Chapter 54. Ecosystems. PowerPoint Lectures for Biology, Seventh Edition. Neil Campbell and Jane Reece

Transcription

1 Chapter 54 Ecosystems PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece

2 Overview: Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest

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4 Regardless of an ecosystem s size, its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems while matter cycles within them

5 Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling Ecologists view ecosystems as transformers of energy and processors of matter

6 Ecosystems and Physical Laws Laws of physics and chemistry apply to ecosystems, particularly energy flow Energy is conserved but degraded to heat during ecosystem processes

7 Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) and then to secondary consumers (carnivores) Energy flows through an ecosystem, entering as light and exiting as heat Nutrients cycle within an ecosystem

8 LE 54-2 Tertiary consumers Microorganisms and other detritivores Secondary consumers Detritus Primary consumers Primary producers Heat Key Chemical cycling Energy flow Sun

9 Decomposition Decomposition connects all trophic levels Detritivores, mainly bacteria and fungi, recycle essential chemical elements by decomposing organic material and returning elements to inorganic reservoirs

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11 Concept 54.2: Physical and chemical factors limit primary production in ecosystems Primary production in an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period

12 Ecosystem Energy Budgets The extent of photosynthetic production sets the spending limit for an ecosystem s energy budget

13 The Global Energy Budget The amount of solar radiation reaching the Earth s surface limits photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms

14 Gross and Net Primary Production Total primary production is known as the ecosystem s gross primary production (GPP) Net primary production (NPP) is GPP minus energy used by primary producers for respiration Only NPP is available to consumers Ecosystems vary greatly in net primary production and contribution to the total NPP on Earth

15 LE 54-4 Open ocean Continental shelf Estuary Algal beds and reefs Upwelling zones Extreme desert, rock, sand, ice Desert and semidesert scrub Tropical rain forest Savanna Cultivated land Boreal forest (taiga) Temperate grassland Woodland and shrubland Tundra Tropical seasonal forest Temperate deciduous forest Temperate evergreen forest Swamp and marsh Lake and stream Key Marine Terrestrial Freshwater (on continents) ,500 2,500 2,200 1,600 1,200 1,300 2, ,000 1,500 2,000 2,500 Percentage of Earth s surface area Average net primary production (g/m 2 /yr) Percentage of Earth s net primary production

16 Overall, terrestrial ecosystems contribute about two-thirds of global NPP Marine ecosystems contribute about one-third

17 LE 54-5 North Pole 60 N 30 N Equator 30 S 60 S South Pole W 60 W 0 60 E 120 E 180

18 Primary Production in Marine and Freshwater Ecosystems In marine and freshwater ecosystems, both light and nutrients control primary production

19 Light Limitation Depth of light penetration affects primary production in the photic zone of an ocean or lake

20 Nutrient Limitation More than light, nutrients limit primary production in geographic regions of the ocean and in lakes

21 A limiting nutrient is the element that must be added for production to increase in an area Nitrogen and phosphorous are typically the nutrients that most often limit marine production Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean

22 LE Shinnecock Bay Moriches Bay 2 Atlantic Ocean Coast of Long Island, New York Phytoplankton (millions of cells/ml) Phytoplankton Inorganic phosphorus 5 Great South Bay Station number Moriches Bay Inorganic phosphorus (µm atoms/l) Shinnecock Bay Phytoplankton biomass and phosphorus concentration Phytoplankton (millions of cells per ml) Ammonium enriched Phosphate enriched Unenriched control 0 Starting algal density Station number Phytoplankton response to nutrient enrichment

23 Experiments in another ocean region showed that iron limited primary production

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25 The addition of large amounts of nutrients to lakes has a wide range of ecological impacts In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species

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27 Primary Production in Terrestrial and Wetland Ecosystems In terrestrial and wetland ecosystems, climatic factors such as temperature and moisture affect primary production on a large scale Actual evapotranspiration can represent the contrast between wet and dry climates Actual evapotranspiration is the water annually transpired by plants and evaporated from a landscape It is related to net primary production

