51
See also: Competitive exclusion principle 52–53 ■ Field experiments 54–55 ■ Optimal foraging theory 66–67
■ Animal ecology 106–113 ■ Niche construction 188–189ECOLOGICAL PROCESSES
habitat known as chaparral, and
how it escaped predators by
running through the underbrush.
The thrasher’s camouflage, short
wings, and strong legs were
perfectly adapted for life in this
environment. Grinnell saw the
chaparral habitat as the thrasher’s
“niche.” His idea also allowed for
“ecological equivalence” in plants
and animals, whereby species
distantly related and living far
apart could show similar
adaptations, such as feeding
habits, in similar niches. In the
Australian outback, for instance,
babbler bird species forage in the
scrubby vegetation in a similar way
to the unrelated thrasher. Grinnell
also identified “vacant” niches—
habitats that a species could
potentially occupy, but where it
was not present.Widening the niche
In the 1920s, ecologist Charles
Elton looked beyond a simple
habitat definition for “niche.” For
him, what an animal ate and what
it was eaten by were the primaryfactors. Thirty years later, George
Evelyn Hutchinson expanded the
definition yet further. He argued
that a niche should take into
account all of an organism’s
interactions with other organisms
and its nonliving environment,
including geology, acidity of soil or
water, nutrient flows, and climate.
Hutchinson’s work encouraged
others to explain the variety of
resources used by a single
organism (niche breadth), the ways
in which competing speciescoexist (niche partitioning), and
the overlap of resources by different
animals and plants (niche overlap).The importance of habitat
Ecological niches depend on the
existence of a stable habitat; small
changes can eradicate niches that
organisms once filled. For example,
dragonfly larvae only develop
within a certain range of water
acidity, chemical composition,
temperature, and prey, and with
a limited number of predators.
The right vegetation is needed by
adult females for egg-laying, and
by larvae for metamorphosis.
The dragonfly also impacts its
environment: its eggs are food for
amphibians; its larvae, which are
both predators and prey, add
nutrients to the water; and the
adults prey on insects. These
requirements and impacts define
its ecological niche. Hutchinson
argued that for a species to persist,
conditions had to be within the
required ranges. If conditions moved
outside the niche requirements, a
species could face extinction. ■An ultra-specialist Giant pandas occupy a very
specialized ecological niche, as
their diet consists mainly of
bamboo. Bamboo is a poor food
source, low in protein and high in
cellulose. Pandas can digest only
a small proportion of what they
eat, which means they have to
eat a lot of bamboo—as much as
28 l b (12.5 kg) each day—and
forage for up to 14 hours a day.
It is unclear why pandas have
become so dependent on bamboo,
but some zoologists suggest it is
because it is an abundant and
reliable food source, and pandas
are not skilled predators.Pandas eat different parts of
bamboo plants according to the
seasons. In late spring, they
prefer the first green shoots.
They eat leaves at other times
of the year, and stems in winter
when little else is available.
Pandas have evolved muscular
jaws and a pseudothumb to
manipulate bamboo stems. Their
digestive tract is inefficient at
processing large quantities of
plant material because it
remains similar to that of its
carnivorous ancestors, although
digestion is helped by the
bacterial fauna in their gut.[A niche] is a highly
abstract multi-
dimensional hyperspace.
George Evelyn
HutchinsonUS_050-051_Ecological_Niches.indd 51 12/11/18 6:24 PM