Encyclopedia of Global Resources part 15 pdf

exists. The most attractive for indus - trial applicationsis H 2 production by photosynthetic microbes. These mi- croorganisms, such as microscopic algae, cyanobacteria, and photosyn- thetic bacteria, use sunlight as an en- ergy sourceand water to generate hy- drogen. Butanol can be produced by the fermentation of sugars similar to the ethanol production. The most well- known pathway of butanol genera- tion is fermentation by bacterium Clostridium acetobutylicum. Substrates utilized for butanol production— starch, molasses, cheese whey, and lignocellulosic materials—are exactly the same as for ethanol fermenta- tion. The biological production by fermentation is not economically attractive because of low levels of product concentrations and high cost of product re- covery compared to the chemical process. Uses of Biofuels With increasing energy demands and oil prices, etha- nol has become a valuable option as an alternative transportation fuel. The Energy Policy Act of 2005 in- cluded a requirement to increase the production of ethanol from 15 to 28 billion liters by 2012. Beginning in 2008, a majority of fuel stations in the United States were selling gasoline with 10 percent ethanol in it. Nearly allcars can useE10, fuel thatis 10 percentetha- nol. Blending ethanol with gasoline oxygenates the fuel mixture, which burns more completely and pro- duces fewer harmful CO emissions. Another environ- mental benefit of ethanol is that it degrades in the soil, whereas petroleum-based fuels are more resis- tant to degradation and have many damaging effects when accidentally discharged into the environment. However, a liter of ethanol has significantly less en- ergy content than a liter of gasoline, so vehicles must be refueled more often. Ethanol is also more expen- sive than gasoline, although rising prices of gasoline could cancel that disadvantage. In addition, carcino- genic aldehydes, such as formaldehyde, are produced when ethanol is burned in internal combustion en- gines. Carbon dioxide, a major greenhousegas, forms as well. Moreover, the widely used fuel mix that is 85 percent ethanol and 15 percent gasoline (the E85 blend) requires specially equipped “flexible fuel” en - gines. In the United States, only a fraction of all cars are considered “flex fuel” vehicles. By comparison, however, most cars in Brazil have flex engines. Begin- ning in 1977, the Brazilian government made using ethanol as a fuel for cars mandatory. Brazil has the largest and most successful “ethanol for fuel” pro- gram in the world. As a result of this successful pro- gram, the country reached complete self-sufficiency in energy supply in 2006. Biodiesel performs similarly to diesel and can be used in unmodified diesel engines of trucks, tractors, and other vehicles, and it is better for the environ- ment. Burning biodiesel produces fewer emissions than petroleum-based diesel; it is essentially free of sulfur and aromatics and emits less CO. Additionally, biodiesel is less toxic to the soil. Biodiesel is often blended with petroleum diesel in different ratios of 2, 5, or 20 percent. The most common blend is B20, or 20 percent biodiesel to 80 percent diesel fuel. Biodiesel can be used as a pure fuel (100 percent or B100), but pure fuel is not suitable for winter because it thickens in cold temperatures. In addition, B100 is a solvent that degrades engines’ rubber hoses and gas- kets. Moreover, biodiesel energy content is less than in diesel. In general, biodiesel is not used as widely as ethanol. However, biodiesel users include the United States Postal Service; the U.S. Departments of De- fense, Energy,and Agriculture; national parks; school districts; transit authorities; and public-utilities, waste- management, and recycling companies across the United States. In January, 2009, Continental Airlines successfully demonstrated the use of a biodiesel mix - 110 • Biofuels Global Resources This Volvo car runs on bioethanol, a biofuel manufactured from common household trash. (AP/Wide World Photos) ture from plants and algae (50 percent to 50 percent) to fly its Boeing 737-800. In the 1985 Mel Gibson movie Mad Max Beyond Thunderdome, a futuristic city was run on methane that was generated by pig manure. In reality, methane can be a very good alternative fuel. It has a number of ad- vantages over other fuels produced by microorgan- isms. First, it is easy to make and can be generated lo- cally, which does not require distribution. Extensive natural gas infrastructure is already in place to be uti- lized. Second, the utilization of methane as a fuel is an attractive way to reduce wastes such as manure, wastewater, or municipal and industrial wastes. In lo- cal farms, manure is fed into digesters (bioreactors) where microorganisms metabolize it into methane. Methane can be used to fuel electrical generators to produce electricity. In China, millions of small farms have simple small underground digesters near the farm houses. There are several landfill gas facilities in the United States that generate electricity using meth- ane. San Francisco has extended its recycling pro- gram to include conversion of dog waste into meth- ane to produce electricity and to heat homes. With a dog population