DO WE MEAN BY EXTINCTION?
February 4, 2007
is a word that will continue to exist, as it has for five centuries. According
to the Oxford English Dictionary, the word was first used in 1432. Like
many commonly used words, "extinct" can be depicted in different
ways, including five fairly discrete categories
and millions of other prehistoric species can be placed in the category
of prehuman extinction, the end-line of natural evolutionary processes,
a condition no human can be blamed for. The next category is that of human-caused
extinctions, such as the passenger pigeon and dodo bird, although no one
alive today can be held accountable.
that existed in our lifetime but is no longer present falls into a third
category--modern extinction. Humans living today can be held responsible,
at least in part, for most modern extinctions. The causes leading to or
hastening modern extinctions include such obvious ones as killing individuals
for sport or commercial harvest. Direct killing and conspicuous forms
of pollution get attention and generate an emotional public reaction,
and global climate change will soon be indicted for some modern extinctions.
But the foremost culprit and continuing threat in regard to modern extinctions
is the destruction of natural habitats.
category is a term I first saw used in the Wall Street Journal--commercially
extinct, which is of course appropriate terminology for a business-oriented
newspaper. A commercially extinct species is no longer economically feasible
to harvest, although the species may be present, even abundant, in some
areas. The Atlantic codfish, once a staple food item in Boston, is now
considered by some experts to be commercially extinct.
category is ecologically extinct. Unfortunately, this is too often the
stage at which we begin to pay attention. Once a species becomes ecologically
extinct, keeping it extant (in existence) requires biological life-support
systems. For example, the California condor was once ecologically extinct,
but U.S. Fish and Wildlife Service programs demonstrated that recovery
is possible. This magnificent species survived for awhile on a human-designed
welfare system, with the young being raised in captivity. Some now roam
free, but their fate is still as precarious as ours would be if were clinging
to a cliff edge in the Grand Canyon.
measure of a species' condition is whether it is extinct or extant. Black
or white. But ecological gray zones of impending extinction should attract
our notice. Is the species declining in its abundance or geographic distribution?
The spotted turtle serves as an example of the problem.
a couple of human generations will go by before the spotted turtle, one
of the prettiest turtles in North America, will be declared a modern extinction.
However, this little black turtle with bright yellow spots on the shell
unquestionably has declined in numbers throughout its range. Two reasons
are apparent, both related to the ecology of the species.
turtles are popular pets, and people who like pet turtles will pay a lot
of money for one. Thus, turtle collectors capture them for the pet trade.
The problem: spotted turtles seldom occur in large numbers in any one
place. Those living in small wetland habitats are often present in low
numbers. The removal of a few dozen adults may effectively eliminate the
population, leading to commercial extinction of the spotted turtle.
assault on spotted turtles comes from habitat destruction. These animals,
like many other wildlife species, depend on wetland habitats. The loss
of small, marshy wetlands means a decrease in the amount of suitable wildlife
habitat. Who can argue that we have fewer spotted turtles now than we
did even two decades ago? We definitely have fewer wetlands. Before long
the spotted turtle will be ecologically extinct.
be concerned about spotted turtles now, before they become commercially,
then ecologically, extinct. Let's deal with how habitat loss and overharvesting
affect their ecology today, so we do not have to institute welfare and
life-support systems tomorrow. The spotted turtle is only one example
of a threatened species. Hundreds of other examples would serve as well.
We aren't going to eliminate the word "extinct" from the world's
vocabulary. But we might limit the number of species to which the term
must be applied.
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