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. 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

4. 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

5. Trophic Relationships • Energy and nutrients pass from primary producers (autotrophs) • To primary consumers (herbivores) and then to secondary consumers (carnivores)

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

7. Decomposition • Decomposition • Connects all trophic levels

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

9. 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

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

11. 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

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

13. Nutrient Limitation • More than light, nutrients limit primary production • Both in different geographic regions of the ocean and in lakes

14. A limiting nutrient is the element that must be added • In order for production to increase in a particular area • Nitrogen and phosphorous • Are typically the nutrients that most often limit marine production

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

16. 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 geographic scale

17. 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

18. Trophic Efficiency and Ecological Pyramids • Trophic efficiency • Is the percentage of production transferred from one trophic level to the next • Usually ranges from 5% to 20%

19. 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

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. 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 limit herbivores • Intraspecific competition can limit herbivore numbers • Interspecific interactions check herbivore densities

23. 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

24. 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

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

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

27. 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

28. 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

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

30. 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

31. Contamination of Aquatic Ecosystems • The critical load for a nutrient • Is the amount of that nutrient that can be absorbed by plants in an ecosystem without damaging it

32. When excess nutrients are added to an ecosystem, the critical load is exceeded • And the remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

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

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

35. 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

36. 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

37. 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

38. 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

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

40. 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

41. 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

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

43. 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

44. 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

45. 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

46. (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