Lessons in Extinction 2
Contents Updated: Monday, September 13, 1999
Rates of Extinction
Civilization does not seem to alter us. Quite the opposite! Humans have savagely hunted down the animals with which they share the globe since they discovered technical ways of compensating for their puny bodies. In historic times humans have exterminated many varieties of animals and birds, though some of them, like the bison, existed in vast numbers.
Myers highlights the rapidly increasing rate of destruction as technology has improved:
As a primitive hunter, man proved himself capable of eliminating species. From the year AD 1600, however, he became able, through advancing technology, to over-hunt animals to extinction in just a few years.
The rate of extinction of species of mammals and birds (not counting lesser creatures and plants) increased from one every four years from 1600 to 1900 AD to one every year in most of the present century. By 1974 writers in Science magazine considered that 1000 species of all kinds were becoming extinct every year. If the tropical forests are substantially cleared:
By the end of the century we shall have lost one million species, possibly many more. Except for the barest handful, they will have been eliminated by the hand of man. (Myers)
This compares with estimates of one species every 1000 years during the mass extinction of the dinosaurs, though the latter must be a serious underestimation because very many species existed—and died—without leaving any remains. Millions of creepy crawlies must have died without trace—and plants. And, for those we do know about, there must also be some degree of averaging over a long time period of much more sudden extinction events because of the generally poor resolution of time in old rocks. When the time resolution is better because deposition was copious, we find that extinction in the Cretaceous could occur extraordinarily rapidly—for some species at least.
J.Smit and J.Hertogen found that there were no significant changes in the deposits of foraminifera species for over 600 feet in the K-T boundary layer, representing millions of years in time, but they disappeared in a fraction of an inch representing about 200 years. Mankind’s ability to kill off marine and aquatic species in bulk has developed since the start of the industrial revolution about 200 years ago.
Imbalance of Biomass
In addition to the wanton destruction of species, human proliferation has created a huge imbalance in faunal variety illustrated by the huge human biomass of 250 million tons—probably greater than that of any other animal species. And, besides the six billion human animals, there are their domesticated animals—three billion domestic herbivores. What we see is a reduction of species variety together with an increase in actual numbers of some animals. That is just what happened at the end of the Cretaceous.
A large predator will not hunt mice. The reward is not worth the effort. Nor would men be expected to bother with small prey. The pattern of extinctions of mammals in the last million years shows that so far 50 per cent of large mammals have gone but only two per cent of small mammals have. This too is similar to the extinctions at the time of the dinosaurs. But if mankind did not hunt them, why have some small mammals died out?
Effects tend to knock on. Norman Owen Smith of Witwatersrand University in South Africa, has proposed that overhunting, which caused the extinction of the larger herbivores, led also to the loss of open ground. The lack of the herds allowed the bush to grow in to the grasslands again. Since the smaller herbivores, which lacked the size to keep the forests at bay, were also disadvantaged by the spreading bush, they also lost ground and became extinct. Thus although mankind did not hunt the smaller animals his overhunting of the larger ones indirectly caused the downfall of some of the others.
But some opportunistic small species like the sparrow and the rat make a virtue of the environment created by man. The same thing happened in the Cretaceous when birds and some inconspicuous rat-like creatures thrived in the disruption of the environment created by the anthroposaurs, and then survived their demise to colonize the world—the birds and our ancestors, the primitive mammals.
A future student of the rocks, looking back on the terminal extinction at the end of the Tertiary would see extinctions starting much sooner in Europe and Africa than in the Americas. Diversity would seem to continue for longer in South America where man did not arrive until much later.
In the Triassic the dinosaurs of Asiamerica were diverse and abundant but elsewhere they seemed static and conservative. Could that suggest that the primitive but emerging anthroposaur did not get to Asiamerica until late but that his unwelcome attentions held back the evolution of species elsewhere from an earlier time?
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