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, most likely when 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. 76
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. One of the leading threats to the earth’s biodiversity is 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 descendants 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 the human population grows, the number of species with which we share the planet shrinks. Yet 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.
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; 20 percent of the world’s 5,416 mammal species; and 39 percent of the fish species analyzed. 77
Among mammals, the 296 known species of primates other than humans are most at risk. The World Conservation Union-IUCN reports that 114 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.” 78
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 connection 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, a failing state with a prolonged civil conflict, their numbers fell from an estimated 100,000 in 1980 to as few as 10,000 today. In one human generation, 90 percent of the bonobos have disappeared. 79
Birds, because of their high visibility, are a useful indicator of the diversity of life. Of the 9,817 known bird species, roughly 70 percent are declining in number. Of these, an estimated 1,217 species are in imminent danger of extinction. Habitat loss and degradation affect 91 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 study on the status of the world’s birds said, “We are changing the world so much that even birds cannot adapt.” 80
Particularly disturbing is the recent 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. 81
Another decline, which began in late 2006 and had direct economic consequences, is that of the honeybee, the principal pollinator of U.S. fruit and vegetable crops. A survey of U.S. beekeepers, conducted from September 2006 to March 2007 by the Apiary Inspectors of America, found that the bees in nearly one quarter of U.S. bee colonies had simply disappeared as a result of what scientists are calling “colony collapse disorder.” Large numbers of colonies have suffered the same fate in Europe, Brazil, and Guatemala. 82
Scientists are baffled by what the French have labeled “mad bee disease.” Bees leaving their hives on pollination forays apparently become disoriented and never return. The principal suspect at this writing is the Israeli acute paralysis virus, which may have originated in Australia. If scientists cannot quickly diagnose this bee malady and devise preventive measures, the world could face an unprecedented disruption of fruit and vegetable production. 83
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 65 percent of the fish species evaluated by IUCN that once inhabited the lakes and streams of North America are either extinct or in jeopardy. In Europe, some 109 species of freshwater fish out of the 265 that were evaluated are threatened, endangered, or of special concern. One third of the 97 fish species in South Africa need special protection to avoid extinction. 84
The leatherback turtle, one of the most ancient animals, which 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 and Playa Langosta nesting colonies on Costa Rica’s west coast, the number of nesting females dropped from 1,504 in 1989 to 62 in 2003, then rose slightly to 174 in 2004. 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.” 85
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 graze cattle, plant soybeans, and, more recently, 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 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. 86
Like the Amazon, the cerrado is biologically rich, home to many large mammals, including the maned wolf, giant armadillo, giant anteater, deer, and several large cats—jaguar, puma, ocelot, and jaguarundi. The cerrado contains 607 species of birds, including the rhea, a cousin of the ostrich, which grows up to five feet tall. An estimated 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. 87
Another worldwide threat to species, and one that is commonly underestimated, is the introduction of non-native species, which can alter local habitats and communities, driving native species to extinction. For example, non-native species may be responsible for 29 percent of the threatened bird species on the IUCN Red List. For plants, alien species are implicated in 5 percent of all the listings. 88
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.
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 off, and calling them parks and preserves. Success in this effort depends also 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.
76. David Quammen, “Planet of Weeds,” Harper’s Magazine, October 1998.
77. Species Survival Commission, 2007 IUCN Red List of Threatened Species, at www.iucnredlist.org, updated 12 September 2007.
78. Ibid.; TRAFFIC, Food for Thought: The Utilization of Wild Meat in Eastern and Southern Africa (Cambridge, U.K.: 2000).
79. Danna Harman, “Bonobos’ Threat: Hungry Humans,” Christian Science Monitor, 7 June 2001; “Video: New Bonobo Ape Population Discovered,” National Geographic News, 6 March 2007.
80. Species Survival Commission, op. cit. note 77; “Great Indian Bustard Facing Extinction,” India Abroad Daily, 12 February 2001; Çagan 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).
81. 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. 1879–81.
82. Dennis Van Engelsdorp et al., “An Estimate of Managed Colony Losses in the Winter of 2006–2007: A Report Commissioned by the Apiary Inspectors of America,” American Bee Journal (July 2007), pp. 599–603; Alexei Barrionuevo, “Bees Vanish, and Scientists Race for Reasons,” New York Times, 24 April 2007.
83. Joel Garreau, “Honey, I’m Gone,” Washington Post, 1 June 2007; Erik Stokstad, “Puzzling Decline of U.S. Bees Linked to Virus from Australia,” Science, vol. 317, issue 5843 (7 September 2007), pp. 1304–05.
84. Species Survival Commission, 2004 IUCN Red List of Threatened Species (Gland, Switzerland, and Cambridge, U.K.: IUCN, 2004), p. 89; Species Survival Commission, op. cit. note 77.
85. 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; Pilar Santidrián Tomillo et al., “Reassessment of the Leatherback Turtle (Dermochelys coriacea) Nesting Population at Parque Nacional Marino Las Baulas, Costa Rica: Effects of Conservation Efforts,” Chelonian Conservation and Biology, vol. 6, no. 1 (2007), pp. 54–62.
86. David Kaimowitz et al., Hamburger Connection Fuels Amazon Destruction (Jakarta, Indonesia: Center for International Forestry Research, 2004).
87. Conservation International, “The Brazilian Cerrado,” at www.bio diversityhotspots.org, viewed 19 July 2007; Center for Applied Biodiversity Science, “Hotspots Revisited: Cerrado,” at www.biodiversity science.org/publications/hotspots/Cerrado.html, viewed 19 July 2007; butterfly diversity from Helena C. Morais et al., “Caterpillar Seasonality in a Central Brazilian Cerrado,” Revista de Biología Tropical, vol. 47, no. 4 (1999), pp. 1025–33.
88. Species Survival Commission, op. cit. note 77.
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