of 120,000 this initiative promises to generate a significant amount of fuel with a huge re- duction of waste at the same time. Methane was used as a fuel for vehicles for a number of years. Several Volvo car models with bi-fuel engines were made to runon compressed methane with gasolineas a backup. Biogas can also be compressed, like methane, and used to power motor vehicles. In many countries, millions of small farms main- tain a simple digester for biogas production to gener- ate energy. Currently, there are more than five million household digesters in China, used by people mainly for cooking and lighting, and there are more than one million biogas plants of various capacities in India. Utilization of methane and biogas as an energy source in place of fossil fuels is providing significant environmental and economic benefits. Biofuels are essentially nonpolluting, although their utilization re- sults in production of CO 2 and contributes to global warming, though with less impact on Earth’s climate than methane itself as a greenhouse gas. Even though the use of methane and biogas as energy sources re- leases CO 2 , the process as a whole can be considered “CO 2 neutral” in that the released CO 2 can be assimi - lated by their producers, archaea and bacteria. Some examples of biomass use as an alternative energy source include burning wood or agricultural residue to heat homes. This is an inefficient use of energy—typically only 5-15 percent of the biomass en- ergy is actually utilized. Using biomass that way pro- duces harmful indoor air pollutants such as carbon monoxide. Yet biomass is an almost “free” resource costing only labor to collect. Biomass supplies more than 15 percent of the world’s energy consumption. Biomass is the top source of energy in developing countries; in some countries it provides more than 90 percent of the energy used. Hydrogen powered U.S. rockets for many years. To- day, a growing number of automobile manufacturers around the world are making prototype hydrogen- powered vehicles. Only water is emitted from the tail- pipe—no greenhouse gases. The car is moved by a motor that runs on electricity generated in the fuel cell via a chemical reaction between H 2 and O 2 .Hy- drogen vehicles offer quiet operation, rapid accelera- tion, and low maintenance costs. During peak time, when electricity is expensive, fuel-cell hydrogen cars could provide power for homes and offices. Hydro- gen for these applications is obtained mainly from natural gas (methane and propane) via steam reform- ing. Biohydrogen is used in experimental applica- tions only. Many problems need to be overcome be- fore biohydrogen can be easily available. One of the reasons for the delayed acceptance of biohydrogen is the difficulty of its production on a cost-effective basis. For biohydrogen power to become a reality, tre- mendous research and investment efforts are neces- sary. Butanol can be used as transportation fuel. It con- tains almost as much energy as gasoline and more en- ergy than ethanol for a particular volume. Unlike 85 percent ethanol, a butanol/gasoline mix (E85 blend) can beused in cars designed for gasoline without mak- ing any changes to the engine. Sergei A. Markov Further Reading Chisti, Yusuf. “Biodiesel from Microalgae.” Biotechnol- ogy Advances 25, no. 3 (2007): 294-306. Glazer, Alexander N., and Hiroshi Nikaido. Microbial Biotechnology: Fundamentals of Applied Microbiology. New York: W. H. Freeman, 2007. Service, Robert F. “The Hydrogen Backlash.” Science 305, no. 5686 (August 13, 2004): 958-961. Wald, Matthew L. “Is Ethanol for the Long Haul?” Sci - entific American 296, no. 1 (January, 2007): 42-49. Global Resources Biofuels • 111 Wright, Richard T. Environmental Science: Towards a Sustainable Future. 9th ed. Englewood Cliffs, N.J.: Prentice Hall, 2004. Web Site AE Biofuels http://www.alternative-energy-news.info/ technology/biofuels/ See also: Brazil; Energy economics; Ethanol; Meth- ane; Sugars; Sustainable development. Biogeochemical cycles. See Carbon cycle; Geochemical cycles; Hydrology and the hydrologic cycle; Nitrogen cycle; Phosphorus cycle; Sulfur cycle Biogeographic realms. See Ecozones and biogeographic realms Biological invasions Categories: Environment, conservation, and resource management; pollution and waste disposal A biological invasion is an enormous increase in the numbers of a type of organism entering an ecosystem that the organism previously was not inhabiting. The “invading” organism may be an infectious virus, a bacterium, a plant, or an animal. Background Species introduced to an area from somewhere out- side that area are referred to as alien or exotic species or as invaders. Because the exotic species is not native to the new area, it is often unsuccessful in establishing a viable population and disappears. The fossil record, as well as historical documentation, indicates that this is the fate of many exotic species as they move from their native habitats to invade new environments. Oc - casionally, however, an invading species finds the new environment to its liking; in this case the invader may become so successful in exploiting its new habitat that it can completely alter the ecological balance of an ecosystem, destroying biodiversity and altering