(8) Chapter 54

1. (8) Chapter 54 Ecosystems (生態系統) Ecology (生態學)

2. Key Concepts • Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling (生態系統強調能量流通與化學循環) • Concept 54.2: Physical and chemical factors limit primary production in ecosystems (物理與化學因子限制生態系統的初級生產量) • Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient (不同食性階層的能量轉移效率低於20%) • Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem (生物與地質化學過程生態系統有機與無機間的營養) • Concept 54.5: The human population is disrupting chemical cycles throughout the biosphere (人類族群破壞生物圈的化學循環)

3. Overview: Ecosystems, Energy, and Matter • An ecosystem consists of all the organisms living in a community as well as all the abiotic factors(非生物因子) with which they interact • Ecosystems can range from a microcosm (微宇宙), such as an aquarium (水族館) to a large area such as a lake or forest • An aquarium is an ecosystem bounded by glass Figure 54.1

4. Regardless of an ecosystem’s size (不論生態系統的尺度大小) • Its dynamics involve two main processes: energy flow and chemical cycling(能量流通與化學循環) • Energy flows through ecosystems • While matter cycles (物質循環) within them

5. Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling (生態系生態學強調能量流通與化學循環) • Ecosystem ecologists view ecosystems as • Transformers of energy (能量的轉換機器) • processors of matter (物質的加工機器)

6. Ecosystems and Physical Laws (物理定律) • The laws of physics and chemistry apply to ecosystems (物理與化學定律適用於生態系統) • Particularly in regard to the flow of energy. Two laws of thermodynamics govern energy transformations in organism and all other collections of matter • The first law of thermodynamics: energy can be transferred and transformed, but it cannot be created or destroyed (The principle of conservation of energy，能量守恆) • The second law of thermodynamics: every energy transfer or transformation increases the disorder (entropy) of the universe. Energy conversions cannot be completely efficient; some energy is always lost as heat in any conversion process • Energy is conserved, but degraded to heat during ecosystem processes (能量不滅，但是在生態系統變遷過程能量轉化為熱量)

7. Trophic Relationships(不同營養階層的關係) • Nutrients cycle within an ecosystem • Decomposition (分解作用) • Connects all trophic levels(聯繫所有營養階層) • Energy and nutrients pass from primary producers (autotrophs) 初級生產者(自營生物) • To primary consumers (herbivores食草動物/草食者) and then to secondary consumers (carnivores食肉動物/肉食者)

8. 生態系統中的能量流通與化學循環 • Energy flows through an ecosystem entering as light and exiting as heat 微生物及 其它碎食者 三級消費者 Tertiary consumers Microorganisms and other detritivores 次級消費者 Secondary consumers Detritus 碎屑 初級消費者 Primary consumers 初級生產者 Primary producers Key Heat Sun light Chemical cycling Energy flow Figure 54.2

9. Figure 54.3 • Detritivores (碎食生物/碎食者), mainly bacteria and fungi, recycle essential chemical elements • By decomposing organic material and transferring the chemical elements in inorganic forms to abiotic reservoirs, i.e. returning elements to inorganic reservoirs

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11. Concept 54.2: Physical and chemical factors limit primary production in ecosystems • Primary production (初級生產力) in an ecosystem • Is the amount of light energy converted to chemical energy by autotrophs during a given time period • Ecosystem Energy Budgets(生態系的能量預算) • The extent of photosynthetic production sets the spending limit for the energy budget of the entire ecosystem

12. The Global Energy Budget (全球的能量預算) • The amount of solar radiation reaching the surface of the Earth • Limits the photosynthetic output of ecosystems • Only a small fraction of solar energy • Actually strikes photosynthetic organisms

13. Gross and Net Primary Production (GPP &NPP) • Total primary production in an ecosystem • Is known as that ecosystem’s gross primary production(GPP)(總體初級生產力是所有初級生產力的總和) • Not all of this production • Is stored as organic material in the growing plants • Net primary production (NPP)(淨初級生產力) • Is equal to GPP minus the energy used by the primary producers for respiration (R) NPP=GPP-R • Only NPP • Is available to consumers

