New studies prove that predators play an essential role in maintaining the biodiversity of the ecosystems.

Scientists at the Oregon State University showed that the disappearance of cougars, Felis concolor (photo above), from parts of Zion National Park in the past 70 years has allowed a population boom of the deer, with severe ecological damage, loss of cottonwood trees, eroding streambanks, and declining biodiversity. "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 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."

"The end result is the decline or disappearance of shrubs, wetland plants, amphibians, lizards, wildflowers, and even butterflies."

Researchers now have proofs that predators not only influence through direct predation, but they also change foraging behavior of the prey species, causing "the ecology of fear."

With predators, growing and ravenous deer populations ate young cottonwood trees almost as quickly as they sprouted, leaving streambanks without shade and erosion protection. Cottonwoods may ultimately disappear in areas accessible to deer inside the Park.

By comparison, a nearby remote watershed with similar native ecology and an intact cougar population has a far lower mule deer population and nearly 50 times younger cottonwood trees as well as rich populations of flowers, lizards, butterflies, and several species of wetland plants that stabilize stream banks. "These two canyons, almost side by side, have a similar climate and their ecosystems should be quite similar. 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", said William Ripple, a professor in the OSU Department of Forest Resources.

Zion Canyon has nearly three million visitors annually, while the adjacent North Creek only few dozens of stray hikers. Cougars in Zion Canyon Park are not killed or removed, they just left due to the increased human presence stress. The sustainability of riparian habitats and biodiversity seems to need both predation of the wild ungulates as well as the fear of predation to affect their behavior.

In another study made in Australia, scientists showed that decreased number of dingoes (photo bellow) is harmful for the declining native marsupial mammals. But sheep and cattle farmers have actively poisoned the dingoes, because they are seen as harmful for their stocks. "The experience is that you really can't succeed as a sheep farmer if there are dingoes around." said Professor Chris Johnson of James Cook University in Queensland.

Since the European settling in Australia, with their array of introduced species, including foxes and feral cats, 18 species extinctions of marsupials have been documented, half of all mammals extinctions worldwide during the last two centuries, and many more severely declined.

The Dingo (Canis lupus dingo) was brought to Australia 3,500-4,000 years ago by seafarers from Indonesia and traces its roots from a semi-domestic dog in Indochina. The social dingo hunts in packs but will also scavenge.

At the moment of their introduction, they were probably responsible for the elimination of the extinct thylacine (Tasmanian "wolf") and marsupial lion from Australia, and, moreover, their entrance on the Australia's ecosystems must have provoked the same wave of decline in marsupial species like the recent introduction of foxes and cats, but after the initial moment, a balance was achieved.

Australia's last native "top predators" now perform an essential role in maintaining biodiversity. Marsupial populations have a much better chance to survive in areas that also have stable populations of dingoes, because these are the only predator to check foxes and feral cats, stopping overkill of the marsupials.

Professor Johnson would like to see areas of Australia labeled as "wild country", with dingoes accepted as a natural part of the ecosystem. "It probably won't happen across sheep land, but in cattle country dingoes will hunt kangaroos or rabbits. If there's an alternative prey available, they'll leave the cattle alone. Sheep are so easy to kill; they will be the preferred prey," he said.

"Possibly, we'd need to rethink the reasons for controlling dingoes in cattle country. The reason it is done is because dingoes do sometimes kill calves. But we really have to trade off all the costs and all the benefits of having a predator."

Dingoes also check populations of animals that compete with cattle like kangaroos, feral goats and feral pigs.

These studies may be relevant to ecosystems around the world where predators have been removed and high populations of wild or domestic grazers (such as cattle or sheep) affect biodiversity.