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 per
Trang 1exists The most attractive for
indus-trial applications is H2production by
photosynthetic microbes These
mi-croorganisms, such as microscopic
algae, cyanobacteria, and
photosyn-thetic bacteria, use sunlight as an
en-ergy source and 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 fermentagenera-tion 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 all cars can use E10, fuel that is 10 percent
etha-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 greenhouse gas, 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” 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
This Volvo car runs on bioethanol, a biofuel manufactured from common household trash (AP/Wide World Photos)
Trang 2ture 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
run on compressed methane with gasoline as 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 CO2and 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 CO2, the process as a whole can be considered
“CO2neutral” in that the released CO2can 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 H2and O2 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 be used 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.
Trang 3Wright, 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 biologilo-cal 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 from one 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 Oror-ganisms 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 birds annually in Great Britain
It would seem logical to assume that invading
Trang 4cies 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 eliminate native 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 discovered a 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
The tunicate is an invasive species that grows in the habitat of
anemones and sea cucumbers (AP/Wide World Photos)
Trang 5eastern 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,
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 over less aggressive and less destructive
spe-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
Trang 6consider 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 than 1.0 percent in 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 tropostrato-sphere 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 of northern 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
Trang 7nant 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 Ground animals 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 shrubs resprout from the roots
af-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 sasa-vannas), 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 from recycled 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 phytoplankPlank-ton 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)
Trang 8Based 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 the Earth’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 standflow-ing-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’s surface 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 or deep), 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 discovered through 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 416 million 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
Trang 9phyllosilicates The word “biopyribole”
is a combination of “biotite” (a common
phyllosilicate), “pyroxene,” and
“amphi-bole.”
Pyroxenes are composed of chains of
silicate groups combined 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 groups combined with the same kinds of atoms as those
Augite is the most common pyroxene, a type of biopyribole (USGS)
Biopyribole Categories
Examples
Sheet silicates
Brittle mica group —
illite Serpentine Antigorite, chrysotile
asbestos
Chain silicates
Single silica tetrahedron
chains:
Monoclinic alkali
pyroxenes
Jadeite
Examples Monoclinic calcic
pyroxenes
Diopside, augite
Orthorhombic pyroxenes
Enstatite, hypersthene
Double silica tetrahedra chains:
Monoclinic alkali amphiboles
Glaucophane, riebeckite Monoclinic calcic
amphiboles
Tremolite, hornblende
Monoclinic magnesium-iron amphiboles
Cummingtonite
Orthorhobmic amphiboles
Anthophyllite
Trang 10found in pyriboles Most phyllosilicates are soft
miner-als with a density between 2 and 3 grams per cubic
cen-timeter Talc, a light-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 as micas, 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 his lectures, published in French in 1929 as La
Biosphere Vernadsky noted that the concept, although
not the term, had originated much earlier with the
French biologist Jean-Baptiste Lamarck (1744-1829)
Extent of the Biosphere
Although most people would think nothing of
travel-ing 50 kilometers to a nearby town, journeytravel-ing
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 indirectly from 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, cold mountaintop 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 upper latitudes 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