Environmental Engineering Reference
In-Depth Information
relationship.
Such relationships are depicted in Fig-
ures 3-10 (p. 42) and 3-16 (p. 47).
At the individual level, members of the prey
species are clearly harmed. At the population level,
predation plays a role in evolution by natural selection.
It can benefit the prey species because predators such
as some shark species (Case Study, p. 113) kill the sick,
weak, aged, and least fit members of a population. The
remaining prey gain better access to food supplies and
avoid excessive population growth. Predation also
helps successful genetic traits to become more domi-
nant in the prey population through natural selection,
which can enhance that species' reproductive success
and long-term survival.
Some people tend to view predators with con-
tempt. When a hawk tries to capture and feed on a rab-
bit, some root for the rabbit. Yet the hawk, like all
predators, is merely trying to get enough food to feed
itself and its young. In doing so, it plays an important
ecological role in controlling rabbit populations.
How Do Predators Increase Their Chances of
Getting a Meal?
Some predators are fast enough to catch their prey,
some hide and lie in wait, and some inject chemicals
to paralyze their prey.
Predators have a variety of methods that help them
capture prey.
Herbivores
can simply walk, swim, or fly
up to the plants they feed on.
Carnivores
feeding on mobile prey have two main
options:
pursuit
and
ambush.
Some, such as the chee-
tah, catch prey by running fast; others, such as the
American bald eagle, fly and have keen eyesight; still
others, such as wolves and African lions, cooperate in
capturing their prey by hunting in packs.
Other predators use
camouflage
—a change in
shape or color—to hide in plain sight and ambush
their prey. For example, praying mantises (Figure 3-1,
right, p. 35) sit in flowers of a similar color and am-
bush visiting insects. White ermines (a type of weasel)
and snowy owls hunt in snow-covered areas. People
camouflage themselves to hunt wild game and use
camouflaged traps to ambush wild game.
Some predators use chemical warfare to attack
their prey. For example, spiders and poisonous snakes
use venom to paralyze their prey and to deter their
predators.
How Do Prey Defend Themselves Against or
Avoid Predators?
Some prey escape their predators or have protective
shells or thorns, some camouflage themselves, and
some use chemicals to repel or poison predators.
Prey species have evolved many ways to avoid preda-
tors, including the ability to run, swim, or fly fast, and a
Figure 6-5
Sharing the wealth:
resource partitioning
of five
species of insect-eating warblers in the spruce forests of Maine.
Each species minimizes competition with the others for food by
spending at least half its feeding time in a distinct portion
(shaded areas) of the spruce trees, and by consuming some-
what different insect species. (After R. H. MacArthur, “Popula-
tion Ecology of Some Warblers in Northeastern Coniferous
Forests,”
Ecology
36 (1958): 533-536.)
