hUMaN iMpaCts oN the Biosphere 487hoW have human activities affected other
species With Which We share the planet?- Population growth and resource overuse have led to widespread
destruction of the habitats where many other species live. - As a result, species are rapidly going extinct.
- A shift to the principle of sustainability is vital if our species is to
thrive and survive.
taKe-Home messaGechains, including bald eagles, brown
pelicans, ospreys, and peregrine
falcons (below). these predators fell
prey to a product of DDt breakdown
that interferes with physiological
processes. the birds produced eggs
with thin, brittle shells—and many of the chick embryos
didn’t survive to hatching time. some species, including
the peregrine falcon, were
facing extinction.
DDt has been banned
in the United states now for
decades, except for limited
applications where public
health is endangered.
populations of peregrine
falcons and other birds
have begun to recover.
even today, however, some
birds lay thin-shelled eggs.
they pick up DDt at their
winter ranges in latin
america, where DDt is still
widely used.25.10 Biological magnification
Wildlife can be harmed and even driven to extinction by the
process called biological magnification. this term refers to
an increase in concentration of a substance in organisms as
it is passed upward through food chains.
an example is the peregrine falcon, which nearly went
extinct as a result of biological magnification of DDt. this
synthetic pesticide was first used in the tropics during World
War ii to kill mosquitoes that carried malaria. later in europe
it helped control body lice that were transmitting a bacterium
that causes typhus. after the war, it seemed like a good idea
to use DDt against agricultural, garden, or forest pests.
DDt can build up in the tissues of animals that come into
contact with it in the air, water, or food. after the war, it began
to move through the global environment, infiltrate food webs,
and affect organisms in ways that no one had predicted. in
cities where DDt was sprayed to control Dutch elm disease,
songbirds started dying. in streams flowing through forests
where DDt was sprayed to control spruce budworms, salmon
started dying. in croplands sprayed to control one kind of
pest, new kinds of pests moved in. DDt was killing off natural
predators that had been keeping pest populations in check.
Much later, side effects of biological magnification
started showing up far from the areas where DDt was
applied. Most devastated were species at the top of foodgovernments and individuals are beginning to embrace
the principle of sustainability. This principle is simple: By
controlling our population growth, using resources wisely,
embracing renewable energy sources, and protecting the
wild places where other species live, we will be taking
steps that help ensure our own survival as well.Figure 25.23 Melting Arctic ice has put polar bears at risk.
These polar bears are checking out a U.S. Navy submarine
in the Arctic Ocean. The bears hunt from ice shelves and
floes, but the ice appears to be melting rapidly due to climate
change. (U.S. Navy photo by Chief Yeoman Alphanso Braggs)
Figure 25.24 Worldwide, sharks are among the animals
increasingly at risk of overexploitation by human enterprises.
(© Fiona Ayerst/Shutterstock.com)David T. Grewcock/Frank Lane Picture Agency/Documentary Value/Corbis
Peregrine falconSCIENCE COMES TO LIFE
biological magnification
An increase in the concen‑
tration of a substance in
organisms as it is passed
upward through food chains.Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).