|| Some ecologists assert that ecosystem stability is
influenced by species diversity. Roughly speaking, species diversity is
a measure of the number of species living in a community. The higher
the diversity, the greater the stability. Observations that extremely
complex ecosystems, such as tropical rain forests, remain unchanged
almost indefinitely if undisturbed support this idea. Simpler
ecosystems, such as tundra, are less stable, that is, they experience
sudden, drastic shifts in
| population size. Other simplified ecosystems, such as fields
of wheat and corn are also extremely vulnerable to change, and they
deteriorate rapidly if biotic factors shift very much.
To understand why ecologists think there may be
a connection between stability and diversity, consider the food webs in
simple and complex ecosystems. The number of species in a food
web in a mature ecosystem is large. So is the number of
interactions among these organisms. In a complex ecosystem, the
elimination of one species would probably have little effect on the
ecosystem. In sharp contrast, the number of species in the food
web of a simple ecosystem is small. The elimination of one
species could have repercussions on all other species.
In the frozen northern regions of Canada and Alaska, species diversity
is low. Heading south, diversity increases until one reaches the
tropics of Central America, where diversity is highest. The
relationship between latitude is also found in plants and virtually all
other kingdoms. Latitude, therefore, is an important factor
affecting species diversity. The connection between latitude and
species diversity is climate.
| Quite clearly, the milder the climate, the more species live
Simplifying ecosystems by reducing species
diversity makes systems less stable and more vulnerable to outside
influences. Some researchers maintain that populations and
ecosystems rarely, if ever, return to equilibrium once disturbed.
Returning to equilibrium, if possible, would depend in large part on
the nature and severity of the disturbance. Evidence suggests,
that ecosystems can recover from small perturbations, such as changes
in rainfall or short-term drought.
More severe alterations, such as deforestation
of the tropics, may render a system unable to recover.
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