Did WE Do THAT?
by David Snoeyenbos
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About every 60 to 120 million years, the earth has experienced a catastrophe so severe that 75% to 95%, of the species living at the time became extinct. These mass extinctions have ocurred five times. The first time it slowly wiped out most of the marine organisms-- the land had not yet been occupied. The last mass extinction resulted from the Yucatan giant meteorite impact 65 million years ago. It took out about three-quarters of the species, including the dinosaurs. A few small mammals managed to survive, huddled in crevices until the murk settled, after which they then evolved to become all the present species.
David Quammen, in his essay Planet of Weeds: Tallying the Losses of Earth's Animals and Plants explains why we are on the brink of mass extinction number six. The essay appeared in the Oct., 1998 Harper's Magazine.
For several hundred years we have observed a few isolated species becoming extinct. Examples are the New Zealand moa which went in 1600, the dodo bird in 1680, and the American passenger pigeon in 1880. It was not until the early 1970's that scientific papers started appearing which suggested that the rate of species extinctions may be accelerating rapidly. In the last 20 years this view has grown, to become accepted fact. What is not predictable is is how fast or far-reaching this current extinction process will become. Ecologists Pimm and Brooks at the University of Tennessee expect that 50% of forest birds will be gone in just 50 years. They expect that of all land and marine species , one-half to two-thirds will be lost if present trends continue.
The cause of this impending mass extinction is not an ice age, or a meteorite impact-- it is us. Is it possible that we could bring down this incredibly complex natural world that has taken 650 thousand centuries to evolve? A majority of scientists in this field now think it is not only possible, but either likely or nearly inevitable.
The driving force behind the extinction process is man's unique ability to compete with other species. After a million years of gradual build-up, now in just 200 years our population has exploded from about one to six billion, and is growing at a rate that is expected to nearly double in the next 100 years. The earth cannot support that population and also maintain its present diversity of species. This is what is happening:
Population growth is most extreme in the developing countries in Africa, Asia and Latin America, the low latitudes where biological diversity is greatest. All potentially productive land will need to be used for food production. It will not be possible to maintain large areas for game preserves, natural forest or wetlands if they can be converted to food production. Small protected areas will no doubt remain, but many species don't survive in small areas.
When some species go, they take others with them because of the complicated and essential interactions among the different species. Just one example is the dependence of the Alaska coast eagles on the otter population. The eagles feed on small fish sheltered in the offshore kelp beds, which are a food source for sea urchins, which in turn are a food source for the otters. If the otters decline, sea urchins multiply and consume the kelp beds. With no shelter, the small fish decline, which in turn, cause the eagles to decline.
In addition to destruction of natural habitat, man causes species loss in another big way. By purposely or accidentally introducing new species to areas with no natural competitors, the native species are driven out. The mongoose, introduced to Hawaii to control snakes, has eliminated most ground-nesting birds. English sparrows and starlings crowd out our native birds; tamarisk trees exclude native stream-side trees in our southwest, and purple loosestrife is dominating north-central wetlands.
If man's inadvertent actions cause the extinction of half of all species, will his own species survive? Quammen suggests that we have become one of the strongest survivors on the planet. He quotes David Jablonski, a microevolutionist: "Oh, we've got to be one of the most bomb-proof species on the planet - We're geographically widespread, we have a remarkable reproductive rate, and we are incredibly good at co-opting and monopolizing resources. It would take a really serious effort to wipe out the human species."
So, what will life be like for us, after mass extinction number 6? After the die-off, if technology can provide an adequate diet, clean water and good health, and relative affluence for a much reduced human population, do we really need the other 30,000,000 species?
For those who need to ask, there is probably no answer.
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