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How the Earthquake Bird Got Its Name and Other Tales of an Unbalanced Nature
By H.H. Shugart
Yale University PressCopyright © 2007 Yale University Press
All right reserved.
What, is the jay more precious than the lark, Because his feathers are more beautiful? Or is the adder better than the eel, Because his painted skin contents the eye? -Petruchio in act 4, scene 3 of "The Taming of the Shrew" William Shakespeare (written circa 1594)
Petruchio's dilemma is our dilemma as well. We choose whether the adder is better than the eel: in the decisions we make that alter the planet's environment, we favor some species and disfavor others. Intentionally or unintentionally, we manage the biota and the environment of our planet. Our decisions have eliminated some species and created the opportunities and environments for others to become pests.
However, our challenge is more complex than deciding which species to favor in our planetary management. In a changing and interactive world, we are unable to do only a single thing; the interactions in ecosystems cause one change to produce another change and yet another. The question is how far these may carry forward in a progression of additional changes.
In times past, the seeming connectedness of natural systems madescientifically inclined intellectuals see the universe as a well-assembled clock. The wonderful interaction between form and functioning that was obvious in the natural history of plants and animals eventually implied that extinction of species was not included in the workings of nature. The world seemed part of an intricate clockwork universe. Nature appeared to work very well; indeed, it functioned as a clock built by a divine clockmaker. A clock with missing parts does not work; natural systems do work. Therefore, natural systems must not have any missing pieces and extinction must be unnatural.
This view is embedded in Thomas Jefferson's description of the fossil bones of a gigantic ground sloth that he found and named the megalonyx. Because of its large claws, he took the fossils to be those of some sort of oversized carnivore (megalonyx [??] large + lion). Jefferson felt that the megalonyx was still alive somewhere in North America and reasoned: "The bones exist: therefore the animal has existed. The movements of nature are in a never-ending cycle. The animal species which has once been put into a train of motion, is probably still moving in that train. For if one link in nature's chain be lost, another and another might be lost, till this whole system of things should evanish by piecemeal ... If this animal has once existed, it is probable that ... he still exists." When Lewis and Clark were sent to explore the Louisiana Purchase in 1803, President Jefferson instructed them to watch for and report on large beasts such as the megalonyx, which he thought likely were alive somewhere in the American West. Unfortunately, the megalonyx and a remarkable diversity of other large mammals that were its contemporaries were already extinct.
Jefferson's clockwork universe theme is echoed today by familiar phrases such as "the balance of nature," "the wilderness concept," or "the virgin forest" and "the unspoiled prairie." We manage parks, nature reserves and conservation preserves with these concepts as the foundation of our actions. The objective of this book is to provide an alternative view, to give insights into the dynamically changing nature of ecosystems and the implications of this dynamism for our stewardship of the planet.
Extinction of species is a part of the Earth's biological history. Since higher forms of life evolved, periodic catastrophes have been associated with mass extinctions. Nine such extinctions may have occurred in two combined cycles. While the topic is hotly debated, these cycles conform to large changes on the Earth's surface (volcanic eruptions and other tectonic events, sea-level changes, reversals in the magnetic poles) and evidence of prehistoric meteor impacts. These cataclysmic events may derive their periodic nature from the movement of our solar system with respect to the plane of the Milky Way galaxy. One of these cycles has extinctions occurring every 33 million years or so; it is combined with a longer cycle occurring every 260 million years.
The largest extinction "event" occurred 245 million years ago (in the Permian period), when marine animal families dropped by more than 50 percent and the number of known genera was reduced by around 80 percent. Such drops in the existence of genera imply even higher losses of species, perhaps as much as 96 percent. Another extinction, better known to many, occurred at the end of the Cretaceous period, 65 million years ago. Often called the "End of the Age of Dinosaurs," it involved the extinction of approximately half of the living genera: many kinds of microscopic aquatic plants and animals, marine and flying reptiles, and dinosaurs. However, land plants, crocodiles, snakes, mammals and many kinds of invertebrates survived these mass extinctions. There are (and likely will continue to be) differences of opinion as to the cause; an asteroid impact or violent volcanic eruptions have been suggested as possible suspects.
We know that extinctions do occur, sometimes on an incredible scale. We are still trying to understand whether or not ecosystems behave more or less similarly when the diversity of species is altered. With enough extinctions, does the whole system, "evanish by piecemeal"? The relation between the species richness of ecological systems and the large-scale performance of these ecosystems is difficult to study. Given how little we know, we have produced a remarkable volume of speculation about the connections.
One might argue that in such a dynamic world any extinction that could substantially alter ecosystems should have already done so. In a world of extinctions and periodic cataclysms, only the "tough" ecosystems remain. However, technologically advanced, industrial human societies create novel perturbations outside the realm of conditions experienced in the history of most terrestrial ecosystems. Humans transport and introduce new species, alter the patterns of disturbance and baseline conditions, and change the configurations of landscapes.
The effect on the environment and the biota of industrial societies at high population densities has been profound. Inasmuch as five of the great extinction events may have been due to asteroid impacts with the Earth, the actions of industrial human society have been likened to a "sixth asteroid"-because the high level of species extinctions over the past few hundred years has been caused mainly by human alteration of the planet.
Change is an essential part of nature. Few, if any, observations of ecological systems have displayed long-term constancy. Change in one part of an ecosystem potentially transmits change to another. Animals can alter the vegetation; altered vegetation changes the quality of habitat for animals. This feedback modifies the diversity of animals, which can in turn alter the animals' impact on the environment, and so on and so on.
Human activities, along with variations in the natural environment, inevitably initiate global and regional change. We need to understand where these changes will take us. A basic question is whether or not the magnitude of these changes-iterated through ecosystem feedback-decreases, as do the ripples when a rock is thrown in a pond. Or whether the ripples are amplified into waves, small changes becoming larger over time. We need to know which is the case.
Excerpted from How the Earthquake Bird Got Its Name and Other Tales of an Unbalanced Nature by H.H. Shugart Copyright © 2007 by Yale University Press . Excerpted by permission.
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