As humans continue to impact the natural
world around them, what are the likely consequences?
As species dwindle and ecosystems grow impoverished, how do
these changes manifest themselves?
At first, very little seems to happen until a threshold is reached, and
then the ecosystem catastrophically collapses.
A metaphor for this effect is that of an airplane where you slowly remove
rivets from its structure.
Initially nothing happens. There
are so many rivets, the loss of a few doesn’t matter.
However, there comes a point where removing more rivets leads to a
crash..
What confounds experts is at what point
does the removal of one species after another lead to collapse.
Nor are they entirely clear on what constitutes a collapse.
Is it when one species, native or alien, comes to dominate
over all others or is it the disappearance
of all life?
Recently another metaphor has arisen,
comparing the removal of species to the removal of threads from a tapestry.
Initially, you can hardly see any change but as time goes on and more
threads are pulled, the tapestry takes on a worn look and in places becomes so
weak that it is apt to tear.
Neither metaphor offers a full
explanation of what happens. Some
systems don’t collapse in a heap but in a continuum of degradation.
In others, humans reweave the tapestry into
patterns suitable to their own needs.
Almost half the land on earth has undergone change from their activity.
Human control over the natural world, in
part essential for so many to survive, has
led to new patterns, which have hastened species extinction and , more often
than not, completely altered the role the affected ecosystem played before its
transformation. In a sense, we are
“simplifying” systems and on a massive scale.
In doing so, we are making these systems more vulnerable and less stable
to outside change.
Diversity plays a critical role in how an
ecosystem responds to new challenges. Natural
occurrences such as drought, flood, fire, and infestation
are far less threatening to an
ecosystem rich in species than an impoverished one.
Diversity also limits the chances that a single species will come to
dominate a system but will be restrained by its other inhabitants.
(This theme was covered in an essay by William Stevens in the New York Times on July 4,2000).
01/08/04 19:22