Predators. . . Around the world, predators are practicing survival of the fittest. This surviving has been in action for more than a million years for most species. However, extinction rates post human-introduction have multiplied by the hundreds, possibly thousands. This question, then, is posed: Why are so many species now disappearing at an accelerated pace?

The sleek, sheen coat of the cougar might for a moment distract you from the glistening canines capable of ripping flesh from bone. Sunning at the zoo, these ‘big cats’ hardly appear to retain their natural predatory ways. Here, safely locked away behind thick glass walls, they stimulate our curiosity, our interest, even perhaps our desire. One can be captivated by the power of the majestic, fluid movements of these magnificent creatures. Still, this awe and amazement has done little to aid the cats in surviving the onset of humans. The cougar population, much like that of the gray wolves, has steadily declined with the increase of human populations. Farmers, ranchers, and residents of these areas seem to have no complaints with the disappearing predators. That is until the prey these predators had been keeping in check trample their gardens, eat their crops, and disease their herds. The prevalent eradication of top predators from ecosystems has agitated the regulatory balance these predators once provided. Our removal of predatory species has eliminated their role of regulating prey species’ populations.

With the incredible shrinking populations of predator species, scientists find them difficult to study. These predators are reduced to fractions of their former habitats and are instinctively secretive; it is not surprising that their sightings are rare. Without ample research subjects, scientists are quick to dismiss studies on predators. However, in studying their absence, we can still draw very important conclusions about these species.

One such conclusion is that the loss of top predators world-wide has upset the biodiversity of many ecosystems. Biodiversity is the balance between all organisms occupying an ecological community. Varied vegetation, herbivore grazing, and predation all play important roles in maintaining biodiversity in each

Top predators are essential to

the integrity of ecological

communit ies… it is imperative

to retain or restore top

predators to as many parts of

North America as pract ical… Terborgh, et al.

ecosystem. To understand why each element is so crucial to biodiversity, let’s recall the food chain. Every living organism in an ecosystem supports other living organisms. For example, in Figure 1 the vegetation supports the rabbit. The rabbit in turn supports the wolf. The wolf, after dying, is turned into necessary nutrients in the soil that will support the growth of more vegetation. This is a minimal representation; food chains are in actuality much more complex and usually compound into a food web (as each organism relies on more than one source for its survival). However, as you can see from this simple depiction, removing one any single element will interrupt the life-supporting role and the balance in which each element regulates the other elements. This is called a trophic cascade.

Figure 1

More on Trophic Cascades

The standard definition of

trophic is “of or relating to

nutrition.” Each level of the food

chain is a trophic level. A trophic

cascade is where different levels

of the food chain or web are

affected by the loss or addition of

another element. To see exactly

how trophic cascades work, visit:

http://youtube.com/watch?

v=O8BV0VCn1JU for a short

video.

We can find trophic cascades in both top-down and bottom-up processes at work in ecosystems. “Top-down” stems from the levels of the tropic chain (i.e., the food chain) being manipulated from the top of the chain down. To expand on this, return to our previous example. Removing the wolf from the simple food chain would allow the rabbit to overpopulate (as rabbits are known to do). As a result, the vegetation the rabbit population survives on would suffer, unable to keep up with the increase of its superior trophic level’s increase. The opposite of this effect is true in bottom-up processes. If we were to increase the number of plants available, this too could cause the rabbit population, and thus the wolf population, to amplify. Trophic cascades are being recognized in national parks across America; one such example has been documented in The Journal of Biological Conservation, remarking on the loss of cougars in Zion National Park. Professor Robert Beschta of Oregon State University states, “When park development caused cougars to begin leaving Zion Canyon in the 1930s, it allowed much higher levels of deer browsing. 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 same effect has been noted in Yellowstone National Park (as demonstrated in the video linked below) with the removal of wolves and the dramatic increase in the number of elks. The amazing factor not yet considered is how these trophic cascades work in detriment to the species whose numbers explode. They quickly diminish their own resources, resources that also support other species. To explain, think of the food supply that both white-tailed deer and rabbits rely on. With the elimination of the white-tailed deer’s main predator, the deer will begin to consume more of the food supply. Rabbits, in turn, are then left with less food and their population decreases. This cause-and-effect action is known as the “Paine effect.” Through the Paine effect, we can determine that removing the top predator of an ecosystem results in loss of diversity of the prey community; again, we can conclude that top predators are absolutely crucial to maintaining biodiversity (which is essential for all species’ survival). Reviewing multiple ecosystems around the globe supports this conclusion. One such example was

herbivores onto predator-free islands by sailors centuries ago to ensure a food supply upon successive visits. Without any natural predators to control the number of herbivores, the plant-eaters destroyed the vegetation of the islands. On islands like Ascension, Juan Fernandez, the California Channel Islands, and St. George Island, the herbivores’ destruction of the existing plant-life lead to their own downfall, as they now had no resources on which to survive.

