Environmental History

Human interactions with the environment are constantly changing. This is well illustrated by the history of human-wildlife interactions in North America, a continent that has been inhabited by us humans for "only" the past 13,500 years. Our history here is also a brief history of the concepts of nature, wilderness, and wildlife. A discussion of the changes in meaning of these seemingly simple terms highlights the dramatic changes that have occurred in our understanding of the world we live in. The history of these ideas reflects our changing attitudes toward the environment in a broader sense and helps to illuminate how we have gotten ourselves into the present environmental crisis. An understanding of environmental history also provides reasons to think that there is at least some hope we can work our way out of the present crisis with many of our natural systems intact. In order to better delineate such a long period of history, we break the historical record up into somewhat arbitrary "eras" that are borrowed from An Introduction to Wildlife Management by J. H. Shaw (1985). The exact dates for these eras have little meaning by themselves but instead act as indicators of cultural shifts that are largely continuous in nature. This chapter serves as an introduction to the entire book. We introduce ideas, terms and topics that we will revisit many times in the coming chapters. Our goal is to provide a basic understanding of the historic roots of modern conservation biology and of the global environmental crisis.

PRE-EUROPEAN ERA (11,500 BC TO AD 1500)

Humans invaded North America some time during the last ice age, roughly 13,500 years ago, when sea levels were lower and it was presumably possible to walk across the Bering Land Bridge connecting Asia and Alaska. Although evidence is scanty, it appears that once the glaciers melted sufficiently to allow passage out of Alaska, colonizing bands of human beings spread across the continent. Using boats, they apparently moved along the coast, down to the tip of South America, in less than 1,000 years. Even at this early stage of the human invasion, there is evidence to suggest that people had a major impact on their environment and the wildlife with which they lived.

Before humans entered the picture, North America had an impressive assortment of very large mammals and birds. Many members of this group were plant eaters (herbivores) and included elephants (woolly mammoths, giant mammoths, and mastodons), horses, camels, giant bison, giant ground sloths, giant armadillos, tapirs, giant beavers, giant tortoises (roughly the size of a small car), and a giant pig that was as large as the largest boars of Europe. An entire group of now extinct mega-predators preyed on these large herbivores, including cheetahs, saber-toothed tigers, giant wolves, and two species of lion (one larger than the modern lions of Africa). There also existed a truly fearsome short-nosed bear, about twice the size of a modern grizzly bear, which ran down its prey as cheetahs and wolves do today. Jaguars lived far north of their current tropical latitudes, into the forests of Canada, as did many of the New World cats now restricted to Central and South America. There also existed a group of large meat-eating birds, the largest of which were the teratorns, scavenging birds with wingspans up to 5 meters. The endangered California condor is the last remnant of these giant scavenger birds. There was even a giant vampire bat adapted to feeding off the blood of these enormous beasts. So, why isn't North America still home to this wonderful array of creatures?

PLEISTOCENE OVERKILL

The fate of the giants of the past has been the topic of much debate, but considerable evidence supports a hypothesis called "Pleistocene overkill." The idea is that, as humans spread across North and South America, they preyed upon the large herbivores, such as mammoths, ground sloths, and tortoises, and wiped them out. As originally formulated by Paul Martin, the idea was that the large mammals were driven to extinction in a few hundred years in a blitzkrieglike event. A newer version of the hypothesis is that the extinctions were more gradual, based on evidence that, in some areas, humans and large animals coexisted for long periods of time, despite hunting. However, the end result was the same: extinction of the megafauna. Large animals are more vulnerable to extinction than smaller ones because they cannot hide easily from human predators and because they reproduce quite slowly. It is possible that the large animals were also relatively unafraid of human beings, because they would have evolved for hundreds of thousands of years without humans present. In addition, there is some indication that a rapid shift in climate reduced the habitats of many of the giant herbivores, making them more vulnerable to human predation. Likewise, Australian biologist Tim Flannery suggests humans may have changed the environment through their actions, especially by increasing the frequency of fires.

Not unexpectedly, when the large herbivores disappeared, their natural predators, such as saber-toothed tigers and short-nosed bears, became extinct as well. The large scavenger birds, which had adapted to eating the remains of large animals, also followed them into extinction. The California condor may have held on because it had access to the carcasses of large marine mammals such as whales and sea lions, which did not go extinct at this time. The loss of these giant animals also impacted the diversity of smaller animals. Because abundant large animals (such as mammoths and tapirs) alter plant communities by the way they graze, their disappearance would have caused a shift in the plant communities, resulting in the extinction of many smaller species that depended on the habitats maintained by the large grazers. In fact, there existed a grassland ecosystem in Alaska called the mammoth steppe that disappeared entirely once the woolly mammoth went extinct in that region.

The idea of the Pleistocene overkill is quite controversial, yet the principal alternative to explain the rapid loss of all these giant animals is a drastic climate change that occurred with the end of the ice age. Recent fossil data and archeological discoveries increasingly support the idea that the first native peoples were responsible for the extinction of many species.

One of the early groups (but not the first) to colonize North America was the Clovis people. At Clovis...