the lo- cal biological hierarchy. Because of this ability to alter ecosystems, exotic invaders are considered major agents in driving native species to extinction and are thought to be responsible for an estimated 40 percent of all known extinctions of land animals beginning in the year 1600. Biological invasions by notorious species consti- tute a significant component of Earth’s history. In general, large-scale climatic changes and geological crises are at the origin of massive exchanges of flora and fauna. On a geologic timescale, invasions of spe- cies fromone continent to another are true evolution- ary processes, just as speciation and extinction are. On a smaller scale, physical barriers such as oceans, mountains, and deserts can be overcome by many or- ganisms as their populations expand. Organisms can be carried by water in rivers or ocean currents, trans- ported by wind, or carried by other species as they mi- grate seasonally or to escape environmental pres- sures. However, the geological and historical records of the Earth also show that specific biological inva- sions by exotic species have altered the course of world history. The extinction of genetically distinct populations is the least reversible of all global changes, and evidence suggests that biological invasions con- tribute substantially to an increase in the rate of ex- tinction within ecosystems. Humans have transplanted species throughout his- tory, to the point where most people are not aware of the distinction between native and exotic species liv- ing in their region. Recent increases in interconti- nental invasion rates by exotic species, brought about primarily by human activity, create important ecologi- cal problems for the recipient lands. Among animals, the most notorious recent invaders of North America have been the house mouse and the Norway rat; others include the wild boar, donkey, horse, nutria, Pierid butterfly, house sparrow, starling, Africanized (“killer”) bee, tiger mosquito, and red fox. One of the most destructive invaders is the house cat. More than seventy million domestic and feral cats live in the United States, and they are efficient at hunting small mammals and birds. Domestic cats are credited with killing twenty million birdsannually in Great Britain. It would seem logical to assume that invading spe - 112 • Biological invasions Global Resources cies might add to the biodiversity of a region, but many invaders have the opposite effect. The new spe- cies are often opportunistic and successful predators that eliminatenative species not adapted to their pres- ence. For example, the brown tree snake was acciden- tally introduced to Guam during World War II as a stowaway on military cargo ships, and the snakes have eliminated most of the island’s birds. The snakes are credited with the extinction of one-third of the is- land’s native bird species, and the surviving bird pop- ulation is so decimated that birds are rarely seen or heard. The invasion of the brown tree snake has unal- terably reduced the biological diversity of Guam. Ecosystem Alteration The invasion of an ecosystem by an exotic species can effectively alter ecosystem processes. An invading species does not simply consume or compete with na- tive species but can actually change the rules of exis- tence within the ecosystem by altering processes such as primary productivity, decomposition, hydrology, geomorphology, nutrient cycling, and natural distur- bance regimes. Invading exotic species may also drive out native species by competing with them for re - sources. One of the exotic invaders of the North American continent is the zebra mussel, which came to the United States in 1986 in the ballast water of oceangoing vessels; it was carried from the Elbe or Rhine River in Europe and released into the water of the St. Clair River near Detroit, Michigan. The mussel larvae found biological conditions in the Great Lakes ideal. The mussel now exists in all the Great Lakes, and after the catastrophic flood of 1993 the mussels were sighted in the Mississippi River Basin. Mussel density in certain locations of the Great Lakes is known to be astonishing—greater than 94,000 indi- viduals per square meter. In 1990, the Detroit Edison power plant discovereda water intake pipe blocked by a mussel population density of 700,000 mussels per square meter. When they reach high population den- sities, the mussels are able to filter virtually all the larger plankton from the water. The planktonic food chain of the Great Lakes, which supports Great Lakes fisheries, may decline so much that higher trophic species will be deprived of their vital plankton food sources. The mussels also cause a demise of native bi- valves through competition for food and because they attach themselves to the shells of other bivalves. Forests The invasion of native forests by non-native insects and microorganisms has been devastating on many continents. The white pine blister rust and the balsam woolly adelgid have invaded both commercial and preserved forestlands in North America. Both exotics were brought to North America in the late 1800’s on nursery stock from Europe. The balsam woolly adelgid attacks fir trees and causes death within two to seven years by causing chemical