14. 125 Open ocean 24.4 65.0 360 Continental shelf 5.2 5.6 1,500 Estuary 0.3 1.2 Algal beds and reefs 2,500 0.1 0.9 Upwelling zones 0.1 500 0.1 Extreme desert, rock, sand, ice 3.0 4.7 0.04 0.9 Desert and semidesert scrub 90 3.5 2,200 22 3.3 Tropical rain forest 2.9 900 7.9 Savanna 9.1 2.7 600 Cultivated land 9.6 2.4 800 Boreal forest (taiga) 1.8 600 5.4 Temperate grassland 700 1.7 Woodland and shrubland 3.5 0.6 1.6 140 Tundra Tropical seasonal forest 1,600 7.1 1.5 Temperate deciduous forest 1,200 1.3 4.9 1,300 Temperate evergreen forest 1.0 3.8 0.4 2,000 2.3 Swamp and marsh 0.4 250 0.3 Lake and stream 0 10 20 30 40 50 60 0 5 10 15 20 25 0 500 1,000 1,500 2,000 2,500 Key Percentage of Earth’s net primary production Average net primary production (g/m2/yr) Percentage of Earth’s surface area (c) (a) (b) Marine Terrestrial Figure 54.4a–c Freshwater (on continents) • Different ecosystems vary considerably in their net primary production and in their contribution to the total NPP on Earth

15. North Pole 60N 30N Equator 30S 60S Figure 54.5. Regional annual net primary production for earth. The image is based on data, such as chlorophyll density by satellite. (Low) lighter violet→blue→green→yellow→orange→dark red (High) South Pole 120W 180 0 60E 120E 180 60W • Overall, terrestrial ecosystems(陸域生態系統) contribute about two-thirds (2/3) of global NPP and marine ecosystems about one-third (1/3)

16. Primary Production in Marine and Freshwater Ecosystems (海洋與淡水生態系的初級生產力) • In marine and freshwater ecosystems • Both light and nutrients are important in controlling primary production • Light Limitation (光線限制) • The depth of light penetration affects primary production throughout the photic zone of an ocean or lake • Nutrient Limitation (養份限制) • More than light, nutrients limit primary production, both in different geographic regions of the ocean and in lakes

17. A limiting nutrient (限制性養份) is the element that must be added • In order for production to increase in a particular area • Nitrogen (N) and phosphorous ( P) • Are typically the nutrients that most often limit marine production

18. Nutrient enrichment experiments confirmed that nitrogen (N) was limiting phytoplankton growth in an area of the ocean Experiment: Pollution from duck farms concentrated near Moriches Bay adds both nitrogen (N) and phosphorus (P) to the coastal water off Long Island. Researchers cultured the phytoplankton Nannochloris atomus with water collected from several bays. 30 21 Long Island 19 Shinnecock Bay 15 5 11 4 Moriches Bay Great South Bay 2 Atlantic Ocean Coast of Long Island, New York. The numbers on the map indicate the data collection stations. Figure 54.6

19. Results: Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of phosphate (PO43) did not induce algal growth (b). Ammonium enriched Phytoplankton 30 8 8 Phosphate enriched 7 7 Unenriched control Inorganic phosphorus 24 6 6 Phytoplankton (millions of cells/mL) Inorganic phosphorus (g atoms/L) 5 5 18 4 4 Phytoplankton (millions of cells per mL) 3 3 12 2 2 1 1 6 0 0 2 4 5 11 30 15 19 21 0 Station number Starting algal density 2 4 5 11 30 15 19 21 Great South Bay Moriches Bay Shinnecock Bay Station number (a) Phytoplankton biomass and phosphorus concentration (b) Phytoplankton response to nutrient enrichment Conclusion: Since adding phosphorus, which was already in rich supply, had no effect on Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem. Figure 54.6

20. Table 54.1 • Experiments in another ocean region showed that iron (Fe) limited primary production

21. Figure 54.7 • The addition of large amounts of nutrients to lakes • Has a wide range of ecological impacts (生態衝擊) • In some areas, sewage runoff • Has caused eutrophication of lakes (湖泊優養化), which can lead to the eventual loss of most fish species from the lakes

22. Primary Production in Terrestrial and Wetland Ecosystems(陸域及溼地生態系的初級生產力) • In terrestrial and wetland ecosystems climatic factors • Such as temperature and moisture, affect primary production on a large geographic scale(大的地理尺度) • The contrast between wet and dry climates • Can be represented by a measure called actual evapotranspiration