28 LE 54-8 Net primary production (g/m 2 /yr) 3,000 2,000 1, Desert shrubland Arctic tundra Temperate forest Mountain coniferous forest Temperate grassland Tropical forest 500 1,000 1,500 Actual evapotranspiration (mm/yr)

29 On a more local scale, a soil nutrient is often the limiting factor in primary production

30 LE June July N + P N only Control P only August 1980 Live, above-ground biomass (g dry wt/m 2 )

31 Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time

32 Production Efficiency When a caterpillar feeds on a leaf, only about onesixth of the leaf s energy is used for secondary production An organism s production efficiency is the fraction of energy stored in food that is not used for respiration

33 LE Plant material eaten by caterpillar 200 J Feces 100 J 33 J 67 J Cellular respiration Growth (new biomass)

34 Trophic Efficiency and Ecological Pyramids Trophic efficiency is the percentage of production transferred from one trophic level to the next It usually ranges from 5% to 20%

35 Pyramids of Production A pyramid of net production represents the loss of energy with each transfer in a food chain

36 LE Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers 10,000 J 1,000,000 J of sunlight

37 Pyramids of Biomass In a biomass pyramid, each tier represents the dry weight of all organisms in one trophic level Most biomass pyramids show a sharp decrease at successively higher trophic levels

38 LE 54-12a Trophic level Dry weight (g/m 2 ) Tertiary consumers Secondary consumers Primary consumers Primary producers Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data from a bog at Silver Springs, Florida.

39 Certain aquatic ecosystems have inverted biomass pyramids: Primary consumers outweigh the producers

40 LE 54-12b Trophic level Dry weight (g/m 2 ) Primary consumers (zooplankton) Primary producers (phytoplankton) 21 4 In some aquatic ecosystems, such as the English Channel, a small standing crop of primary producers (phytoplankton) supports a larger standing crop of primary consumers (zooplankton).

41 Pyramids of Numbers A pyramid of numbers represents the number of individual organisms in each trophic level

42 LE Trophic level Number of individual organisms Tertiary consumers Secondary consumers Primary consumers Primary producers 3 354, ,624 5,842,424

43 Dynamics of energy flow in ecosystems have important implications for the human population Eating meat is a relatively inefficient way of tapping photosynthetic production Worldwide agriculture could feed many more people if humans ate only plant material

44 LE Trophic level Secondary consumers Primary consumers Primary producers

45 The Green World Hypothesis Most terrestrial ecosystems have large standing crops despite the large numbers of herbivores

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47 The green world hypothesis proposes several factors that keep herbivores in check: Plant defenses Limited availability of essential nutrients Abiotic factors Intraspecific competition Interspecific interactions

48 Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem Life depends on recycling chemical elements Nutrient circuits in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

49 A General Model of Chemical Cycling Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally Less mobile elements such as phosphorus, potassium, and calcium cycle on a more local level A model of nutrient cycling includes main reservoirs of elements and processes that transfer elements between reservoirs All elements cycle between organic and inorganic reservoirs

50 LE Reservoir a Reservoir b Organic materials available as nutrients Living organisms, detritus Fossilization Organic materials unavailable as nutrients Coal, oil, peat Assimilation, photosynthesis Respiration, decomposition, excretion Burning of fossil fuels Reservoir c Inorganic materials available as nutrients Weathering, erosion Reservoir d Inorganic materials unavailable as nutrients Atmosphere, soil, water Formation of sedimentary rock Minerals in rocks

51 Biogeochemical Cycles In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors: 1. Each chemical s biological importance 2. Forms in which each chemical is available or used by organisms 3. Major reservoirs for each chemical 4. Key processes driving movement of each chemical through its cycle

52 LE 54-17a Solar energy Transport over land Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Evapotranspiration from land Precipitation over land Runoff and groundwater Percolation through soil

