts as “compensatory” as opposed to the “additive” effects of human hunters, who kill most prey in the prime of their reproductive lives.

Predators & prey: Where have all the mule deer gone?

doe-mule-deer-looking-out-david-moskowitz.jpgResearchers from Washington State University wanted to understand the reasons for long-term mule deer declines in the intermountain West. Hunters had long been blaming cougars. They were right…sort of. Cougars do kill mule deer. So do wolves, coyotes, bobcats, black bear, and grizzly bears.

But as with all natural systems, nothing’s that simple.

It turns out that the open, mixed forest habitat preferred by mule deer has been so dramatically altered in the West through irrigated agriculture that it’s provided wonderful white-tailed deer habitat. White-tails, historically rare in Washington, now outnumber mule deer in eastern Washington.

And as white-tailed deer numbers grow, mule deer decline. It appears as though landscape level habitat changes have created the white-tailed equivalent of tenements for cockroaches. It also appears that cougars have responded in kind.

But while there may be a slight uptick in cougar numbers as a result of increased ungulate numbers, cougar numbers have not exploded as some people seem to think.

“It’s particularly striking how little difference there is in resident cougar densities across cougar range in western North America,” says Gary Koehler, carnivore biologist, Washington Department of Fish and Wildlife. According to Dr. Koehler and his colleagues, “North American cougars exist in densities of about 1 to 2 adult animals per 100 sq. km everywhere they live—almost without fail. Female cougars are limited by prey availability, but males are limited by the availability of females in their territories, which they defend vigorously.”

However, the WSU researchers have found that cougar predation is having a greater impact on mule deer than on white-tails and occurs in the summer when white-tails move into higher elevation mule deer habitat. Mule deer are the “secondary” prey, but as they’re already in decline, predation is having a greater effect on them.

A similar dynamic has happened with mountain caribou in British Columbia’s inland rainforest. As the caribou’s historically extensive old-growth forest habitat has been increasingly fragmented, it’s opened more niches for deer, elk, and moose. Cougars and wolves follow and opportunistically prey on caribou which cannot withstand the “new normal.” For centuries the mountain caribou old forest and high elevation niche was at the heart of their predator avoidance strategy. Predators simply weren’t able to get to them enough to make a difference in caribou numbers.

Like steelworker jobs in Pittsburgh, jobs for mountain caribou have diminished. Now the wolves are literally at the door and it’s forced some tough choices for managers and conservationists alike until the habitat and historic prey species numbers are restored.

The Mule Deer Working Group of the Western Association of Fish and Wildlife Agencies has been studying mule deer dynamics, particularly mortalities and predation.

According to their findings, many factors confound the question about mule deer declines. Most deer mortality occurs in young animals soon after birth or in winter of their first year. Some biologists believe that the question of whether mortality is compensatory or additive is density dependent—it has to do with how many of the mule deer jobs are filled—also referred to as “carrying capacity” or the ability of the habitat to support the herd.

Carrying capacity can be measured by the overall condition of the animals and their range. When the herd numbers are consistent with what the habitat can support—at carrying capacity—deaths that happen are compensatory. They will occur one way or another naturally keeping animals at levels where the land to support them. As numbers of deer fall below range capacity, additional deer deaths become additive—and unsustainable, contributing to herd declines.

Climatic conditions such as long-term drought or severe winters can reduce the quality of the range and thus the overall physical condition of mule deer making them more vulnerable to predation. Significant habitat changes that result in different movement patterns could make deer even more susceptible to predation.

According to the Working Group, “…most of the environments where mule deer exist today have been altered by fire suppression, development, habitat fragmentation” etc. In these habitats (most of the West), biologists believe predation does not cause declines in deer populations. The effect predators have on prey populations in these environments is more complex and related to how humans affect predators, prey and habitat, and the types and densities of predators that exist.

“In years when mule deer populations are lean, some predators such as mountain lions and wolves may consume several wildlife species including elk and small mammals, causing the predators to maintain artificially high numbers. While this has the potential to slow the growth of mule deer populations, scientific studies show that reducing predators does not increase the number of fawns that survive to adulthood. And it’s the number of fawns that survive to adulthood that determines the growth rate of a mule deer population.”

Predators & prey: Why big fierce animals are rare

lynx-hunting-photo-c-patrick-reeves.jpgEverybody knows that, in nature, small things are common and large things are rare. To understand why, we need to dust off our high school physics textbooks and reacquaint ourselves with the second Law of Thermodynamics, which dictates that the harvesting of solar energy cannot be 100% efficient. This is the real reason that big fierce animals are rare. And rarity is one reason that predators can’t eat all their prey or compromise their numbers to the point that those prey animals are themselves threatened as species.

Ecosystems have structure, like the rows of stone in a pyramid. This structure is organized into what ecologists call “trophic levels,” which are quite simply the different plant and animal communities that inhabit a given area. In a typical simple system there are three trophic levels: plant communities, herbivores, and carnivores. Plants form the large pyramid base, herbivores in the middle level, carnivores at the small, pointy top.

Plants are less than 10% efficient converting light energy to produce plant tissue. Ninety percent is lost as heat to the atmosphere. In the transfer of energy to the second trophic level, the herbivores follows suit, so essentially energy is degraded by 90% at each level from plants through herbivores to carnivores. Of the 1000 calories of solar energy captured by a plant, 100 calories are available to a deer, and 1 calorie is available to a wolf, to grow, reproduce, and have enough strength and energy to hunt again. For this simple reason alone, predators generally can never number more than 10% of their prey.

The upshot is that predators have to work really hard to make a living. It’s definitely blue collar: complete with long hours, physical exertion, shorter life span, high risk of injury or death, and being frequently ostracized by neighbors. For example, wolves are considered efficient hunters for only about two years of their lives and rarely live beyond seven years in the wild.

Predators are limited by available calories, particularly in winter, territorial behavior, the rigors and risks of hunting, rapid decline in their athletic abilities. It’s no life of Reilly. The Second Law of Thermodynamics and natural selection have seen to it.

Predators & prey: Balance in all things

The bottom line is that ecosystems are complex. And, like it or not, predators are a necessary and beneficial part of natural systems. If we remove them from the picture, there are consequences.

Predators provide ecological stability by regulating the impacts of grazing and browsing animals, thus ensuring the overall productivity of the habitat. They cull weak, sick, and old prey, thus ensuring the maximum fitness of elk, deer, antelope, and hares. They foster biological diversity by “enforcing” ecological boundaries or preventing what ecologists refer to as “competitive exclusion,” the tendency of one prey animal to outcompete another. So-called “apex predators,” the wolves, lions, and tigers are the Godfathers, as they also control the numbers of “meso predators,” the coyotes, raccoons, possums, foxes—even domestic cats—which when left unchecked can do enormous damage to birds and native rodents.