Chapter 54

1. Chapter 54 Ecosystems

2. . • Overview: Ecosystems, Energy, and Matter • An ecosystem consists of all the organisms living in a community • As well as all the abiotic factors with which they interact

3. . • Ecosystems can range from a microcosm, such as an aquarium • To a large area such as a lake or forest Figure 54.1

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. Ecosystems and Physical Laws • The laws of physics and chemistry apply to ecosystems • Particularly in regard to the flow of energy • Energy is conserved • But degraded to heat during ecosystem processes

6. Tertiary consumers Microorganisms and other detritivores Secondary consumers Primary consumers Detritus Primary producers Heat Key Chemical cycling Sun Energy flow Figure 54.2 Trophic Relationships • Energy flows through an ecosystem • Entering as light and exiting as heat

7. Figure 54.3 . • Detritivores, mainly bacteria and fungi, recycle essential chemical elements • By decomposing organic material and returning elements to inorganic reservoirs

8. . • 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

9. Ecosystem Energy Budgets • The extent of photosynthetic production • Sets the spending limit for the energy budget of the entire ecosystem

10. Gross and Net Primary Production • Total primary production in an ecosystem • Is known as that ecosystem’s gross primary production (GPP) • Not all of this production • Is stored as organic material in the growing plants

11. . • Net primary production (NPP) • Is equal to GPP minus the energy used by the primary producers for respiration • Only NPP • Is available to consumers

12. North Pole 60N 30N Equator 30S 60S South Pole 120W 180 0 60E 120E 180 60W Figure 54.5 . • Overall, terrestrial ecosystems • Contribute about two-thirds of global NPP and marine ecosystems about one-third

13. Figure 54.7 Eutrophication • In some areas, sewage runoff • Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes

14. . • 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

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

16. Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers 10,000 J Figure 54.11 1,000,000 J of sunlight Pyramids of Production • This loss of energy with each transfer in a food chain • Can be represented by a pyramid of net production

17. Dry weight (g/m2) Trophic level Tertiary consumers 1.5 Secondary consumers 11 37 Primary consumers Primary producers 809 (a) Most biomass pyramids show a sharp decrease in biomass at successively higher trophic levels, as illustrated by data froma bog at Silver Springs, Florida. Figure 54.12a . • Most biomass pyramids • Show a sharp decrease at successively higher trophic levels

18. Dry weight (g/m2) Trophic level 21 Primary consumers (zooplankton) Primary producers (phytoplankton) 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). Figire 54.12b . • Certain aquatic ecosystems • Have inverted biomass pyramids

19. Trophic level Number of individual organisms Tertiary consumers 3 Secondary consumers 354,904 Primary consumers 708,624 Primary producers 5,842,424 Figure 54.13 Pyramids of Numbers • A pyramid of numbers • Represents the number of individual organisms in each trophic level

20. . • 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

21. Trophic level Secondary consumers Primary consumers Primary producers . • Worldwide agriculture could successfully feed many more people • If humans all fed more efficiently, eating only plant material Figure 54.14

22. A General Model of Chemical Cycling • Gaseous forms of carbon, oxygen, sulfur, and nitrogen • Occur in the atmosphere and cycle globally • Less mobile elements, including phosphorous, potassium, and calcium • Cycle on a more local level

23. 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 Atmosphere, soil, water Minerals in rocks Formation of sedimentary rock Figure 54.16 . • A general model of nutrient cycling • Includes the main reservoirs of elements and the processes that transfer elements between reservoirs

24. 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 Biogeochemical Cycles • The water cycle and the carbon cycle

25. Water moves in a global cycle • Driven by solar energy • The carbon cycle • Reflects the reciprocal processes of photosynthesis and cellular respiration

26. THE PHOSPHORUS CYCLE THE NITROGEN CYCLE N2 in atmosphere Rain Plants Weathering of rocks Geologic uplift Runoff Assimilation Denitrifying bacteria Consumption NO3 Sedimentation Nitrogen-fixing bacteria in root nodules of legumes Plant uptake of PO43 Decomposers Nitrifying bacteria Soil Nitrification Leaching Ammonification NO2  NH3 NH4+ Nitrogen-fixing soil bacteria Nitrifying bacteria Decomposition Figure 54.17 • The nitrogen cycle and the phosphorous cycle

27. Most of the nitrogen cycling in natural ecosystems • Involves local cycles between organisms and soil or water • The phosphorus cycle • Is relatively localized

