Erickson1
Kathryn Erickson
Trishia Bailey
English 2010
Report
March 13, 2013
“Predators are, perhaps, something like forest fires--highly controversial, once maligned
as a controllable evil, later understood to be one of the keys to overall forest health” (Insert
reference). Though forest fires are viewed by many as destructive and something that only
destroys everything in its path (which sometimes may be), it is essential to a forest’s health.
Wildfires purge the soil and allow for the regrowth of vegetation within the left-over debris
along the forest floor. This new growth lures in many new species of birds and animals and
allows for the cycle of life to begin again. Without this fearful flame, the environment could not
cleanse itself, and would suffer great consequences. Like forest fires, our predators are generally
viewed in the same fearful light. They are seen as destroyers with wild and untamed natures,
rather than as ushers of new life.
Our predators are more than just something to be feared, they are a crucial key to the
health and balance of the environment. But this balance is being threatened. Global warming
excessive hunting, blind hate, and a lack of understanding to the role that our predators play in
the balance of nature are disturbing and threatening the health of the natural world as we know it.
Such threats to our predators must be controlled or even abolished or else the victims of their
elimination will ultimately be us.
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To simple common sense, the killing of predators may seem like a good thing, especially
if you are raising livestock, however, Joel Berger of the Wildlife Conservation Society argues
that, “The loss of large predators in the wild may be humankind’s most pervasive influence on
nature.” (As quoted by Steve Sautner on wcs.org). The most frightening effect of losing any of
our predators in an ecosystem is not so much that the food chain will be disrupted, as much as
the fact that the complete disappearance of an entire species (especially a predator) can begin a
chain effect that will alter the processes of an ecosystem—a result which can be far more
dangerous to humans (Zielinski).
The scientific term for this “chain effect” is called a trophic cascade. The Britannica
Encyclopedia defines a trophic cascade as, “an ecological phenomenon triggered by the addition
or removal of top predators and involving reciprocal changes in the relative populations of
predator and prey through a food chain, which often results in dramatic changes in ecosystem
structure and nutrient cycling.” (http://www.britannica.com/EBchecked/topic/1669736/trophiccascade).
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James A. Estes and Joel Berger in coordination with a group of other scientists conducted
a study in which they observed the effects of removing apex predators (or top predators) from
nature – a process they called “trophic downgrading.” They discovered that removing the
predators of an ecosystem can have negative effects on other species that reverberate throughout
other associated ecosystems. They followed complex cause and effect relationships and found
that some the unanticipated impacts of the trophic downgrading process included in the increased
dynamics of disease, wildfire, and invasive species. One example that they presented in their
paper described how the reduced numbers of lions and leopards in Africa have led to an increase
in the numbers of olive baboons and also to changes in their behavior, through which they have
had increased contact with people. The
intestinal parasites commonly associated
with the baboons have been found to also
be increasing at a higher rate in the
humans that live in close proximity to
them (Sautner).
Ellen K. Pikitch, another co-author and scientist with Estes and Berger in this study of
“trophic downgrading,” said that apex consumers (which include animals such as big cats,
wolves, sharks, and great whales) are not adaptable to laboratory experiments and because of
this, the effects of removing them from an ecosystem are not easy to document. The findings of
these scientists conclude that, “trophic downgrading—the ecological consequences of losing
large apex consumers from nature – causes extensive cascading effects in ecosystems worldwide,
especially when exacerbated by factors such as land use practices, climate changes, habitat loss,
and pollution” (Stony Brook University ScienceDaily).
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Though finding examples of ecosystems that have experienced “trophic downgrading”
are rare, they do exist. One such example is the result of the construction of one of South
America’s largest man-made lakes: Lake Guri, in Venezuela. This project has been deemed an
“ecologic disaster” because after its completion in 1986, it had raised the water level of the
original Caroni River by over 390 feet. It rose another 164 feet over the following year, making
thousands of islands out of the surrounding
hilltops. John Terborgh, professor of
environmental science at Duke University in
Durham, North Carolina, studied the effects
that Lake Guri had on the surrounding
ecosystem. He found that predators such as
pumas, jaguars, anacondas, eagles, armadillos,
and some weasels were not able to survive on islands that were smaller than 37 acres. Some of
these animals swam or flew away from the island, while others starved to death. With the mass
exodus of these predators, populations of howler monkeys, iguanas, and leaf-cutting ants
exploded. These booming populations resulted in the devastation of island vegetation. Said
Terborgh, “The impact of massive herbivory [plant eating] was to increase the mortality of trees,
especially small saplings…Our model showed very dramatically that the vegetation [on the
islands in Lake Guri] is in a state of collapse." (Stefan Lovgren, National Geographic).
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Another living example of an ecosystem that has experienced “trophic downgrading” is
in our very own Yellowstone National Park with the loss, and later the return of the wolves.
Stefan Lovgren of the National Geographic noted a connection between the disappearance of
aspens and willows in the park with
the elimination of the wolves in
1930. He suggests, based on research,
that the elimination of Yellowstone’s
wolves allowed elk, one of their main
prey animals, to browse aspen and
willow trees without restraint. As a
result, trees and streamside vegetation
disappeared, also leading to the
disappearance of beaver habitat.
Since the return of wolves in 1995,
aspen and willow have started
growing again and a few beavers
have returned to the park (Lovgren).
While the effects that trophic cascades might have on humankind may hold the most
weight of concern in our efforts to preserve the natural predators of the earth’s ecosystems,
another reason to preserve them lies in the fact that once they are gone, they’re gone. There is no
bringing them back.
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Imagine the forever-silence of the world at night without the musical howl a wolf, or the
arctic tundra without the polar bear, or Yellowstone’s Bear Country without the bear, or the
many oceans without the sharks or great whales! While these creatures are at the top of the food
chain in their ecosystems, they are in danger of
forever disappearing from our futures unless
we strive to protect the world that they live in.
If we allow them disappear, we will sentence
the natural process of our world to a fate that
we cannot predict. The true effects of such
losses would not become known to us until
years or decades after it was too late. In the words of Joel Berger, “If we continue with business
as usual and lack an on-the-ground presence to reverse the alarming trends, we continue down a
path of repeating history, one mistake at a time, rather than benefitting from past mistakes”
(Sautner). Let us follow this council to learn from the mistakes of the past and prevent the
dousing of the flame of our forests—the earth’s natural predators.
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Works Cited: