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Chapter 5. Natural Systems Under Stress: Disappearing Plants and Animals
The archeological record shows five great extinctions since life began, each representing an evolutionary setback, a wholesale impoverishment of life on earth. The last of these mass extinctions occurred some 65 million years ago, quite possibly because an asteroid collided with our planet, spewing vast amounts of dust and debris into the atmosphere. The resultant abrupt cooling obliterated the dinosaurs and at least one fifth of all other extant life forms. 71
We are now in the early stage of the sixth great extinction. Unlike previous extinction events, which were caused by natural phenomena, this one is of human origin. For the first time in the earth’s long history, one species has evolved, if that is the right word, to where it can eradicate much of life.
As various life forms disappear, they diminish the services provided by nature, such as pollination, seed dispersal, insect control, and nutrient cycling. This loss of species is weakening the web of life, and if it continues it could tear huge gaps in its fabric, leading to irreversible changes in the earth’s ecosystem.
Species of all kinds are threatened by habitat destruction, principally through the loss of tropical rainforests. As we burn off the Amazon rainforest, we are in effect burning one of the great repositories of genetic information. Our descendents may one day view the wholesale burning of this genetic library much as we view the burning of the library in Alexandria in 48 bc.
Habitat alteration from rising temperatures, chemical pollution, or the introduction of exotic species can also decimate both plant and animal species. As human population grows, the number of species with which we share the planet shrinks. We cannot separate our fate from that of all life on the earth. If the rich diversity of life that we inherited is continually impoverished, eventually we will be impoverished as well. 72
The share of birds, mammals, and fish that are vulnerable or in immediate danger of extinction is now measured in double digits: 12 percent of the world’s nearly 10,000 bird species; 23 percent of the world’s 4,776 mammal species; and 46 percent of the fish species analyzed. 73
Among mammals, the 240 known species of primates other than humans are most at risk. The World Conservation Union–IUCN reports that nearly half of these species are threatened with extinction. Some 95 of the world’s primate species live in Brazil, where habitat destruction poses a particular threat. Hunting, too, is a threat, particularly in West and Central Africa, where the deteriorating food situation and newly constructed logging roads are combining to create a lively market for “bushmeat.” 74
The bonobos of West Africa, great apes that are smaller than the chimpanzees of East Africa, may be our closest living relative both genetically and in social behavior. But this is not saving them from the bushmeat trade or the destruction of their habitat by loggers. Concentrated in the dense forest of the Democratic Republic of the Congo, their numbers fell from an estimated 100,000 in 1980 to only 3,000 today. In one human generation, 97 percent of the bonobos have disappeared. 75
Birds, because of their high visibility, are a useful indicator of the diversity of life. Of the 9,775 known bird species, roughly 70 percent are declining in number. Of these, an estimated 1,212 species are in imminent danger of extinction. Habitat loss and degradation affect 86 percent of all threatened bird species. For example, 61 bird species have become locally extinct with the extensive loss of lowland rainforest in Singapore. Some once-abundant species may have already dwindled to the point of no return. The great bustard, once widespread in Pakistan and surrounding countries, is being hunted to extinction. Ten of the world’s 17 species of penguins are threatened or endangered, potential victims of global warming. Stanford University biologist Çagan Sekercioglu, who led a separate study on the status of the world’s birds said, “We are changing the world so much that even birds cannot adapt.” 76
A particularly disturbing recent event is the precipitous decline in the populations of Britain’s most popular songbirds. Within the last 30 years the populations of well-known species such as the willow warbler, the song thrush, and the spotted flycatcher have fallen 50–80 percent; no one seems to know why, although there is speculation that habitat destruction and pesticides may be playing a role. Without knowing the source of the decline, it is difficult to take actions that will arrest the plunge in numbers. 77
The threat to fish may be the greatest of all. The principal causes are overfishing, water pollution, and the excessive extraction of water from rivers and other freshwater ecosystems. An estimated 37 percent of the fish species that once inhabited the lakes and streams of North America are either extinct or in jeopardy. Ten North American freshwater fish species have disappeared during the last decade. In semiarid regions of Mexico, 68 percent of native and endemic fish species have disappeared. The situation may be even worse in Europe, where some 80 species of freshwater fish out of a total of 193 are threatened, endangered, or of special concern. Two thirds of the 94 fish species in South Africa need special protection to avoid extinction. 78
The leatherback turtle, one of the most ancient animal species, and one that can reach a weight of 360 kilograms (800 pounds), also is fast disappearing. Its numbers dropped from 115,000 in 1982 to 34,500 in 1996. At the Playa Grande nesting colony on Costa Rica’s west coast, the number of nesting females dropped from 1,367 in 1989 to 117 in 1999. Writing in Nature, James Spotila and colleagues warn that “if these turtles are to be saved, immediate action is needed to minimize mortality through fishing and to maximize hatchling production.” 79
