1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 54 Ecosystems

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trophic Relationships Energy and nutrients pass from primary producers (autotrophs) – To primary consumers (herbivores) and then to secondary consumers (carnivores)

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy flows through an ecosystem – Entering as light and exiting as heat Figure 54.2 Microorganisms and other detritivores Detritus Primary producers Primary consumers Secondary consumers Tertiary consumers Heat Sun Key Chemical cycling Energy flow

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition – Connects all trophic levels

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Detritivores, mainly bacteria and fungi, recycle essential chemical elements – By decomposing organic material and returning elements to inorganic reservoirs Figure 54.3

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecosystem Energy Budgets The extent of photosynthetic production – Sets the spending limit for the energy budget of the entire ecosystem

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nutrient Limitation More than light, nutrients limit primary production – Both in different geographic regions of the ocean and in lakes

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In some areas, sewage runoff – Has caused eutrophication of lakes, which can lead to the eventual loss of most fish species from the lakes Figure 54.7

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyramids of Production This loss of energy with each transfer in a food chain – Can be represented by a pyramid of net production Figure 54.11 Tertiary consumers Secondary consumers Primary consumers Primary producers 1,000,000 J of sunlight 10 J 100 J 1,000 J 10,000 J

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Worldwide agriculture could successfully feed many more people – If humans all fed more efficiently, eating only plant material Figure 54.14 Trophic level Secondary consumers Primary consumers Primary producers

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water moves in a global cycle – Driven by solar energy The carbon cycle – Reflects the reciprocal processes of photosynthesis and cellular respiration

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most of the nitrogen cycling in natural ecosystems – Involves local cycles between organisms and soil or water The phosphorus cycle – Is relatively localized

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Decomposition and Nutrient Cycling Rates Decomposers (detritivores) play a key role – In the general pattern of chemical cycling Figure 54.18 Consumers Producers Nutrients available to producers Abiotic reservoir Geologic processes Decomposers

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sewage runoff contaminates freshwater ecosystems – Causing cultural eutrophication, excessive algal growth, which can cause significant harm to these ecosystems

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Acid Precipitation Combustion of fossil fuels – Is the main cause of acid precipitation

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings North American and European ecosystems downwind from industrial regions – Have been damaged by rain and snow containing nitric and sulfuric acid Figure 54.21 4.6 4.3 4.1 4.3 4.6 4.3 Europe North America

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings By the year 2000 – The entire contiguous United States was affected by acid precipitation Figure 54.22 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  4.3

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In biological magnification – Toxins concentrate at higher trophic levels because at these levels biomass tends to be lower Figure 54.23 Concentration of PCBs Herring gull eggs 124 ppm Zooplankton 0.123 ppm Phytoplankton 0.025 ppm Lake trout 4.83 ppm Smelt 1.04 ppm

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Atmospheric Carbon Dioxide One pressing problem caused by human activities – Is the rising level of atmospheric carbon dioxide

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rising Atmospheric CO 2 Due to the increased burning of fossil fuels and other human activities – The concentration of atmospheric CO 2 has been steadily increasing Figure 54.24 CO 2 concentration (ppm) 390 380 370 360 350 340 330 320 310 300 196019651970 1975198019851990199520002005 1.05 0.90 0.75 0.60 0.45 0.30 0.15 0  0.15  0.30  0.45 Temperature variation (  C) Temperature CO 2 Year

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Greenhouse Effect and Global Warming The greenhouse effect is caused by atmospheric CO 2 – But is necessary to keep the surface of the Earth at a habitable temperature

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Increased levels of atmospheric CO 2 are magnifying the greenhouse effect – Which could cause global warming and significant climatic change

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Satellite studies of the atmosphere – Suggest that the ozone layer has been gradually thinning since 1975 Figure 54.26 Ozone layer thickness (Dobson units) Year (Average for the month of October) 350 300 250 200 150 100 50 0 19551960196519701975198019851990199520002005

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The destruction of atmospheric ozone – Probably results from chlorine-releasing pollutants produced by human activity Figure 54.27 1 2 3 Chlorine from CFCs interacts with ozone (O 3 ), forming chlorine monoxide (ClO) and oxygen (O 2 ). Two ClO molecules react, forming chlorine peroxide (Cl 2 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 ChlorineO3O3 O2O2 ClO Cl 2 O 2 O2O2 Chlorine atoms

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Scientists first described an “ozone hole” – Over Antarctica in 1985; it has increased in size as ozone depletion has increased Figure 54.28a, b (a) October 1979 (b) October 2000