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42 Ecosystems and Energy.

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1 42 Ecosystems and Energy

2 Overview: Cool Ecosystem
An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact An example is the unusual community of organisms, including chemoautotrophic bacteria, living below a glacier in Antarctica 2

3 Figure 42.1 Figure 42.1 Why is this Antarctic ice blood red? 3

4 Ecosystems range from a microcosm, such as space under a fallen log or desert spring, to a large area, such as a lake or forest 4

5 Figure 42.2 Figure 42.2 A desert spring ecosystem 5

6 Energy flows through ecosystems, whereas matter cycles within them
Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems, whereas matter cycles within them 6

7 Concept 42.1: Physical laws govern energy flow and chemical cycling in ecosystems
Ecologists study the transformations of energy and matter within ecosystems 7

8 Conservation of Energy
Laws of physics and chemistry apply to ecosystems, particularly energy flow The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed Energy enters an ecosystem as solar radiation, is transformed into chemical energy by photosynthetic organisms, and is dissipated as heat 8

9 The second law of thermodynamics states that every exchange of energy increases the entropy of the universe In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat Continuous input from the sun is required to maintain energy flow in Earth’s ecosystems 9

10 Conservation of Mass The law of conservation of mass states that matter cannot be created or destroyed Chemical elements are continually recycled within ecosystems In a forest ecosystem, most nutrients enter as dust or solutes in rain and are carried away in water Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products 10

11 Ecosystems can be sources or sinks for particular elements
If a mineral nutrient’s outputs exceed its inputs it will limit production in that system 11

12 Energy, Mass, and Trophic Levels
Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source Heterotrophs depend on the biosynthetic output of other organisms 12

13 Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores) 13

14 Prokaryotes and fungi are important detritivores
Detritivores, or decomposers, are consumers that derive their energy from detritus, nonliving organic matter Prokaryotes and fungi are important detritivores Decomposition connects all trophic levels; detritivores are fed upon by secondary and tertiary consumers 14

15 Figure 42.3 Figure 42.3 Fungi decomposing a dead tree 15

16 Sun Key Chemical cycling Heat Energy flow Primary producers Primary
Figure 42.4 Sun Key Chemical cycling Heat Energy flow Primary producers Primary consumers Detritus Figure 42.4 An overview of energy and nutrient dynamics in an ecosystem Microorganisms and other detritivores Secondary and tertiary consumers 16

17 Concept 42.2: Energy and other limiting factors control primary production in ecosystems
In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period In a few ecosystems, chemoautotrophs are the primary producers 17

18 Ecosystem Energy Budgets
The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget 18

19 The Global Energy Budget
The amount of solar radiation reaching Earth’s surface limits the photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength 19

20 Gross and Net Production
Total primary production is known as the ecosystem’s gross primary production (GPP) GPP is measured as the conversion of chemical energy from photosynthesis per unit time 20

21 Net primary production (NPP) is GPP minus energy used by primary producers for “autotrophic respiration” (Ra) NPP is expressed as Energy per unit area per unit time (J/m2  yr), or Biomass added per unit area per unit time (g/m2  yr) NPP = GPP − Ra 21

22 NPP is the amount of new biomass added in a given time period
Only NPP is available to consumers Standing crop is the total biomass of photosynthetic autotrophs at a given time Ecosystems vary greatly in NPP and contribution to the total NPP on Earth 22

23 Technique 80 Snow Clouds 60 Vegetation Percent reflectance 40 Soil 20
Figure 42.5 Technique 80 Snow Clouds 60 Vegetation Percent reflectance 40 Soil 20 Figure 42.5 Research method: determining primary production with satellites Liquid water 400 600 800 1,000 1,200 Visible Near-infrared Wavelength (nm) 23

24 Tropical rain forests, estuaries, and coral reefs are among the most productive ecosystems per unit area Marine ecosystems are relatively unproductive per unit area but contribute much to global net primary production because of their volume Video: Oscillatoria 24

25 Net primary production (kg carbon/m2 • yr)
Figure 42.6 Net primary production (kg carbon/m2 • yr) 3 2 1 Figure 42.6 Global net primary production 25

