CHAPTER 36 ECOSYSTEMS AND CONSERVATION BIOLOGY
Concept 36.1 FEEDING RELATIONSHIPS DETERMINE THE PATH OF ENERGY AND CHEMICALS IN ECOSYSTEMS
ENERGY FLOW AND CHEMICAL CYCLING • Producers: (plants) convert light energy to chemical energy of organic compounds (photosynthesis) • Consumers: obtain chemical energy by feeding on producers or other consumers • Decomposers: break down wastes and dead organisms (detritus)
FOOD CHAINS • Trophic levels: a feeding level • Food chain: pathway of food transfer from one trophic level to another
TYPES OF CONSUMERS CLASSIED BY WHAT THEY EAT • Herbivore: eats only producers • Carnivore: eats only other consumers • Omnivore: eats both producers and consumers
Classified by position in food chain Primary consumer: 1st level - eat producers Secondary consumer: 2nd level - eat primary consumers Tertiary consumer: 3rd level - eat secondary consumers Quaternary consumer: 4th level - eat tertiary consumers TYPES OF CONSUMERS
Concept 36.2 ENERGY FLOWS THROUGH ECOSYSTEMS
BIOMASS • Biomass: organic material made by producers • Primary productivity: the rate at which producers in an ecosystem build biomass • Level of primary productivity in an ecosystem determines how much energy is available to all the higher trophic levels in an ecosystem
Energy pyramid: shows energy loss that occurs from one trophic level to another Only 10% of energy available at one trophic level is converted to biomass at the next higher trophic level—rest is lost from the ecosystem as heat ECOLOGICAL PYRAMIDS
ECOLOGICAL PYRAMIDS • Biomass pyramid: depicts actual biomass (dry mass of all organisms) in each trophic level in an ecosystem • Pyramid of numbers: depicts the number of individual organisms in each trophic level in an ecosystem
Concept 36.3 CHEMICALS CYCLE IN ECOSYSTEMS
PATTERN OF CHEMICAL CYCLING • Producers incorporate chemicals from the nonliving environment into organic compounds. • Consumers feed on producers, incorporating some of the chemicals into their own bodies • Consumers release some chemicals back to the environment in waste products. • As organisms die, decomposers break them down, further supplying soil, water, and air with chemicals in inorganic form. • Producers gain a renewed supply of raw materials for building organic matter, and the cycle continues
Carbon is found carbon dioxide gas (CO2) in the atmosphere Carbon is also found in water in dissolved form as HCO3 Producers use these carbon and oxygen atoms form organic compounds during photosynthesis This organic carbon cycles to consumers as food. CARBON & OXYGEN CYCLE
CARBON & OXYGEN CYCLE • In cellular respiration, organisms break down organic compounds and release carbon dioxide gas as a waste product • Carbon dioxide also is released to the atmosphere as decomposers break down detritus. • Burning fossil fuels, burning wood (from natural forest fires and from human activities), & geologic events such as volcanic eruptions add more carbon dioxide gas to the atmosphere.
Nitrogen fixation: bacteria convert the nitrogen gas to ammonia (NH3) Nitrogen-fixing bacteria live in soil and on roots of plants such as peas, beans, alfalfa, and clover Nitrification: bacteria in soil convert ammonium to nitrates Producers absorb the ammonium and nitrates from the soil and use them to build amino acids, proteins, and nucleic acids THE NITROGEN CYCLE
The sun evaporates water from land and water surfaces, adding gaseous water vapor to the atmosphere As it cools, water vapor condenses and falls as precipitation Plants absorb this water from soil, and consumers obtain water by eating and drinking. THE WATER CYCLE
THE WATER CYCLE • A large amount of water exits plants during transpiration, evaporation from the plant's leaves • Water not held by plants or bound to soil particles either runs off into rivers and streams or restores groundwater • Eventually, this water may reenter the atmosphere through evaporation, and the cycle continues.
Concept 36.4 HUMAN ACTIVITIES CAN ALTER ECOSYSTEMS
Burning of wood and fossil fuels is major source of carbon dioxide in the atmosphere Industrialization has led to steadily rising atmospheric carbon dioxide levels Carbon Cycle Impacts
How are increased CO2 levels in the atmosphere significant? • Greenhouse effect: CO2 is one of a few gases in the atmosphere that allow sunlight to pass through to Earth, but traps some heat as it is reflected from Earth's surface • These gases act somewhat like glass windows in greenhouses that allow light in, but prevent heat from escaping • Results in Earth's surface temperature being higher than it would be if all heat escaped into space • As levels of CO2 and other "greenhouse gases" rise, more heat is trapped raising Earth's average temperature. Such an overall rise in Earth's average temperature is called global warming.