damage and by feed- ing on the tree’s vascular tissue. The adelgid has killed nearly every adult cone-bearing fir tree in the south- ern Appalachian Mountains. The white pine blister rust attacks five-needle pines; in the western United States fewer than 10 pine trees in 100,000 are resis- tant, and since white pine seeds are an essential food source for bears and other animals, the loss of the trees has had severe consequences across the forest food chain. Beginning in the 1800’s the deciduous forests of eastern North America were attacked numerous times by waves of invading exotic species and diseases. One of the most notable invaders is the gypsy moth, which consumes a variety of tree species. Other invaders of Global Resources Biological invasions • 113 The tunicate is an invasive species that grows in the habitat of anemones and sea cucumbers. (AP/Wide World Photos) eastern forests have virtually eliminated the once dominant American chestnut and the American elm. Other tree species that continue to decline because of new invaders include the American beech, mountain ash, white birch, butternut, sugar maple, flowering dogwood, and eastern hemlock. It is widely accepted that the invasion of exotic species is the single greatest threat to the diversity of deciduous forests in North America. Effects on Humans, and Humans as Invaders Some introduced exotic species are beneficial to hu- manity. It would be impossible to support the present world human population entirely on species native to their regions. However, many invading species de- grade human health and wealth, and others affect the structure of ecosystems or the ability to maintain na- tive biodiversity. Many invading species can act as vec- tors of disease: Examples include bubonic plague, vectored by rats; a host of diseases transmitted be- tween human populations during first contacts, in- cluding smallpox, polio, influenza, and venereal in- fections; and malaria, dengue fever, Ross River fever, and eastern equine encephalitis, carried by mosqui- toes. Mosquitoes alone are thought to account for half of all human deaths throughout history. Humans, the ultimate biological invaders, have been responsible for the extinction of many species and will continue to be in the future. Like other ani- mal invaders, humans tend to have a broad diet. Hu- mans are also able to adapt culturally to diverse habi- tats, an ability that complements an ability to breed all year round. These attributes give humans a distinct advantage overless aggressive and less destructivespe- cies. Randall L. Milstein Further Reading Burdick, Alan. Out of Eden: An Odyssey of Ecological Inva- sion. New York: Farrar, Straus and Giroux, 2005. Cartwright, Frederick F., and Michael Biddiss. Disease and History. 2d ed. Stroud, England: Sutton, 2000. Crosby, Alfred W. Ecological Imperialism: The Biological Expansion of Europe, 900-1900. 2d ed. New York: Cambridge University Press, 2004. Elton, Charles S. The Ecology of Invasions by Animals and Plants. London: Methuen, 1958. Reprint. Chicago: University of Chicago Press, 2000. Hengeveld, Rob. Dynamics of Biological Invasions. New York: Chapman and Hall, 1989. Lockwood, Julie L., Martha F. Hoopes, and Michael P. Marchetti. Invasion Ecology. Malden, Mass.: Black- well, 2007. Mooney, Harold A., and James A. Drake, eds. Ecology of Biological Invasions of North America and Hawaii.New York: Springer, 1986. Mooney, Harold A., and Richard J. Hobbs, eds. Inva- sive Species in a Changing World. Washington, D.C.: Island Press, 2000. Nentwig, Wolfgang, ed. Biological Invasions. New York: Springer, 2007. Pimentel, David, ed. Biological Invasions: Economic and Environmental Costs of Alien Plant, Animal, and Mi- crobe Species. Boca Raton, Fla.: CRC Press, 2002. Web Site University of Tennessee, Department of Ecology and Environmental Biology Institute for Biological Invasions http://invasions.bio.utk.edu See also: Genetic diversity; Pesticides and pest con- trol; Species loss. Biomes Category: Ecological resources Biomes (terrestrial and aquatic ecosystems) are distrib- uted throughout the Earth’s surface. Terrestrial biomes occupy the landmass from North Pole to South Pole. Aquatic biomes occupy the bodies of water on Earth. Background Biomes are natural habitats for bacteria, protists, fungi, plants, and animals. Biomes maintain the natu- ral life cycle of these organisms and preserve the products of geological processes on Earth. A biome is a source of shelter, rocks and minerals, and food and fiber for human needs. Technical Definition A terrestrial biome is a large ecosystem characterized by a particular type of climate and soils with defined groups of highly adapted living organisms. Biome for- mation is influenced by warm temperature and heavy precipitation in the tropics and extreme cold and low precipitation near the poles. Most ecologists do not 114 • Biomes Global Resources consider aquatic ecosystems as biomes and refer to them as “aquatic biomes,” which are classified based on the concentration of dissolved salts: less than 0.1 percent in freshwater biomes, 0.1 to 1.0 percent in es- tuaries, and more than1.0 percentin marine biomes. Climate and Biomes Climate shapes terrestrial biomes. Climate is predom- inantly driven by the