In the modern era, humans are responsible for the missing top predators. In their absence, we are noticing an explosion of their

Mammals that would have been

part of the prey pool of missing

carnivores, such as wolves and

cougars, have become notoriously

abundant to the point that some of

them are now nuisances: by being

road hazards, by browsing

ornamental shrubbery, by raiding

trashcans, by preying on birds and

their nests, by destroying vegetable

gardens, and by flooding people’s

yards. Terborgh, et al.

former prey. Prey species’ populations expanding have caused a noticeable amount of problems for humans. Deer-related car accidents number into the thousands annually; moose, too, stray into highways at their active times, which happens after dark when drivers’ visibility is already reduced. Raccoons and opossums are just as responsible for overturned trashcans as stray dogs; beavers, misplaced from their natural territories and without predators to keep their numbers in check, build dams in the most inconvenient places flooding residential yards. As frustrating as each of these situations may be, people have no where to place the blame outside of our own species. Our reduction of natural habitats and elimination of natural predators has led to the complications we are now experiencing, all a product of the loss of biodiversity. We have also been known to upset biodiversity by introducing predators into areas previously devoid of predators. When the brown tree snake was introduced and took up residence in Guam, it flourished. Consequently, the native bird population drastically decreased. With the reintroduction of the gray wolf in the northern Midwest area of the United States,

caribou, elk, deer, and moose populations have declined. While these examples have not been controlled experiments and not always carefully monitored, their results are consistent. Human interference in nature’s design, specifically the intricate roles of the trophic ladder, typically produces negative reactions throughout the ecosystem for all species involved.

As more and more environmental issues appear on the screens of our televisions, the front pages of our newspapers, and in the headlines of our favorite online news, we cannot escape the importance of conserving nature. A top concern for conservationists is maintaining biodiversity; one guaranteed way to destabilize an ecosystem is by removing the top predators from it. Their removal causes a chain reaction; first, we see an overabundance of targeted prey. This consequently affects other species who consume the same food as the now overabundant species. It also disrupts and destroys vegetation and habitats in the ecosystem. There is hope...

The conclusion that top

predators play a major

regulatory role seems

inescapable. Terborgh, et al.

More on Ecosystems An ecosystem is an interconnected community of

living organisms and the physical environment in

which they interact to form a life-support system.

You don’t have to travel to Yellowstone or a state

park to witness an ecosystem at work; you can see

one in your own backyard! Discovery Channel’s

Animal Planet hosts a show, Backyard Habitat,

which assists families with developing ecosystems at

their homes. Visit: http://animal.discovery.com/

fansites/backyard/backyard.html for example

habitats, tips on renovating your own yard, or to see

how to have your yard certified through the National

Wildlife Federation.

Despite the gray wolf’s protected status as an Endangered Species and the proven need for the cougar in maintaining balance within ecosystems, both are legally hunted within several states (Cougars are currently not on the Threatened or Endangered Species lists; however, their sightings are so rare there is no national or state-specific count of the remaining cats in the wild). At this time, though, there are groups working to limit and hopefully, eventually remove these species from open-game lists. They propose that with the right management plans and some considerations for residents living in or near these predator habitats, both humans and predators can live in harmony.

You can take part in their valiant efforts to save and protect these top predators. With your vote, your time, your contributions, your consideration, you can help maintain biodiversity in the ecosystems across the United States.

The answer to the opening question remains without a single, conclusive answer. Many factors contribute to the loss of species. However, some factors we can control. We must take direct action to restoring and maintaining top predators because their irreplaceable and critical roles inside ecosystems affects practically every other organism dependant upon that ecosystem. We are part of their ecosystems. In addition to visiting your state’s official website for more information on protecting the predator species in your state, please review the list of conservation groups’ website included to the right. Each offer many ways you can help in the plight to rescue, restore, and maintain top predators in the United States and internationally.

To prevent ecosystems all

over North America from

experiencing convulsions

brought about by trophic

cascades, the full spectrum of

ecological processes that

operates to perpetuate

biodiversity, especially

predat ion, must be widely

maintained. Terborgh, et al.

Article composed by Stacia Clayton. Materials derived from “The Role of Top Carnivores in Regulating Terrestrial Ecosystem” by Terborgh, John; Estes, James; Paquet, Paul; Ralls, Katherine; Boyd-Heger, Diane; Miller, Brian; and Noss, Reed.

For more information:

• Keystone Conservat ion • http://www.keystoneconservation.us

• Center for Biological Diversity • http://www.biologicaldiversity.org

• Mountain Lion Foundation • http://www.mountainlion.org

• Wildlife Rescue & Rehabilitat ion, Inc. • http://www.wildlife-rescue.org

• Wolf Conservat ion Center • http://host148.ipowerweb.com/~nywolfor

• Conservat ion Northwest • http://www.conservationnw.org

• Internat ional Wolf Center • http://www.wolf.org

• Defenders of Wildlife • http://www.defenders.org