DEFORESTATION • Deforestation: clearing of forests for agriculture, lumber, and other uses • Affects carbon cycle by eliminating plants that absorb CO2 during photosynthesis • After being cut down, the trees may be burned, releasing more carbon dioxide • Burning after deforestation in the tropics accounts for about 20 percent of the carbon dioxide added to the atmosphere by human activities • Worldwide burning of fossil fuels accounts for most of the other 80 percent.
NITROGEN CYCLE IMPACTS • Human activities may release large amounts of nitrogen compounds into the water or the air • Sewage treatment plants release dissolved nitrogen compounds into streams and rivers • Excess fertilizer may run off into nearby streams and ponds producing high levels of nitrogen and phosphates causing rapid growth of algae in the water, a condition called eutrophication • As the algae die, bacteria decomposing them can use up so much of the oxygen in the water that there is no longer enough to support other organisms.
NITROGEN CYCLE IMPACTS • Smokestacks and automobile exhaust pipes release certain nitrogen and sulfur into the atmosphere where they combine with water, forming nitric and sulfuric acids • Precipitation that carries this acid back to Earth's surface is called acid rain. • The Clean Air Act has helped lessen the acid rain problem in the U.S., but precipitation in some areas is still acidic enough to cause damage.
WATER CYCLE IMPACTS • Transpiration from dense tropical forests is a primary way that fresh water returns to the atmosphere • Tropical deforestation greatly reduces the amount of water vapor added to the atmosphere, changes precipitation patterns and affects ecosystems • Drawing water from rivers or underground aquifers also affects the water cycle • If the rate of water use is faster than the rate at which the water cycle can replace it, the river or aquifer may eventually run dry.
POLLUTION & BIOLOGICAL MAGNIFICATION • Pollution: The addition of substances to the environment that result in a negative effect • As organisms take in nutrients and water from the environment, they may also take in pollutants. • Some pollutants may be excreted, but others may accumulate in an organism's tissues.
PCBs from industrial waste can remain in the environment for a long time. A Great Lakes study found PCBs in tissues of organisms throughout the food web As higher trophic levels fed on each other, the PCBs accumulated in each predator's fatty tissues at even higher concentrations The process by which pollutants become more concentrated in successive trophic levels of a food web is called biological magnification. POLLUTION & BIOLOGICAL MAGNIFICATION
DAMAGE TO OZONE SHIELD • The ozone layer, a region of the atmosphere between 17 and 25 kilometers above Earth's surface, contains concentrations of ozone that absorb ultraviolet radiation, shielding organisms from its damaging effects. • Scientists have recorded the thinning of the ozone layer since the 1970s. A major contributor to the destruction of the layer are chlorofluorocarbons (CFCs) released from aerosol cans, refrigeration units, and certain manufacturing processes. These compounds destroy ozone
DAMAGE TO OZONE SHIELD • The consequences of ozone depletion for humans may include an increase in health problems such as skin cancer and cataracts due to increased ultraviolet radiation reaching Earth's surface • Nearly 200 nations, including the United States, are working to eliminate the use of ozone-destroying chemicals. For example, CFCs have been banned in many countries
Concept 36.5 CONSERVATION BIOLOGY CAN SLOW LOSS OF BIODIVERSITY
BIODIVERSITY • Biodiversity: encompasses the variety of life on Earth • Other aspects of biodiversity are the variety of ecosystems in the biosphere and the genetic variety among individuals within a species.
Why does biodiversity matter? • Many of the species in an ecosystem are interconnected. • Species depend on community interactions for food, shelter, and other needs. • If a key species disappears, other species—and the health of the whole ecosystem—may be affected
Why does biodiversity matter? • Organisms and ecosystems are a source of beauty and inspiration to many people. • People also rely on a great variety of organisms as sources of oxygen, food, clothing, and shelter. • Beyond providing these basics, biodiversity has aided the development of many medicines—In the U.S., 25%of all medicines contain substances originally derived from plants.
Why does biodiversity matter? • The possibility of identifying new products that could help humans is a strong argument for conserving biodiversity. • For example, some rain forest plants yield a medicines used to treat some types of cancer • Deforestation in rain forests threatens many rainforest species.