solar energy and atmospheric circulation. Air circulation is initiated at the equator, because the equator receives the greatest solar energy with the warmest air near the ground. Because of dif- ferent air densities, warm air in the troposphere rises into the stratosphere and cools. Cool air in the strato- sphere descends into troposphere and warms. This rise and fall pattern of circulating air starts at 0° (equator) to 30° latitude, then continues at 30° to 60° latitude, and ends at 60° to 90° latitude (poles). There are six major atmospheric circulations: Three move from the equator to the North Pole; the other three move from the equator to the South Pole. At 0° latitude, the ascending warm, humid air from the troposphere cools and condenses as it reaches the stratosphere, releasing heavy rain to or near the equa- tor. That the dominant biomes formed at the equator are the tropical rain forests is no accident. After re- leasing rain, the cool, dry air moves poleward and de- scends at 30° latitude. The descending cool, dry air becomes warm as it reaches the troposphere and then absorbs all the available moisture. Not surprisingly, the dominant biomes at 30° latitude are the deserts, where the warm, humid air splits. One air mass moves equatorward to recirculate at 0° latitude. The other moves poleward and rises at 60° latitude, releasing rain or snow while at the stratosphere. As a result, the dom- inant biomes at 60° latitude are the temperate forests and temperate grasslands. The cool, dry air at the stratosphere divides again 60° latitude. One air mass moves toward 30° latitude to descend and recirculate in the desert. The other moves poleward, then de- scends and releases the remaining moisture near the poles, where the arctic tundra biomes are formed. Terrestrial Biomes The are nine major terrestrial biomes. Arctic Tundra. Arctic tundra is located in the Northern Hemisphere near the North Pole and cov- ers 20 percent of Earth’s landmass. It has extremely long, freezing, and harsh winters, with very short (six- to eight-week) summers. It is considered “cold desert,” because it receives 20 centimeters of precipitation per year. Melting snow creates bogs in summer, but there are frozen layers of subsoil (permafrost) at least a meter deep that exist throughout the year. Soil is nutrient-poor. Only the low-growing grasses and dwarf woody shrubs adapted to extreme cold and a short growing season are found. No trees survive. Their roots cannot penetrate the permafrost. Few ani- mal species live in tundra. In winters, ptarmigans, musk oxen, snowy owls, lynxes, arctic foxes, and snow- shoe hares are found. Polar bears are common in the coastal regions. In summers, few migrating animals from taiga move to tundra. No reptiles are found, but mosquitoes survive. Taiga. Taiga, also called boreal coniferous forest, exists south of tundra and covers 11 percent of the Earth’s land surface. It is found in the northern parts of North America and Eurasia and along the Pacific coast ofnorthern North America to Northern Califor- nia. It has patchy and shallower permafrost than tun- dra, and has acidic, nutrient-poor soil. It has short summers and long, cold winters and receives 50 centi- meters precipitation per year. Evergreen conifers are adapted to these conditions, with low-lying mosses and lichens beneath the forest canopy. Seeds of coni- fers attract birds. Bears, deer, moose, beavers, musk- rats, wolves, mountain lions, and wolverines inhabit the taiga. Temperate Rain Forest. Temperate rain forest, a coniferous forest, stretches along the west coast of Canada and the United States, the southeast of Aus- tralia, and the south of South America. It has dense fog, mild winters, cool summers, and high annual pre- cipitation of 250 centimeters. With abundant rain and nutrient-rich soil, the temperate rain forests have re- tained some of the tallest conifers (such as coastal red- woods) and oldest trees, some as old as eight hundred years. Moisture-loving plants (mosses and ferns) grow on the tree trunks of evergreen conifers. Temperate rain forest is a habitat for squirrels, lynxes, and several species of amphibians, reptiles, and birds (such as the spotted owl). Temperate Deciduous Forest. Temperate decid- uous forest is located south of the taiga in eastern North America, eastern Asia, and much of Europe. Temperate deciduous forests have a moderate cli- mate, with occasional hot summers and cold winters and high annual precipitation of 75 to 150 centime - ters. They have long growing seasons ranging from 140 to 300 days. The soil is rich in minerals. The domi - Global Resources Biomes • 115 nant trees are deciduous (oak, beech, sycamore, and maple), which shed their broad leaves in the fall and grow them in the spring. Under the forest’s canopy, understory trees and shrubs are found. Layers of growth in the forest are home for several insects and birds. Groundanimals include rabbits,squirrels, wood- chucks, chipmunks, turkeys, beavers, and muskrats. Temperate Grasslands. Temperate grasslands in- clude the South American pampas, the Russian steppes, and the North American prairies. Tall-grass prairies are found between Illinois and Indiana, whereas short-grass prairies extend from Texas to Montana and North