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by birds of prey that hunted small
ground-dwelling animals such as
mice and voles. In a European
oakwood, that niche would be filled
by Tawny Owls, while on open
grassland Kestrels would fill the role.
Elton also argued that an animal
could not only tolerate a certain set
of environmental conditions, but
could also change them. The tree-
felling and stream-damming
activity of beavers is one of the
most dramatic examples, creating
habitats for fish in dammed pools,
woodpeckers in dead trees, and
dragonflies around pool margins.Niches and competition
British-born zoologist G. Evelyn
Hutchinson, working at Yale
University from the 1950s to the
1970s, examined all the physical,
chemical, and geological processes
at work in ecosystems and
proposed that any organism’s role
in its niche includes how it feeds,
reproduces, finds shelter, andinteracts with other organisms and
with its environment. For example,
each species of trout—and other
fish—has its own range of water
salinity, acidity, and temperature
that it can tolerate, as well as a
range of prey and river- or lake-bed
conditions. This makes some better
competitors than others, depending
on the conditions of the habitat in
which they live. Seen as the father
of modern ecology, Hutchinson
inspired other scientists to explore
how competing animals use their
environment in different ways.
An animal or plant’s niche
width comprises the whole range
of factors it requires to allow it to
thrive. Brown rats, raccoons, and
starlings are examples of animals
with a broad niche width in that
they are able to survive in a wide
variety of conditions. Such species
are called generalists. Other animals
have narrow requirements. ForTHE VARIETY OF LIFE
example, koalas depend almost
entirely on eucalyptus leaves, and
Hyacinth Macaws in the Pantanal
region of Brazil eat virtually nothing
but the hard fruits of two species of
palm trees—these are specialists.
Animals rarely occupy the whole
of their niche width, owing to
competition between species. Part
of the habitat requirement of North
American bluebirds is dead trees
with old woodpecker holes in which
they lay their eggs and raise their
young. Although suitable holes are
common in many forests, bluebirds
cannot occupy all these holes
because they are often out-
competed by more aggressive
starlings. Therefore their realized
niche—the places they actually
occupy—is not as extensive as their
potential (or fundamental) niche.
Many animals share some
aspects of their niche, but not
others. This is called niche ❯❯A true specialist, a koala bear
requires 2.5 lb (1 kg) of eucalyptus
leaves a day. This species is found
in the wild only in Australia, where
eucalyptus is common.Different species press
against one another, like
soap bubbles, crowding
and jostling, as one
species acquires ... some
advantage over another.
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