23. Actual evapotranspiration (蒸發散作用) • Is the amount of water annually transpired by plants and evaporated from a landscape • Is related to net primary production 3,000 Tropical forest (熱帶雨林) 2,000 Net primary production (g/m2/yr) Temperate forest (溫帶雨林) 1,000 Mountain coniferous forest (高山針葉林) Desert shrubland Temperate grassland (溫帶草原) Arctic tundra (極地苔原) 0 500 1,000 1,500 0 Actual evapotranspiration (mm H2O/yr) Figure 54.8

24. On a more local scale (地區性尺度) • A soil nutrient is often the limiting factor in primary production(土壤營養通常是初級生產力的限制因子) Over the summer of 1980, researchers added phosphorus (P) to some experimental plots in the salt marsh, nitrogen (N) to other plots, and both phosphorus (P) and nitrogen (N) to others. Some plots were left unfertilized as controls. EXPERIMENT RESULTS 300 Adding nitrogen (N) boosts net primaryproduction. N  P 250 200 N only 150 Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots. 100 Live, above-ground biomass (g dry wt/m2) Control 50 0 P only June July August 1980 Figure 54.9 These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh. CONCLUSION

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26. Concept 54.3: Energy transfer between trophic levels is usually less than 20% efficient • The secondary production of an ecosystem • Is the amount of chemical energy in consumers’ food that is converted to their own new biomass during a given period of time

27. Plant material eaten by caterpillar 200 J Cellular respiration 67 J 100 J Feces 33 J Growth (new biomass) Production Efficiency • When a caterpillar feeds on a plant leaf • Only about one-sixth (1/6) of the energy in the leaf is used for secondary production (次級生產) Figure 54.10

28. The production efficiency of an organism • Is the fraction of energy stored in food that is not used for respiration

29. Trophic Efficiency and Ecological Pyramids • Trophic efficiency (營養層級效應) • Is the percentage of production transferred from one trophic level to the next • Usually ranges from 5% to 20%

30. Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers 10,000 J 1,000,000 J of sunlight Pyramids of Net Production (淨生產力金字塔) • This loss of energy with each transfer in a food chain can be represented by a pyramid of net production 三級消費者 次級消費者 初級消費者 初級生產者 Figure 54.11

31. Pyramids of Biomass (生物量金字塔) • One important ecological consequence of low trophic efficiencies (低營養階層效率) • Can be represented in a biomass pyramid

32. Trophic level 營養階層 Dry weight (g/m2) Tertiary consumers 1.5 三級消費者 Secondary consumers 11 次級消費者 37 Primary consumers 初級消費者 809 Primary producers 初級生產者 (a) 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. Biomass pyramids (生物能量塔) • Most biomass pyramids show a sharp decrease at successively higher trophic levels (高營養階層) Figure 54.12a

33. Dry weight (g/m2) Trophic level Primary consumers (zooplankton浮游動物) 21 Primary producers (phytoplankton浮游植物) 4 (b) 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). • Certain aquatic ecosystems (水域生態系) have inverted biomass pyramids Figire 54.12b

34. Pyramids of Numbers (數量金字塔) • A pyramid of numbers represents the number of individual organisms in each trophic level (數量金字塔代表各營養層級的個體數目) Number of individual organisms Trophic level Tertiary consumers 3 Secondary consumers 354,904 Primary consumers 708,624 Primary producers 5,842,424 Figure 54.13

35. The dynamics of energy flow through ecosystems have important implications for the human population • Eating meat is a relatively inefficient way of tapping photosynthetic production • Worldwide agriculture could successfully feed many more people if humans all fed more efficiently, eating only plant material Secondary consumers Trophic level Primary consumers Primary producers Figure 54.14

36. The Green World Hypothesis (綠色世界假說) • According to the green world hypothesis • Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors • Most terrestrial ecosystems(陸域生態系) • Have large standing crops despite the large numbers of herbivores(草食動物) Figure 54.15

37. 綠色世界假說 • The green world hypothesis proposes several factors that keep herbivores in check • Plants have defenses against herbivores • Nutrients, not energy supply, usually limit herbivores • Abiotic factors(非生物因子) limit herbivores • Intraspecific competition(種內競爭) can limit herbivore numbers • Interspecific interactions (種間互動) check herbivore densities