Dakota. They have hot and dry summers and bitterly cold winters, with annual pre- cipitation of 25 to 75 centimeters. Grasses in these biomes produce a deep, dark, mineral-rich soil. Her- bivore mammals (bison, pronghorn antelope, mice, prairie dogs, and rabbits) dominate the temperate grasslands. Hawks, snakes, badgers, coyotes, and foxes are the predators in this biome. Shrubland. Shrubland, or chaparral, is composed of thickets of small-leaf evergreen shrubs (shorter than trees and without main trunks). Shrublands, with frequent fires in dry summers and winters of 25 to 75 centimeters of rain annually, are found along the cape of South Africa, the western coast of North America, the southwestern and southern shores of Australia, around the Mediterranean Sea, and in cen- tral Chile. The shrubland in California is called chap- arral, because it lacks understory. Shrubs are fire- adapted and highly flammable. The seeds of many species require the scarring action of fire to induce germination. Other shrubsresprout fromthe rootsaf- ter fire. Mule deer, rodents, scrub jays, and lizards in- habit the shrublands. Deserts. Deserts exist near or at 30° north and south latitudes and cover approximately 30 percent of the Earth’s land surface. The dry air that descends in this region absorbs most of the available moisture, then moves away to the equator and to 60° latitude. Deserts receive less than 25 centimeters of rain annu- ally. The Sahara Desert of Africa and the Arabian Peninsula and the deserts of North America (Mojave, Chihuahuan, and Sonoran) have little or no vegeta- tion. Organisms with specialized water-conserving adaptations survive, including cactus, agave, Joshua trees, and sagebrush plants. Hawks prey on lizards, snakes, roadrunners, and kangaroo rats. Tropical Grasslands. Tropical grasslands, or sa - vannas (such as African savannas), characterized by widespread growth of grasses with few interspersed trees, are found in areas with seasonal low rainfall and prolonged dry periods. Other savannas occur in South America and northern Australia. Savanna has an annual precipitation of 25 to 75 centimeters. Sa- vanna soil is nutrient-poor.Acacia trees survive the se- vere dry season. Hoofed herbivore mammals (giraffes, elephants, zebras, and rhinoceroses) feed on tree veg- etation and on grasses. Carnivores such as hyenas, lions, cheetahs, and leopards prey on herbivores. Tropical Rain Forests. Tropical rain forests are located in South America, Africa, Southeast Asia, and the Indo-Malayan region on or near the equator. Wet and dry seasons are warm year-round. Annual rainfall is 200 to 450 centimeters. Tropical rain forest soil is typically nutrient-poor, but plentiful rain supports the growth of diverse groups of woody and herbaceous plants. Some of the rains come fromrecycled water re- leased by forest trees by transpiration. Of all the biomes, tropical rain forest is the richest, based on species diversity, productivity, and abundance of all organisms. Tropical rain forest has three levels: the canopy (the highest layer of the forest), the under- story (middle layers of small trees and shrubs), and forest floor (ground layers of herbaceous plants). Epiphyte plants (such as bromeliads, orchids, ferns, and Spanish moss) gain access to sunlight by growing on trunks and branches of tall trees. Lemurs, sloths, and monkeys are tree-dwelling primates that feed on fruits. The largest carnivores in the tropical rain forest are the jaguars in South America and the leopards in Africa and Asia. Aquatic Biomes All aquatic biomes share three ecological groups of organisms: the plankton, nekton, and benthos. Plank- ton are classified into microscopic phytoplankton and large zooplankton. Phytoplankton are producers and include photosynthetic cyanobacteria and free- floating algae, which provide oxygen and food for heterotrophic organisms. Zooplankton are consum- ers, heterotrophic, nonphotosynthetic organisms that include protozoa, small crustaceans, and larvae of aquatic animals. Nekton are larger swimming ani- mals such as turtles, fishes, and whales. Benthos are bottom-dwelling animals that attach themselves to a substratum (sponges, oysters, and barnacles), bur- row themselves into soil (clams, worms, and echi - noderms) or simply swim or walk on the bottom (cray - fish, crabs, lobsters, insect larvae, and brittle stars). 116 • Biomes Global Resources Based on salt contents, the three major aquatic eco - systems are the freshwater, estuary,and marine ecosys- tems. Freshwater ecosystems, which contain less than 0.1 percent dissolved salts and occupy about 2 percent of theEarth’s surface,include flowing waters (streams and rivers), standing waters (ponds and lakes), and freshwater wetlands (marshes and swamps). While all freshwater habitats provide homes for animal species, greater vegetations are found in marshes (grasslike plants) and in swamps (trees and shrubs) than in flow- ing- and standing-water ecosystems. Estuaries occur where fresh water and salt water meet, with salt con- centrations of 0.1 to 1.0 percent. Temperate estuaries called salt marshes are dominated by salt-tolerant grasses. Tropical estuaries are called mangrove for- ests. Marine ecosystems, which contain more than 1.0 percent dissolved