140
THE WORLD
IS GREEN
TROPHIC CASCADES
S
oon after the end of World
War II, Aldo Leopold, an
ecologist and one of the top
wildlife management experts in the
United States, challenged the view
that wolves should be eradicated
because they threatened livestock.
In A Sand County Almanac, he
wrote of the destructive effect that
removing this top predator would
have on the rest of the ecosystem.
In particular, he said, it would lead
to overgrazing of mountainsides by
deer. Leopold’s view was an early
expression of the idea of trophic
cascades, although he himself did
not use that term.
Predators help keep a balance
in a food web by regulating the
populations of other animals. WhenIN CONTEXT
KEY FIGURE
Nelson Hairston (1917–2008)BEFORE
1949 Aldo Leopold publishes
A Sand County Almanac,
drawing attention to the
ecological impact of hunting
wolves on mountain plant life.AFTER
1961 Lawrence Slobodkin,
an American marine
ecologist, publishes The
Growth and Regulation of
Animal Populations, a key
ecology textbook.1980 Robert Paine describes
the “trophic cascade effect,”
when predators are removed
from an intertidal ecosystem.1995 The reintroduction of
gray wolves to Yellowstone
National Park sets in motion
a series of ecosystem changes.US_140-143_Trophic_cascades.indd 140 12/11/18 6:24 PM