Synergistic Effects and Conclusions

Any one of these threats to biodiversity might not be enough to drive a species to extinction, but combined they may. Around the world, temperate estuaries have been permanently changed by humans. Estuaries, such as the Chesapeake Bay off the coast of Virginia, are severely affected by nutrient pollution from agriculture and sewage runoff. These excess nutrients cause phytoplankton blooms, some of them toxic, which in turn are decreasing or eliminating oxygen from the bottom sediments, making them uninhabitable to marine life. Historical analysis of the sediments reveals that as early as the late eighteenth century, human settlement in the watershed was affecting nutrient loads to the estuary and consequently the type of phytoplankton that was growing. However, sediments were still not experiencing low oxygen conditions, because the bay also had acres of oysters. Oysters could filter the entire bay in a matter of days, removing the excess phytoplankton and maintaining oxygen levels. But humans then began harvesting oysters at increasing rates, until the bay was nearly depleted of oysters by the 1930s. Without oysters to control the impact of excess nutrients from the land, the system collapsed, and the Chesapeake is now substantially and possibly irreversibly altered. That is not the only place where multiple disturbances brought about the collapse of an entire ecosystem. For instance, the Hawaiian Islands harbor one of the earth's most spectacular biotas, but also one of the most fragile and endangered. Introductions of exotic species, in combination with habitat disturbance by humans, have transformed more than 90 percent of the natural areas in Hawaii and led to countless extinctions. In the Amazon region, the water lost from plants through evapotranspiration is believed to contribute 50 percent of the annual rainfall. Deforestation reduces evapotranspiration rates, leading to decreased rainfall, and subsequently increases the area's vulnerability to fire (Laurance and Williamson, 2001). Fire can quickly burn acres of forest. Deforestation thus leads to additional forest loss through its indirect affect on the climate.

Now more than ever, we are realizing that all life on earth is interconnected. Humans are affecting not just the species that will go extinct today but also what will evolve in the future. The future of earth's biodiversity depends on us. As we begin to understand our impact on biodiversity and its importance to human survival, we are also discovering how to save biodiversity.

This material is based upon work supported by the National Science Foundation under Grant No. 0127506. Any opinions, findings and conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

—Melina F. Laverty and Eleanor J. Sterling


Barnes, David K. A. 2002. "Biodiversity: Invasions by Marine Life on Plastic Debris." Nature 416: 808-809; Coe, James M., and Donald B. Rodgers, eds. 1997. "Marine Debris: Sources, Impacts and Solutions." New York: Springer-Verlag; Cox, George W. 1999. Alien Species in North America and Hawaii: Impacts on Natural Ecosystems. Washington, DC: Island; Didham, Raphael K. 1998. "Altered Leaf-litter Decomposition Rates in Tropical Forest Fragments." Oecologia: 397-406; Elton, Charles S. 1958. The Ecology of Invasions by Animals and Plants. London: Methuen; Gascon, Claude, et al. 1999. "Matrix Habitat and Species Persistence in Tropical Forest Remnants." Biological Conservation 91:223-229; Hardin, Garrett. 1968. "The Tragedy of the Commons." Science 162: 1243-1248; Hayes, Tyrone B., et al. 2002. "Hermaphroditic, Demasculinized Frogs after Exposure to the Herbicide Atrazine at Low Ecologically Relevant Doses." Proceedings of the National Academy of Science 99 (April 16): 5476-5480; Hunter, Mac L., Jr. 2001. Fundamentals of Conservation Biology, 2d ed. Malden, MA: Blackwell Science; Inter-governmental Panel on Climate Change (IPCC). 2001a. "Climate Change 2001: Impacts, Adaptation, Vulnerability: A Report of Working Group II of the IPCC, Approved at the Sixth Session of IPCC, Geneva, Switzerland, 13-16 February 2001,"; Intergovernmental Panel on Climate Change (IPCC). 2001b. "Climate Change 2001: The Scientific Basis: The Third Assessment Report of Working Group I of the IPCC, Approved at the Eighth Session of IPCC, Shanghai, China, 17-20 January 2001,"; Jackson, Jeremy B. C., et al. 2001. "Historical Overfishing and the Recent Collapse of Coastal Ecosystems." Science 293: 629-638; Laurance, William F., and Richard O. Bierregaard, Jr., eds. 1997. Tropical Forest Remnants. Chicago: University of Chicago Press; Laurance, William F., Heraldo L. Vasconcelos, and Thomas E. Lovejoy. 2000. "Forest Loss and Fragmentation in the Amazon: Implications for Wildlife Conservation." Oryx 34, no. 1: 39-45; Laurance, William F., and G. Bruce Williamson. 2001. "Positive Feedbacks among Forest Fragmentation, Drought, and Climate Change in the Amazon." Conservation Biology 15, no. 6: 1529-1535; Mack, Richard N., et al. 2000. "Biotic Invasions: Causes, Epidemiology, Global Conse quences and Control." Issues in Ecology 5: 1-20; Malcolm, Jay R., and Louis F. Pitelka. 2000. "Ecosystems and Global Climate Change: A Review of Potential Impacts on U.S. Terrestrial Ecosystems and Biodiversity." Prepared for the Pew Center on Global Climate Change.; Mooney, Harold A., and Richard J. Hobbs. 2000. Invasive Species in a Changing World. Washington, DC: Island Press; Nehring, Stefan. 2000. "Long-term Changes in Prosobranchia (Gastropoda) Abundances on the German North Sea Coast: The Role of the Antifouling Biocide Tributyltin." Journal of Sea Research 43: 151-165; Parmesan, Camille, et al.

1999. "Poleward Shifts in Geographical Ranges of Butterfly Species Associated with Regional Warming." Nature 399: 579-583; Pauly, Daniel, et al. 1998. "Fishing Down Marine Food Webs." Science 279: 860-863; Perakis, Steven S., and Lars O. Hedin. 2002. "Nitrogen Loss from Unpolluted South American Forests Mainly via Dissolved Organic Compounds." Nature 415: 416-419; Pimentel, David, et al.

2000. "Environmental and Economic Costs Associated with Nonindigenous Species in the United States." Bioscience 5, no. 1: 53-65; Pimm, Stuart L. 1989. "Theories of Predicting Success and Impact of Introduced Species." In Biological Invasions, a Global Perspective, edited by James A. Drake et al., pp. 351-367. New York: John Wiley and Sons; Quammen, David. 1998. "Planet of Weeds: Tallying the Losses of Earth's Animals and Plants." Harper's (October) pp. 57-69; Robinson, John G., and Elizabeth L. Bennett. 2000. Hunting for Sustainability in Tropical Forests. New York: Columbia University Press; Simberloff, Daniel S. 1986. "Are We on the Verge of a Mass Extinction in Tropical Rainforests?" In Dynamics of Extinction, edited by David K. Elliot, pp. 165-180. New York: Wiley-Interscience; Stirling, Ian, Nichoas J. Lunn, and John Iacozza. 1999. "Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change." Arctic 52, no. 3: 294-306; Vitousek, Peter M., et al. 1997. "Human Domination of Earth's Ecosystems." Science 277: 494-499; Wania, Frank, and Don Mackay. 1996. "Tracking the Distribution of Persistent Organic Pollutants." Environmental Science Technology 30: 390A-396A; Wilkinson, Clive. 1998. "The 1997-1998 Mass Bleaching Event around the World." In Status of Coral Reefs of the World: 1998, edited by Wilkinson, pp. 15-38. Global Coral Reef Monitoring Network.

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