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Written to be accessible to any college-level reader, Protecting Life on Earth offers a non-technical, yet comprehensive introduction to the growing field of conservation science. This multifaceted exploration of our current biodiversity crisis delivers vivid examples throughout, including features on some of nature’s most compelling wildlife. Beginning with a brief introduction to environmental history, the text introduces the central concepts of evolution and ecology, and covers several major issues related to the conservation of biodiversity including extinction, climate change, sustainability, conservation law, and invasive species. It also touches on adjacent disciples such as economics and sociology as they relate to conservation. The text even includes practical advice on the decisions we make every day—how we spend our money, where we live and work, what we eat and buy. Throughout, Protecting Life on Earth underscores the ways in which our future is tied to that of Earth’s threatened species, and demonstrates exactly why conservation is so vitally important for us all.
|Publisher:||University of California Press|
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Protecting Life on Earth
An Introduction to the Science of Conservation
By Michael P. Marchetti, Peter B. Moyle
UNIVERSITY OF CALIFORNIA PRESSCopyright © 2010 the Regents of the University of California
All rights reserved.
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?
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 archeological sites, researchers have found distinctive, beautifully made stone spearheads that would have been well suited for killing large herbivores. These same Clovis spearheads have been found imbedded in the skeletons of large animals, which strongly suggests that these animals were hunted by the Clovis people. Clovis culture rapidly spread throughout North America, and then rather abruptly disappeared after about 300 years—a disappearance that seems to coincide with the extinction of many (but not all) of the large animals of interior North America.
Additional support for the overkill idea comes from data from the growth rings of mammoth tusks at the time of the mammoths' extinction, which indicate that the animals were eating well and not experiencing the starvation that would normally accompany climate-driven extinction. Also, many of the extinct species of megafauna had already survived several other glacial climate cycles during the previous 100,000 years, and so presumably they could have survived one more. It is worth noting that a similar event occurred in Australia, with early humans apparently wiping out a suite of giant marsupials, as well on islands throughout the world. If we accept some version of the Pleistocene overkill hypothesis, then we also have to accept the idea that early hunter-gatherer societies were capable of having large and permanent effects on their environment.
DISEASE AND WILDLIFE POPULATIONS
When the first Europeans arrived in North America they were often impressed with the abundance of wildlife. For example, when Daniel Boone brought colonists to settle the Ohio Valley, he led them into a wilderness of large trees, teeming with deer and bear. Two hundred years earlier, however, this same valley had been largely cleared for farms, which were tended by a dense population of native people. The main cause of the disappearance of so many of the First People at the time of European contact was disease.
Disease epidemics are most likely to occur in dense populations of animals or humans because pathogens can spread more easily among individuals and there is a large supply of susceptible hosts for the disease. Not surprisingly, high population densities in urban centers of Europe and Asia supported many nasty communicable diseases, such as smallpox, measles, chicken pox, bubonic plague, malaria, cholera, yellow fever, and influenza. Most Europeans were relatively immune to diseases such measles and smallpox because they had essentially evolved with the diseases, many of which originated in pigs and other livestock. The plagues such as Black Death that periodically swept through Eurasia, killing millions of people, were powerful agents of natural selection (see Chapter 2). When Europeans came to America, they brought these diseases with them; unfortunately, the native peoples had virtually no resistance to the diseases. Smallpox, measles, and other diseases carried by the early explorers, from Columbus onward, rapidly swept through the continent, dramatically reducing Native American populations. Cortez's conquest of Mexico, for example, was greatly hastened by the reduction of the Aztec population by a measles epidemic.
To say that the effect of these illnesses on the population of the Americas was devastating would be an understatement. It has been estimated that, by the end of the seventeenth century, between 70 and 90 percent of First People had died from European-imported diseases. When the native peoples were wiped out, their game species responded by increasing in number. If you remove major predator, such as humans, then prey numbers will increase, at least temporarily. Thus, the first impact of Europeans on wildlife in the Americas was probably to increase wildlife populations through the tremendous and tragic reduction of the populations of indigenous peoples.
BELIEFS AND ATTITUDES TOWARD NATURE AND WILDLIFE
Many of the earliest North American peoples were hunter-gatherers, meaning that they collected most of their food and were often migratory or nomadic in their behavior. Other groups were more sedentary but managed the local landscapes to produce the goods and services they needed, using tools ranging from fire (to favor desirable grasses and shrubs), to irrigation of crops, to regulating the catch of salmon coming up rivers. No matter where the native peoples were on the spectrum of environmental manipulation, they were dependent on understanding the natural world for their survival. This direct dependence on natural ecosystems required an intimate knowledge of the natural world that was often reflected in their beliefs and attitudes toward nature and wildlife. Such peoples commonly viewed themselves as inseparable from the natural ecosystems and wildlife around them. Animals were often regarded as another "kind" of people, or as spirit beings, who could be appealed to for help and protection. Rituals were commonly performed to show respect, gratitude, and reverence for the animal spirits, with the hope of promoting continued harvest success. Other rituals served to influence natural events, such as the coming of rain, or the harvesting of a crop such as acorns, maize, or wild grains.