53 LE 54-17b CO 2 in atmosphere Photosynthesis Cellular respiration Burning of fossil fuels and wood Carbon compounds in water Higher-level Primary consumers consumers Detritus Decomposition

54 LE 54-17c N 2 in atmosphere Assimilation Nitrogen-fixing bacteria in root nodules of legumes Decomposers Ammonification Nitrification NO 3 Denitrifying bacteria Nitrifying bacteria NH 3 Nitrogen-fixing soil bacteria NH 4 + Nitrifying bacteria NO 2

55 LE 54-17d Rain Geologic uplift Weathering of rocks Runoff Plants Sedimentation Soil Leaching Plant uptake of PO 4 3 Consumption Decomposition

56 Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role in the general pattern of chemical cycling Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition

57 LE Consumers Producers Decomposers Nutrients available to producers Abiotic reservoir Geologic processes

58 Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest Vegetation strongly regulates nutrient cycling Research projects monitor ecosystem dynamics over long periods The Hubbard Brook Experimental Forest has been used to study nutrient cycling in a forest ecosystem since 1963

59 The research team constructed a dam on the site to monitor loss of water and minerals

60 LE Concrete dams and weirs built across streams at the bottom of watersheds enabled researchers to monitor the outflow of water and nutrients from the ecosystem. One watershed was clear cut to study the effects of the loss of vegetation on drainage and nutrient cycling. Nitrate concentration in runoff (mg/l) Completion of tree cutting Deforested Control The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed.

61 In one experiment, the trees in one valley were cut down, and the valley was sprayed with herbicides

62 Net losses of water and minerals were studied and found to be greater than in an undisturbed area These results showed how human activity can affect ecosystems

63 Concept 54.5: The human population is disrupting chemical cycles throughout the biosphere As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems

64 Nutrient Enrichment In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems

65 Agriculture and Nitrogen Cycling Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

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67 Contamination of Aquatic Ecosystems Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem When excess nutrients are added to an ecosystem, the critical load is exceeded Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems

68 Acid Precipitation Combustion of fossil fuels is the main cause of acid precipitation North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid

69 LE Europe North America

70 By the year 2000, acid precipitation affected the entire contiguous United States Environmental regulations and new technologies have allowed many developed countries to reduce sulfur dioxide emissions

71 LE Field ph <

72 Toxins in the Environment Humans release many toxic chemicals, including synthetics previously unknown to nature In some cases, harmful substances persist for long periods in an ecosystem One reason toxins are harmful is that they become more concentrated in successive trophic levels In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

73 LE Herring gull eggs 124 ppm Concentration of PCBs Smelt 1.04 ppm Lake trout 4.83 ppm Zooplankton ppm Phytoplankton ppm

74 Atmospheric Carbon Dioxide One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide

75 Rising Atmospheric CO 2 Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO 2 has been steadily increasing

76 How Elevated CO 2 Affects Forest Ecology: The FACTS-I Experiment The FACTS-I experiment is testing how elevated CO 2 influences tree growth, carbon concentration in soils, and other factors over a ten-year period

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78 The Greenhouse Effect and Global Warming The greenhouse effect caused by atmospheric CO 2 keeps Earth s surface at a habitable temperature Increased levels of atmospheric CO 2 are magnifying the greenhouse effect, which could cause global warming and climatic change

79 Depletion of Atmospheric Ozone Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere Satellite studies suggest that the ozone layer has been gradually thinning since 1975

80 LE Ozone layer thickness (Dobson units) Year (Average for the month of October)

81 Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity

82 LE Chlorine atoms Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (CIO) and oxygen (O 2 ). O 2 Chlorine O 3 CIO O 2 Sunlight causes Cl 2 O 2 to break down into O 2 and free chlorine atoms. The chlorine atoms can begin the cycle again. Sunlight Cl 2 O 2 CIO Two CIO molecules react, forming chlorine peroxide (Cl 2 O 2 ).

83 Scientists first described an ozone hole over Antarctica in 1985; it has increased in size as ozone depletion has increased

84 LE October 1979 October 2000