salts, dominate, occupying about 70 percent of the Earth’ssurface. Marine biomes have three zones: the intertidal, pelagic, and benthic zones. The intertidal zone is the shoreline area between low and high tide. The pelagic zone is the ocean water (shallow ordeep), where plankton and swimming ma- rine organisms are found. The benthic zone is the ocean floor, where marine animals burrow. Coral reefs, kelp forests, and seagrass beds are part of the benthic zone. History The existence of aquatic and terrestrial ecosystems was discoveredthrough fossil records.Aquatic biomes emerged before the terrestrial biomes. Approximately 542 million years ago, during the Cambrian period, organisms in marine biomes became diversified and included bacteria, cyanobacteria, algae, fungi, ma- rine invertebrates, and first chordates. The first ter- restrial biome existed when the first forest and gym- nosperm appeared about 416million years ago, during the Denovian period. About 359 million years ago, during the Carboniferous period, the formation of much more diversified forest occurred, which con- sisted of ferns, clubmosses, horsetails, and gymno- sperms and which housed many insects, amphibians, and first reptiles. Flowering plants (angiosperms) later evolved and became the dominant organisms of most major biomes. Domingo M. Jariel Further Reading Kirchner, Renee. Biomes. Detroit: KidHaven Press/ Thomson Gale, 2006. Roth, Richard A. Freshwater Aquatic Biomes. Westport, Conn.: Greenwood Press, 2009. Solomon, Eldra Pearl, Linda R. Berg, and Diana W. Martin. “Ecology and the Geography of Life.” In Bi- ology.8th ed. Monterey, Calif.: Brooks/Cole,2008. Woodward, Susan L. Marine Biomes. Westport, Conn.: Greenwood Press, 2008. Web Site University of California Museum of Paleontology http://www.ucmp.berkeley.edu/exhibits/biomes/ index.php See also: Biodiversity; Biosphere;Biosphere reserves. Biopyriboles Category: Mineral and other nonliving resources Biopyriboles are minerals composed of linked silicate groups. Some hard biopyriboles are used as gemstones. Fibrous biopyriboles are used to manufacture asbestos. Micas are used in electrical components and as fillers, absorbents, and lubricants. Clays are used in bricks, pottery, and fillers. Definition Biopyriboles are a large and varied group of minerals in which silicate groups (one silicon atom bonded to four oxygen atoms) are linked together in one- dimensional chains (either single chains or two chains linked together) or two-dimensional sheets. Those with chains are usually hard, while those with sheets are usually soft. Hard biopyriboles are usually found as separate minerals within igneous and meta- morphic rocks. Soft biopyriboles are usually found as flakes of mica within rocks or as particles of clay in soils and freshwater sediments. Overview There are three broad categories of biopyriboles, depending on whether the silicate groups are linked together into single chains, double chains, or sheets. Single-chain biopyriboles are known as pyroxenes. Double-chain biopyriboles are known as amphiboles. Together these two subgroups are known as pyriboles or inosilicates. Sheet biopyriboles are known as Global Resources Biopyriboles • 117 phyllosilicates. The word “biopyribole” is a combination of “biotite” (a common phyllosilicate), “pyroxene,” and “amphi- bole.” Pyroxenes are composed ofchains of silicate groupscombined with a wide va- riety of other atoms, including sodium, magnesium, calcium, iron, and alumi- num. They are generally fairly hard min- erals with a density between three and four grams per cubic centimeter. Pyrox- enes are usually dark green or black, but other colors also exist. The most common pyroxene is augite, a green or black mineral sometimes used as a gem- stone. Spodumene is a white, light gray, or light yellow pyroxene that contains lithium. It is the most important source of that element. Jadeite, a type of jade, is a green py- roxene used as a gemstone. Amphiboles are composed of two linked chains of silicate groups combined with the same variety of at- oms as those found in pyroxenes. They also contain hydroxyl groups (one oxygen atom bonded to one hy- drogen atom), which cause them to release water when heated. At high temperatures the double chains break down into single chains to form pyroxenes. Am- phiboles are fairly hard minerals with a density be- tween 2.9 and 3.6 grams per cubic centimeter. The most common amphibole is hornblende, a dark green or black mineral. Nephrite, a green amphibole, is a form of jade. Phyllosilicates are composed of sheets of silicate groupscombined with thesame kindsof atoms asthose 118 • Biopyriboles Global Resources Augite is the most common pyroxene, a type of biopyribole. (USGS) Biopyribole Categories Examples Sheet silicates Brittle mica group — Chlorite — Clays Kaolinite, smectite, illite Serpentine Antigorite, chrysotile asbestos Talc Talc, pyrophyllite Mica Biotite, moscovite Chain silicates Single silica tetrahedron chains: Monoclinic alkali pyroxenes Jadeite Examples Monoclinic calcic pyroxenes Diopside, augite Orthorhombic pyroxenes Enstatite, hypersthene Pyroxenoids Wollastonite Double silica tetrahedra chains: Monoclinic alkali amphiboles Glaucophane, riebeckite Monoclinic calcic amphiboles