A World Resources Institute report on coral reefs in the Caribbean notes that 35 percent of Caribbean reefs are threatened by sewage discharge, water-based sediment, and pollution from fertilizer and that 15 percent are threatened by pollution from cruise ship discharges. In economic terms, the Caribbean coral reefs supply goods and services worth at least $3.1 billion per year. 80
The spectacular coral reefs of the Red Sea, some of the most strikingly beautiful reefs anywhere, are facing extinction due to destructive fishing practices, dredging, sedimentation, and sewage discharge. Anything that reduces sunlight penetration in the sea impairs the growth of corals, leading to die-off. Coral reefs play an important role as nurseries for many forms of sea life, including numerous commercial species of fish. 81
One of the fastest-growing threats to the diversity of plant and animal life today is the extraordinary agricultural expansion now under way in Brazil as land is cleared to plant soybeans and, more recently, to produce sugarcane for ethanol. Farmers and ranchers are opening up vast areas in the Amazon basin and in the cerrado, a Europe-sized savanna-like region south of the Amazon basin. Although there are mechanisms in place that are designed to protect the rich biological diversity of the Amazon, such as the requirement that landowners clear no more than one fifth of their land, the government lacks enforcement capacity. 82
Like the Amazon, the cerrado is also biologically rich, with thousands of endemic plant and animal species. It contains many large mammals, including the maned wolf, giant armadillo, giant anteater, deer, and several large cats—jaguar, puma, ocelot, and jaguarundi. The cerrado contains 837 species of birds, including the rhea, a cousin of the ostrich, which grows six feet tall. More than 1,000 species of butterflies have been identified. Conservation International reports that the cerrado also contains some 10,000 plant species—at least 4,400 of which are endemic, not found anywhere else. 83
One of the newer worldwide threats to species, and one that is commonly underestimated, is the introduction of alien species, which can alter local habitats and communities, driving native species to extinction. For example, non-native species may be responsible for 30 percent of the threatened bird species on the IUCN Red List. For plants, alien species are implicated in 15 percent of all the listings. 84
Efforts to save wildlife traditionally have centered on the creation of parks or wildlife reserves. Unfortunately, this approach may now be less effective, for if we cannot stabilize climate, there is not an ecosystem on earth that we can save. Everything will change. As the number of species with which we share the planet diminishes, so too does the prospect for our civilization.
In the new world we are entering, protecting the diversity of life on earth is no longer simply a matter of setting aside tracts of land, fencing them, and calling them parks and preserves. Success in this effort depends on stabilizing both climate and population.
On the plus side, we now have more information on the state of the earth and the life on it than ever before. While knowledge is not a substitute for action, it is a prerequisite for saving the earth’s natural systems—and the civilization that they support.
71. David Quammen, “Planet of Weeds,” Harper’s Magazine, October 1998.
72. Species Survival Commission, 2004 IUCN Red List of Threatened Species (Gland, Switzerland, and Cambridge, U.K.: World Conservation Union-IUCN, 2004).
73. Ibid., p. 11.
74. Ibid.; TRAFFIC, Food for Thought: The Utilization of Wild Meat in Eastern and Southern Africa (Cambridge, U.K.: 2000).
75. Danna Harman, “Bonobos’ Threat to Hungry Humans,” Christian Science Monitor, 7 June 2001.
76. Species Survival Commission, op. cit. note 72; “Birds on the IUCN Red List,” Bird Life International, 2005 update, at www.birdlife.org; “Great Indian Bustard Facing Extinction,” India Abroad Daily, 12 February 2001; Cagan Sekercioglu, Gretchen C. Daily, and Paul R. Ehrlich, “Ecosystem Consequences of Bird Declines,” Proceedings of the National Academy of Sciences, vol. 101, no. 52 (28 December 2004).
77. Michael McCarthy, “Mystery of the Silent Woodlands: Scientists Are Baffled as Bird Numbers Plummet,” Independent (London), 25 February 2005; British Trust for Ornithology, “Tough Time for Woodland Birds,” press release (Thetford, Norfolk, U.K.: 25 February 2005); J. A. Thomas et al., “Comparative Losses of British Butterflies, Birds, and Plants and the Global Extinction Crisis,” Science, vol. 303, 19 March 2004, pp. 1,879–81; Dan Vergano, “1 in 10 Bird Species Could Vanish Within 100 Years,” USA Today, 14 December 2004.
78. Janet N. Abramovitz, Imperiled Waters, Impoverished Future: The Decline of Freshwater Ecosystems, Worldwatch Paper 128 (Washington, DC: Worldwatch Institute, March 1996), p. 59; Species Survival Commission, op. cit. note 72, p. 89.
79. James R. Spotila et al., “Pacific Leatherback Turtles Face Extinction,” Nature, vol. 405 (1 June 2000), pp. 529–30; “Leatherback Turtles Threatened,” Washington Post, 5 June 2000.
80. Lauretta Burke and Jonathan Maidens, Reefs at Risk in the Caribbean (Washington DC: WRI, 2004), pp. 12–14, 27–31.
81. Mohammed Kotb et al., “Status of Coral Reefs in the Red Sea and Gulf of Aden in 2004,” in Wilkinson, op. cit. note 63, pp. 137–39.
82. David Kaimowitz et al., Hamburger Connection Fuels Amazon Destruction (Jakarta, Indonesia: Center for International Forestry Research, 2004).
83. Conservation International, “The Brazilian Cerrado,” at www.biodiversityhotspots.org, viewed 10 September 2004.
84. Species Survival Commission, op. cit. note 72, p. 92; Species Survival Commission, op. cit. note 5, p. 28.
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