Understanding Ecosystems: Energy Flow and Matter Cycling

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. Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling • Ecosystem ecologists view ecosystems • As transformers of energy and processors of matter

6. 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

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

8. 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

9. Nutrients cycle within an ecosystem

10. Decomposition • Decomposition • Connects all trophic levels

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

12. 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

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

14. The Global Energy Budget • 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

15. 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

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

17. 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 90 Desert and semidesert scrub 3.5 Tropical rain forest 2,200 22 3.3 2.9 Savanna 900 7.9 9.1 2.7 Cultivated land 600 Boreal forest (taiga) 9.6 2.4 800 1.8 Temperate grassland 600 5.4 Woodland and shrubland 700 1.7 3.5 Tundra 0.6 1.6 140 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 Swamp and marsh 2,000 2.3 Lake and stream 0.4 250 0.3 0 10 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0 5 10 15 20 25 Key Percentage of Earth’s net primary production Average net primary production (g/m2/yr) (a) (b) Percentage of Earth’s surface area 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 (c)

18. 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

19. Primary Production in Marine and Freshwater Ecosystems • In marine and freshwater ecosystems • Both light and nutrients are important in controlling primary production

20. Light Limitation • The depth of light penetration • Affects primary production throughout the photic zone of an ocean or lake

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

22. 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

23. EXPERIMENT Pollution from duck farms concentrated near Moriches Bay adds both nitrogen and phosphorus 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 Coast of Long Island, New York.The numbers on the map indicate the data collection stations. Atlantic Ocean 2 Figure 54.6 • Nutrient enrichment experiments • Confirmed that nitrogen was limiting phytoplankton growth in an area of the ocean

24. 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 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. CONCLUSION Figure 54.6

25. Table 54.1 • Experiments in another ocean region • Showed that iron limited primary production

26. The addition of large amounts of nutrients to lakes • Has a wide range of ecological impacts

27. 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

28. 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

29. The contrast between wet and dry climates • Can be represented by a measure called actual evapotranspiration

30. 3,000 Tropical forest 2,000 Net primary production (g/m2/yr) Temperate forest 1,000 Mountain coniferous forest Desert shrubland Temperate grassland Arctic tundra 0 500 1,000 1,500 Actual evapotranspiration (mm H2O/yr) 0 Figure 54.8 • Actual evapotranspiration • Is the amount of water annually transpired by plants and evaporated from a landscape • Is related to net primary production

31. EXPERIMENT Over the summer of 1980, researchers added phosphorus to some experimental plots in the salt marsh, nitrogento other plots, and both phosphorus and nitrogen to others. Some plots were left unfertilized as controls. Adding nitrogen (N) boosts net primary production. RESULTS 300 N  P 250 200 Live, above-ground biomass (g dry wt/m2) N only 150 100 Control P only 50 0 July August 1980 June Experimental plots receiving just phosphorus (P) do not outproduce the unfertilized control plots. CONCLUSION These nutrient enrichment experiments confirmed that nitrogen was the nutrient limiting plant growth in this salt marsh. Figure 54.9 • On a more local scale • A soil nutrient is often the limiting factor in primary production

32. 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

33. 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

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

35. 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%

36. 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

37. Pyramids of Biomass • One important ecological consequence of low trophic efficiencies • Can be represented in a biomass pyramid

38. 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

39. 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

40. 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

41. 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

42. 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

43. The Green World Hypothesis • According to the green world hypothesis • Terrestrial herbivores consume relatively little plant biomass because they are held in check by a variety of factors

44. Figure 54.15 • Most terrestrial ecosystems • Have large standing crops despite the large numbers of herbivores

45. 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

46. 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

47. 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

48. 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

49. All elements • Cycle between organic and inorganic reservoirs

50. 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