Predators around the world are facing extinction rates hundreds to thousands of times higher since human introduction. The removal of top predators from ecosystems has disrupted the regulatory balance and decreased biodiversity. Without predators controlling prey populations, prey species multiply rapidly which overtaxes resources and decreases diversity within the prey community through the "Paine effect." Trophic cascades occur when changes in one part of the food chain impact other levels, and they demonstrate the importance of predators in maintaining ecosystem integrity.

1. 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 With the incredible shrinking ecosystem. To understand why
cougar might for a moment populations of predator species, each element is so crucial to
distract you from the glistening scientists find them difficult to biodiversity, let’s recall the food
canines capable of ripping flesh study. These predators are chain.
from bone. Sunning at the zoo, reduced to fractions of their Every living organism in an
these ‘big cats’ hardly appear to former habitats and are ecosystem supports other living
retain their natural predatory instinctively secretive; it is not organisms. For example, in Figure
ways. Here, safely locked away surprising that their sightings are 1 the vegetation supports the
behind thick glass walls, they rare. Without ample research rabbit. The
stimulate our curiosity, our subjects, scientists are quick to rabbit in
interest, even perhaps our desire. dismiss studies on predators. turn
One can be captivated by the However, in studying their supports
power of the majestic, fluid absence, we can still draw very the wolf.
movements of these magnificent important conclusions about these The wolf,
creatures. species. after dying,
Still, this awe and amazement is turned
has done little to aid the cats in into
Top predators are essential to
surviving the onset of humans. necessary
the integrity of ecological
The cougar population, much like nutrients in
that of the gray wolves, has the soil that
communit ies… it is imperative
steadily declined with the will support
to retain or restore top
increase of human populations. the growth
Farmers, ranchers, and residents of more
predators to as many parts of
of these areas seem to have no vegetation.
North America as pract ical…
complaints with the disappearing This is a
predators. That is until the prey minimal Figure 1
Terborgh, et al.
these predators had been keeping representation; food chains are in
in check trample their gardens, actuality much more complex and
eat their crops, and disease their One such conclusion is that the usually compound into a food web
herds. loss of top predators world-wide (as each organism relies on more
The prevalent eradication of has upset the biodiversity of many than one source for its survival).
top predators from ecosystems ecosystems. Biodiversity is the However, as you can see from this
has agitated the regulatory balance between all organisms simple depiction, removing one
balance these predators once occupying an ecological any single element will interrupt
provided. Our removal of community. Varied vegetation, the life-supporting role and the
predatory species has eliminated herbivore grazing, and predation balance in which each element
their role of regulating prey all play important roles in regulates the other elements. This
species’ populations. maintaining biodiversity in each is called a trophic cascade.

2. We can find trophic cascades cottonwoods along the herbivores onto predator-free
in both top-down and bottom-up streambanks and heavy bank islands by sailors centuries ago to
processes at work in ecosystems. erosion…” The same effect has ensure a food supply upon
“Top-down” stems from the levels been noted in Yellowstone National successive visits. Without any
of the tropic chain (i.e., the food Park (as demonstrated in the video natural predators to control the
chain) being manipulated from the linked below) with the removal of number of herbivores, the plant-
top of the chain down. To expand wolves and the dramatic increase eaters destroyed the vegetation of
on this, return to our previous in the number of elks. the islands. On islands like
example. Removing the wolf from The amazing factor not yet Ascension, Juan Fernandez, the
the simple food chain would allow considered is how these trophic California Channel Islands, and St.
the rabbit to overpopulate (as cascades work in detriment to the George Island, the herbivores’
rabbits are known to do). As a species whose numbers explode. destruction of the existing plant-
result, the vegetation the rabbit They quickly diminish their own life lead to their own downfall, as
population survives on would resources, resources that also they now had no resources on
suffer, unable to keep up with the support other species. To explain, which to survive.
increase of its superior trophic think of the food supply that both
white-tailed deer and rabbits rely Mammals that would have been
level’s increase. The opposite of
part of the prey pool of missing
this effect is true in bottom-up on. With the elimination of the
processes. If we were to increase white-tailed deer’s main
carnivores, such as wolves and
the number of plants available, this predator, the deer will begin to
cougars, have become notoriously
too could cause the rabbit consume more of the food
supply. Rabbits, in turn, are then abundant to the point that some of
population, and thus the wolf
population, to amplify. left with less food and their
them are now nuisances: by being
Trophic cascades are being population decreases. This
cause-and-effect action is known road hazards, by browsing
recognized in national parks
across America; one such example as the “Paine effect.” Through ornamental shrubbery, by raiding
has been documented in The the Paine effect, we can
trashcans, by preying on birds and
Journal of Biological Conservation, determine that removing the top
predator of an ecosystem results their nests, by destroying vegetable
remarking on the loss of cougars in
Zion National Park. Professor in loss of diversity of the prey gardens, and by flooding people’s
Robert Beschta of Oregon State community; again, we can
yards.
University states, “When park conclude that top predators are
Terborgh, et al.
development caused cougars to absolutely crucial to maintaining
begin leaving Zion Canyon in the biodiversity (which is essential
1930s, it allowed much higher for all species’ survival). In the modern era, humans are
levels of deer browsing. That set in Reviewing multiple ecosystems responsible for the missing top
motion a long cascade of changes around the globe supports this predators. In their absence, we
that resulted in the loss of most conclusion. One such example was are noticing an explosion of their
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.