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39. Concept 54.4: Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem • Life on Earth • Depends on the recycling of essential chemical elements • Nutrient circuits that cycle matter through an ecosystem • Involve both biotic and abiotic components and are often called biogeochemical cycles (生物地質化學循環)

40. A General Model of Chemical Cycling(化學循環) • Gaseous forms of carbon (C), oxygen (O), sulfur (S), and nitrogen (N) • Occur in the atmosphere and cycle globally (全球性循環) • Lessmobile elements, including phosphorous (P), potassium (K), and calcium (Ca) • Cycle on a more local level (地區性或區域性循環)

41. Nutrient cycling (營養循環) • A general model of nutrient cycling (營養循環) • Includes the main reservoirs of elements and the processes that transfer elements between reservoirs • All elements cycle between organic and inorganic reservoirs Reservoir a Reservoir b Organic materials available as nutrients Organic materials unavailable as nutrients Fossilization Living organisms, detritus Coal, oil, peat Respiration, decomposition, excretion Assimilation, photosynthesis Burning of fossil fuels Reservoir d Reservoir c Inorganic materials unavailable as nutrients Inorganic materials available as nutrients Weathering, erosion Minerals in rocks Atmosphere, soil, water Formation of sedimentary rock Figure 54.16

42. Biogeochemical Cycles (生物地質化學循環) • The water cycle and the carbon cycle (水循環及碳循環) THE CARBON CYCLE THE WATER CYCLE CO2 in atmosphere Transport over land Photosynthesis Solar energy Cellular respiration Net movement of water vapor by wind Precipitation over land Precipitation over ocean Evaporation from ocean Burning of fossil fuels and wood Evapotranspiration from land Higher-level consumers Primary consumers Percolation through soil Carbon compounds in water Detritus Runoff and groundwater Decomposition Figure 54.17

43. Water moves in a global cycle (全球循環) • Driven by solar energy (太陽能) • The carbon cycle (碳循環) • Reflects the reciprocal processes of photosynthesis and cellular respiration (反應光合作用與呼吸作用的相反過程)

44. THE PHOSPHORUS CYCLE THE NITROGEN CYCLE N2 in atmosphere Rain Weathering of rocks Plants Geologic uplift Assimilation Runoff Denitrifying bacteria Consumption NO3 Sedimentation Nitrogen-fixing bacteria in root nodules of legumes Plant uptake of PO43 Decomposers Nitrifying bacteria Soil Nitrification Leaching 滲漏作用 Ammonification NO2  NH3 NH4+ Nitrogen-fixing soil bacteria Nitrifying bacteria Decomposition Figure 54.17 Nitrogen cycle (N) and the phosphorous cycle (P) • The nitrogen cycle and the phosphorous cycle (氮循環及磷循環)

45. Most of the nitrogen cycling in natural ecosystems • Involves local cycles between organisms and soil or water • The phosphorus cycle • Is relatively localized • The rates at which nutrients cycle in different ecosystems • Are extremely variable, mostly as a result of differences in rates of decomposition

46. Decomposition and Nutrient Cycling Rates • Decomposers (detritivores, 分解者) play a key role • In the general pattern of chemical cycling Consumers Producers Biotic (生物性) Decomposers Nutrients available to producers Abiotic reservoir Abiotic (非生物性) Geologic processes Figure 54.18

47. Vegetation and Nutrient Cycling: The Hubbard Brook Experimental Forest • Nutrient cyclingis strongly regulated by vegetation(植被強烈地調節營養循環) • Long-term ecological research (LTER) projects (長期生態研究) • Monitor ecosystem dynamics over relatively long periods of time • The Hubbard Brook Experimental Forest • Has been used to study nutrient cycling in a forest ecosystem since 1963

48. The research team constructed a dam on the site • To monitor water and mineral loss (a) 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. Figure 54.19a

49. (b) One watershed was clear cut to study the effects of the lossof vegetation on drainage and nutrient cycling. Figure 54.19b • In one experiment, the trees in one valley were cut down and the valley was sprayed with herbicides (除草劑)

50. 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 80.0 Deforested 60.0 40.0 20.0 Nitrate concentration in runoff (mg/L) Completion of tree cutting 4.0 Control 3.0 2.0 1.0 0 1967 1965 1966 1968 (c) The concentration of nitrate in runoff from the deforested watershed was 60 times greater than in a control (unlogged) watershed. Figure 54.19c