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.
Source: http://www.sciencedaily.com/releases/2006/10/061024214739.htm

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 mongabay.com., 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.

Citations:

  • 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.

This article was written by  for Mongabay.com

Source: http://focusingonwildlife.com/news/over-75-percent-of-large-predators-declining/

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.

Source: https://theconversation.com/the-worlds-top-predators-are-in-decline-and-its-hurting-us-too-21830

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: http://pge.uchicago.edu/biodiversity