The belief in magic, ritual, and the intimate fusion of humans with the natural world can be seen in the cultural traditions of many native cultures, as well as in the wonderful portraits of bison, deer, bighorn sheep, salmon, and other animals painted on cliff walls or in caves. As a species, we Homo sapiens have been hunter-gatherers for most of our evolutionary history; in this time, we did not separate nature, wilderness, and wild animals from human culture. Some anthropologists suggest that, as a result of this connection to nature and wilderness, we experience deep-rooted psychological feelings of well-being when we are placed in circumstances that mimic our ancestral environments. Such environments include natural settings (such as forests and prairies) with views of wildlife (or domestic animals), often near water, especially when frequent interactions with close family members are involved.
ERA OF ABUNDANCE (1500–1849)
Early European descriptions of the New World emphasized the incredible abundance of plant and animal life. The Europeans were astounded by the sheer number and variety of fish available. They were left speechless by the flights of passenger pigeons and measured their numbers in the "millions and millions." Accustomed to firewood shortages in England, settlers were delighted by the variety and abundance of trees in the forests. Unfortunately, in the settlers' minds, the new landscape also contained native peoples, even if their populations were in low numbers because of disease epidemics.
When European settlers came into contact with the indigenous peoples of North America, four factors, all of them related to perceptions of animals and nature, allowed them to justify taking from the natives. First, the unsettled areas of the continent were regarded as inhospitable wild areas that were feared and that needed to be tamed to allow them to be used. Thus, conversion of wilderness to farmland and cities was regarded as a good thing.
Second, settlers generally thought that the native people who lived on the land were not using the land properly. They did not "own" the land in the European sense. Because the native urban cultures had largely disappeared, the native peoples the Europeans encountered were largely hunter-gatherers or practitioners of shifting agriculture, meaning that they would clear a field and then move on when the field began to lose its fertility. European farmers, on the other hand, were accustomed to a system in which a person would farm the same piece of land "in perpetuity," regardless of the health or fertility of the soil. Europeans viewed Native Americans, as "lazy," because they engaged "only" in hunting and fishing. Such activities, in Europe, were leisure activities, not integral parts of a cycle of the seasons as they were for most of the First People. It was much easier to justify taking land from people who were lazy, who didn't own the land, and who were not living up to the biblical commandment to subdue the Earth.
Third, the devastation of native peoples by European diseases (when it was recognized at all) was regarded as an act of Providence, favoring the obviously superior European culture. In the wake of depopulation and social chaos, taking "unoccupied" land seemed not only justifiable but prudent.
Finally, Europeans perceived the environment of the New World not as a set of integrated ecosystems but as a collection of commodities. These commodities, in incredible abundance, were apparently free for the taking. In addition, they saw not only the land but the animals and plants that lived on it as private property. Whereas in most hunting and gathering societies an animal belongs to the individual who kills it, in European society, wildlife was owned by the people who owned the land. When Native Americans "sold" land to Europeans, they perceived themselves as merely sharing the use of the land. Europeans perceived themselves as buying the land and everything on it, regardless of the way the land might be used. These ideological and economic differences caused conflict repeatedly and still do to a certain extent. This can be seen in the history of beaver trapping.
THE BEAVER TRADE
The beaver trade was stimulated by the need of the early European colonies to find a commodity that would repay the debts they owed to European merchants. European settlers and traders were quite aware that they were not as efficient as native hunters, so they hired native people to do the hunting for them. As "lazy" as native peoples were perceived to be, Europeans admitted that they were superb hunters and trappers. Traditionally, hunting peoples had traded with agricultural peoples on the southern coast of New England, exchanging maize (corn) for pelts. Europeans inserted themselves into the traditional network, initially using wampum (shell beads) as currency. However, the context was very different: traditional Native American trade had been based on a complex network of kinship and friendship and had primarily been local, from village to village (although some peoples also made long trips for trading purposes, to acquire precious goods such as obsidian or copper). The new trans-Atlantic fur trade stretched over long distances. However, as a result of native populations being dramatically reduced by disease, traditional kinship groups had largely broken down, and the original networks of trade were weakened.
Excerpted from Protecting Life on Earth by Michael P. Marchetti, Peter B. Moyle. Copyright © 2010 the Regents of the University of California. Excerpted by permission of UNIVERSITY OF CALIFORNIA PRESS.
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Table of Contents1. Environmental History
2. Variation, Natural Selection, and Evolution
3. Species: The Basic Unit of Conservation
4. Climate and Global Patterns of Distribution
5. Ecology: Individuals and Populations
6. Ecology: Communities and Ecosystems
7. Biodiversity and Extinction
8. Value, Economics, and the Tragedy of the Commons
9. Conservation Science
10. Conservation and the American Legal System
11. Invasive Species and Conservation
12. Restoration Ecology
13. Conservation in Action
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