3. former prey. Prey species’ caribou, elk, deer, and moose
populations expanding have populations have declined.
caused a noticeable amount While these examples have not
of problems for humans. been controlled experiments
Deer-related car accidents and not always carefully
number into the thousands monitored, their results are
annually; moose, too, stray consistent. Human interference
into highways at their active in nature’s design, specifically
times, which happens after the intricate roles of the trophic
dark when drivers’ visibility is ladder, typically produces
already reduced. Raccoons negative reactions throughout
and opossums are just as the ecosystem for all species
responsible for overturned involved.
trashcans as stray dogs;
The conclusion that top
beavers, misplaced from their
natural territories and without predators play a major
predators to keep their
regulatory role seems
numbers in check, build dams
inescapable.
in the most inconvenient
places flooding residential Terborgh, et al.
yards. As frustrating as each
of these situations may be, As more and more
people have no where to environmental issues appear
place the blame outside of on the screens of our
our own species. Our televisions, the front pages of
reduction of natural habitats our newspapers, and in the
and elimination of natural headlines of our favorite online
predators has led to the news, we cannot escape the
complications we are now importance of conserving
experiencing, all a product of nature. A top concern for
the loss of biodiversity. conservationists is maintaining
We have also been known biodiversity; one guaranteed
to upset biodiversity by way to destabilize an
introducing predators into ecosystem is by removing the
areas previously devoid of top predators from it. Their
predators. When the brown removal causes a chain
tree snake was introduced reaction; first, we see an
and took up residence in overabundance of targeted
Guam, it flourished. prey. This consequently affects
Consequently, the native bird other species who consume the
population drastically same food as the now
decreased. With the overabundant species. It also
reintroduction of the gray disrupts and destroys
wolf in the northern Midwest vegetation and habitats in the
area of the United States, ecosystem. There is hope...
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.

4. For more information:
Despite the gray wolf’s The answer to the opening
protected status as an question remains without a
Endangered Species and the single, conclusive answer.
Keystone Conservation
•
proven need for the cougar in Many factors contribute to the
http://www.keystoneconservation.us
•
maintaining balance within loss of species. However,
ecosystems, both are legally some factors we can control.
hunted within several states We must take direct action to Center for Biological Diversity
•
(Cougars are currently not on restoring and maintaining top
http://www.biologicaldiversity.org
•
the Threatened or predators because their
Endangered Species lists; irreplaceable and critical
Mountain Lion Foundation
however, their sightings are roles inside ecosystems •
so rare there is no national or affects practically every other http://www.mountainlion.org
•
state-specific count of the organism dependant upon
that ecosystem. We are part
remaining cats in the wild).
Wildlife Rescue & Rehabilitation, Inc.
•
of their ecosystems.
At this time, though, there are
http://www.wildlife-rescue.org
groups working to limit and •
hopefully, eventually remove
these species from open- In addition to visiting your
Wolf Conservation Center
•
game lists. They propose that state’s official website for
http://host148.ipowerweb.com/~nywolfor
•
with the right management more information on
plans and some protecting the predator
Conservation Northwest
considerations for residents species in your state, please •
living in or near these review the list of conservation http://www.conservationnw.org
•
predator habitats, both groups’ website included to
humans and predators can the right. Each offer many
International Wolf Center
•
live in harmony. ways you can help in the
http://www.wolf.org
plight to rescue, restore, and •
maintain top predators in the
To prevent ecosystems all United States and Defenders of Wildlife
•
internationally.
over North America from http://www.defenders.org
•
experiencing convulsions
brought about by trophic
cascades, the full spectrum of
ecological processes that
operates to perpetuate
biodiversity, especially
predation, must be widely
maintained.
Terborgh, et al.
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.
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.