Threats to Biodiversity • In addition to the effects of pollution other threats to biodiversity include: • Habitat destruction • Introduction of non-native species • Overexploitation of species that already exist in ecosystems.
Habitat Destruction • As the human population grows, more land is needed for agriculture, roads, and communities. • Clearing land for these uses and for obtaining natural resources such as lumber, coal, and minerals may harm or even destroy natural communities. • If the organisms that require that habitat do not adapt or move to a new area, they will not survive.
Introduced Species • Introduced (non-native) species often prey on native species or compete with them for resources. • Many of the birds seen in cities are introduced species—starlings, house sparrows, and pigeons • These birds have compete with other native birds for nesting spots. • Losing nesting sites affected the ability of native species to reproduce, reducing their population.
Overexploitation • Overexploitation—the practice of harvesting or hunting to such a degree that the small number of remaining individuals may not be able to sustain the population. • Governments have placed strict limits on hunting and fishing certain species that have been threatened in this way • The ability of some protected species to rebound remains uncertain.
Overexploitation • Acategory of overexploitation includes animals that are poached, or hunted illegally, for economic reasons. • Often poachers sell animal products such as elephant tusks and rhinoceros horns for large amounts of money. • Other species are sold as exotic pets or decorative plants.
Conservation Biology Approaches:Focusing on Hot Spots • Many conservation biologists have focused their attention on biodiversity "hot spots." • Hot spots are small geographic areas (less than 1.5 percent of Earth's land surface) with high concentrations of species. • This tiny area is home to one third of all species of plants and vertebrates.
Conservation Biology Approaches:Focusing on Hot Spots • Biodiversity hot spots also tend to be hot spots of extinction. • They are a top priority demanding strong global conservation efforts. • Conservation biologists, lawmakers, and local communities are working to preserve areas of some hot spots as nature reserves. • They are exploring ways to manage these areas with the goal of meeting human needs, while still supporting the many other species living there.
Conservation Biology Approaches:Understanding an Organism's Habitat • Understanding the habitat requirements of a species can help biologists manage its existing habitat or create new habitat areas • By recognizing and protecting the key habitat factors, conservation biologists are giving threatened species a second chance. • By setting aside and protecting habitat areas, species are more likely to survive and continue to reproduce.
Conservation Biology Approaches:Balancing Demands for Resources • In many cases, a tug of war exists between efforts to save species and the economic and social needs of people. • Should a habitat be conserved in an effort to save a species if it means putting hundreds of people out of work? • Should work proceed on a new highway bridge making travel to work and school easier if it destroys the only remaining habitat of a species? • These are the types of questions raised when efforts are made to help protect biodiversity.
Conservation Biology Approaches:Balancing Demands for Resources • Politicians, townspeople, and conservation biologists can reach resolution to these questions by reviewing scientific data, weighing costs and benefits, looking for alternative solutions, and casting their votes.
Conservation Biology Approaches:Planning for a Sustainable Future • One way for nations to help protect ecosystems is to establish zoned reserves. • A zoned reserve includes areas of land that are relatively undisturbed by humans, surrounded by areas that are minimally impacted by humans called buffer zones. • The small Central American nation of Costa Rica has become a world leader in establishing zoned reserves. • The Costa Rican government set aside eight zoned reserves with the goal of maintaining at least 80 percent of its natural species.
Although humans live in the buffer zones, destructive environmental practices such as massive logging, large-scale single-crop agriculture, and extensive mining are discouraged. The zoned reserves encourage long-term ecosystem conservation through a balance of human needs and habitat preservation. Conservation Biology Approaches:Planning for a Sustainable Future .
Sustainable Development • Many nations, scientific organizations, and private foundations are working toward a goal of sustainable development—developing natural resources so that they can renew themselves and be available for the future. • People practicing sustainable development can continue to farm food and harvest timber while still protecting biodiversity. • A forest corridor through farmland may be left to connect two parts of an ecosystem, preventing habitat fragmentation. Timber may be harvested selectively, with only mature trees taken, instead of cutting down all the vegetation in an area.
Sustainable Development • Sustainable development depends on the continued research and applications of basic ecology and conservation biology. • The challenge for individuals and nations is to find a way to meet the needs of Earth's human population, while conserving ecosystems and resources for the planet's other populations as well.