Tremolite, hornblende Monoclinic magnesium- iron amphiboles Cummingtonite Orthorhobmic amphiboles Anthophyllite found inpyriboles. Most phyllosilicates are softminer - als witha density between 2 and 3 grams per cubic cen- timeter. Talc,alight-colored, very soft phyllosilicate, is used in paint, ceramics, and talcum powder. Serpen- tine, a green, fibrous mineral, is used to make asbestos. Many phyllosilicates exist as clays, used in ceramics and fillers, or asmicas, used in electrical components. Rose Secrest See also: Asbestos; Clays;Gems; Mica; Silicates; Talc. Biosphere Category: Ecological resources The biosphere is the relatively thin layer around the Earth’s surface where life is naturally possible. The concept is important in ecology for the calculation of energy and mineral resource budgets, in space explora- tion for the establishment and maintenance of livable environments for space travelers, and perhaps for un- derstanding the possibilities for life on other planets. Background The first use of the term “biosphere” dates to 1875, when geologist Eduard Suess described layers of the Earth in his book on the origin of the Alps. The Rus- sian geologist Vladimir Vernadsky popularized the term in hislectures, published in French in 1929 as La Biosphere. Vernadsky noted that the concept, although not the term, had originated much earlier with the Frenchbiologist Jean-Baptiste Lamarck(1744-1829). Extent of the Biosphere Although most people would think nothing of travel- ing 50 kilometers to a nearby town, journeying up- ward far less than this distance would mean certain death without a special support system. As altitude in- creases, decreases in pressure, vital gases, and temper- ature prevent active metabolism. However, dormant bacterial and fungal spores can apparently drift up- ward indefinitely in this “parabiosphere.” Most jet plane passengers are aware that artificial cabin pres- sure is required to sustain them in the thinning atmo- sphere when they are only a few kilometers high. Chlorophyll plants cannot live above about 6,200 me - ters because all water freezes at that altitude and the carbon dioxide available for photosynthesis is at less than half that available at sea level. The few spiders and springtails that live on top of Mount Everest sur- vive on plant and animal debris blown up there by wind currents. Life also extends downward into the deepest ocean trenches, although the density of organisms is drasti- cally less in the dark zones beneath the thin top layer, where sunlight feeds algae and the resultant food chains. Most deep-ocean organisms must feed on the rain of organic matter that sinks from the surface or feed in the detritus food chain. Many organisms live on the surface of the ocean bottom, and sampling studies have shown that life extends deep into these bottom muds. Not all organisms here derive their en- ergy indirectlyfrom plant photosynthesis;some thrive on food chains originating with sulfur bacteria. Or- ganisms that have evolved to live under the tremen- dous water pressure of the lower oceans burst open if pulled to the surface; conversely, humans would be crushed at these depths, so exploration requires heavy protective equipment. Like deep-ocean fish brought to the surface, humans decompress when ex- posed at high altitudes. Therefore, much of the bio- sphere is beyond humans’ day-to-day reach. Biomes The terrestrial part of the biosphere can be subdi- vided into such categories as hot and wet tropical rain forests, frozen arctic tundra, coldmountaintop mead- ows, and prairie grasslands. These natural communi- ties with similar plants and animals are called “bi- omes.” For example, conifer forests stretch around the upperlatitudes of Canada, Europe, and Russia. Al- though the species of conifer trees, large grazers, and predators differ, the ecology is very similar. The same is true for the grassland biome that occurs in the U.S. plains states, Russia, Argentina, and South Africa, and the temperate deciduous forests of the eastern United States, Europe, and China. Other biomes in- clude taiga, savanna, thornbush, chaparral, and vari- ous tropical rain forest types. The first breakdown of biotic communities was made by C. Hart Merriam, working in 1890 in Califor- nia and Arizona; his “vegetative life zones” were based on temperature and ignored rainfall. Victor E. Shel- ford added detailed descriptions of animal associa- tions but did not try to correlate communities with cli- mate. While Shelford’s followers consider biomes to be distinct entities, other ecologists view them as hu - man concepts that hide the fact that communities Global Resources Biosphere • 119 . a form of jade. Phyllosilicates are composed of sheets of silicate groupscombined with thesame kindsof atoms asthose 118 • Biopyriboles Global Resources Augite is the most common pyroxene, a type of. Continental Airlines successfully demonstrated the use of a biodiesel mix - 110 • Biofuels Global Resources This Volvo car runs on bioethanol, a biofuel manufactured from common household trash. (AP/Wide. invading exotic species and diseases. One of the most notable invaders is the gypsy moth, which consumes a variety of tree species. Other invaders of Global Resources Biological invasions • 113 The