28. Consumers Producers Decomposers Nutrients available to producers Abiotic reservoir Geologic processes Figure 54.18 Decomposition and Nutrient Cycling Rates • Decomposers (detritivores) play a key role • In the general pattern of chemical cycling

29. 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 . • 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

30. Concept 54.5: The human population is disrupting chemical cycles throughout the biosphere • As the human population has grown in size • Our activities have disrupted the trophic structure, energy flow, and chemical cycling of ecosystems in most parts of the world

31. Nutrient Enrichment • In addition to transporting nutrients from one location to another • Humans have added entirely new materials, some of them toxins, to ecosystems

32. Figure 54.20 Agriculture and Nitrogen Cycling • Agriculture constantly removes nutrients from ecosystems • That would ordinarily be cycled back into the soil

33. . • Nitrogen is the main nutrient lost through agriculture • Thus, agriculture has a great impact on the nitrogen cycle • Industrially produced fertilizer is typically used to replace lost nitrogen • But the effects on an ecosystem can be harmful

34. Sewage runoff contaminates freshwater ecosystems • Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems

35. Acid Precipitation • Combustion of fossil fuels • Is the main cause of acid precipitation

36. 4.6 4.3 4.6 4.3 4.6 4.1 4.3 4.6 Europe Figure 54.21 North America . • North American and European ecosystems downwind from industrial regions • Have been damaged by rain and snow containing nitric and sulfuric acid

37. Field pH 5.3 5.2–5.3 5.1–5.2 5.0–5.1 4.9–5.0 4.8–4.9 4.7–4.8 4.6–4.7 4.5–4.6 4.4–4.5 4.3–4.4 Figure 54.22 4.3 • By the year 2000 • The entire contiguous United States was affected by acid precipitation

38. . • Environmental regulations and new industrial technologies • Have allowed many developed countries to reduce sulfur dioxide emissions in the past 30 years

39. Toxins in the Environment • Humans release an immense variety of toxic chemicals • Including thousands of synthetics previously unknown to nature • One of the reasons such toxins are so harmful • Is that they become more concentrated in successive trophic levels of a food web

40. Herring gull eggs 124 ppm Lake trout 4.83 ppm Concentration of PCBs Smelt 1.04 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Figure 54.23 . • In biological magnification • Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower

41. . • In some cases, harmful substances • Persist for long periods of time in an ecosystem and continue to cause harm

42. Atmospheric Carbon Dioxide • One pressing problem caused by human activities • Is the rising level of atmospheric carbon dioxide

43. 1.05 390 0.90 380 0.75 370 Temperature 0.60 360 0.45 350 CO2 concentration (ppm) Temperature variation (C) 0.30 340 CO2 0.15 330 0 320 0.15 310  0.30  0.45 300 1975 1980 1985 1990 1995 2000 2005 1960 1965 1970 Year Figure 54.24 Rising Atmospheric CO2 • Due to the increased burning of fossil fuels and other human activities • The concentration of atmospheric CO2 has been steadily increasing

44. Figure 54.25 How Elevated CO2 Affects Forest Ecology: The FACTS-I Experiment • The FACTS-I experiment is testing how elevated CO2 • Influences tree growth, carbon concentration in soils, and other factors over a ten-year period

45. The Greenhouse Effect and Global Warming • The greenhouse effect is caused by atmospheric CO2 • But is necessary to keep the surface of the Earth at a habitable temperature

46. . • Increased levels of atmospheric CO2 are magnifying the greenhouse effect • Which could cause global warming and significant climatic change

47. Depletion of Atmospheric Ozone • Life on Earth is protected from the damaging effects of UV radiation • By a protective layer or ozone molecules present in the atmosphere

48. 350 300 250 Ozone layer thickness (Dobson units) 200 150 100 50 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Year (Average for the month of October) Figure 54.26 • Satellite studies of the atmosphere • Suggest that the ozone layer has been gradually thinning since 1975

49. Chlorine from CFCs interacts with ozone (O3),forming chlorine monoxide (ClO) and oxygen (O2). 1 Chlorine atoms O2 Chlorine O3 ClO O2 Sunlight causes Cl2O2 to break down into O2and free chlorine atoms. The chlorine atoms can begin the cycle again. 3 ClO Cl2O2 Two ClO molecules react, forming chlorine peroxide (Cl2O2). 2 Sunlight Figure 54.27 • The destruction of atmospheric ozone • Probably results from chlorine-releasing pollutants produced by human activity

50. (b) October 2000 (a) October 1979 • Scientists first described an “ozone hole” • Over Antarctica in 1985; it has increased in size as ozone depletion has increased Figure 54.28a, b