26 Net ecosystem production (NEP) is a measure of the total biomass accumulation during a given period
NEP is gross primary production minus the total respiration of all organisms (producers and consumers) in an ecosystem (RT) NEP = GPP − RT 26

27 NEP is estimated by comparing the net flux of CO2 and O2 in an ecosystem, two molecules connected by photosynthesis The release of O2 by a system is an indication that it is also storing CO2 27

28 Primary Production in Aquatic Ecosystems
In marine and freshwater ecosystems, both light and nutrients control primary production 28

29 Light Limitation Depth of light penetration affects primary production in the photic zone of an ocean or lake About half the solar radiation is absorbed in the first 15 m of water, and only 5–10% reaches a depth of 75 m 29

30 Nutrient Limitation More than light, nutrients limit primary production in geographic regions of the ocean and in lakes A limiting nutrient is the element that must be added for production to increase in an area Nitrogen and phosphorous are the nutrients that most often limit marine production Nutrient enrichment experiments confirmed that nitrogen was limiting phytoplankton growth off the shore of Long Island, New York 30

31 (millions of cells per mL) Phytoplankton density
Figure 42.7 Results 30 Ammonium enriched Phosphate enriched 24 Unenriched control 18 (millions of cells per mL) Phytoplankton density 12 Figure 42.7 Inquiry: Which nutrient limits phytoplankton production along the coast of Long Island? 6 A B C D E F G Collection site 31

32 Experiments in the Sargasso Sea in the subtropical Atlantic Ocean showed that iron limited primary production 32

33 Table 42.1 Table 42.1 Nutrient enrichment experiment for Sargasso Sea samples 33

34 Upwelling of nutrient-rich waters in parts of the oceans contributes to regions of high primary production The addition of large amounts of nutrients to lakes has a wide range of ecological impacts 34

35 This has led to the use of phosphate-free detergents
In some areas, sewage runoff has caused eutrophication of lakes, which can lead to loss of most fish species In lakes, phosphorus limits cyanobacterial growth more often than nitrogen This has led to the use of phosphate-free detergents 35

36 Primary Production in Terrestrial Ecosystems
In terrestrial ecosystems, temperature and moisture affect primary production on a large scale Primary production increases with moisture 36

37 Net annual primary production (above ground, dry g/m2 • yr)
Figure 42.8 1,400 1,200 1,000 Net annual primary production (above ground, dry g/m2 • yr) 800 600 400 Figure 42.8 A global relationship between net primary production and mean annual precipitation for terrestrial ecosystems 200 20 40 60 80 100 120 140 160 180 200 Mean annual precipitation (cm) 37

38 It is affected by precipitation, temperature, and solar energy
Actual evapotranspiration is the water transpired by plants and evaporated from a landscape It is affected by precipitation, temperature, and solar energy Actual evapotranspiration can be used as a predictor of net primary production 38

39 Nutrient Limitations and Adaptations That Reduce Them
On a more local scale, a soil nutrient is often the limiting factor in primary production In terrestrial ecosystems, nitrogen is the most common limiting nutrient Phosphorus can also be a limiting nutrient, especially in older soils 39

40 Various adaptations help plants access limiting nutrients from soil
Some plants form mutualisms with nitrogen-fixing bacteria Many plants form mutualisms with mycorrhizal fungi; these fungi supply plants with phosphorus and other limiting elements Roots have root hairs that increase surface area Many plants release enzymes that increase the availability of limiting nutrients 40

41 Concept 42.3: Energy transfer between trophic levels is typically only 10% efficient
Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time 41

42 Production Efficiency
When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production Net secondary production is the energy stored in biomass An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration Production efficiency = Net secondary production × 100% Assimilation of primary production 42

43 secondary production)
Figure 42.9 Plant material eaten by caterpillar 200 J 67 J Cellular respiration Figure 42.9 Energy partitioning within a link of the food chain 100 J Feces 33 J Not assimilated Growth (new biomass; secondary production) Assimilated 43

44 Figure 42.9a Figure 42.9a Energy partitioning within a link of the food chain (part 1: photo) 44

45 Insects and microorganisms have efficiencies of 40% or more
Birds and mammals have efficiencies in the range of 13% because of the high cost of endothermy Insects and microorganisms have efficiencies of 40% or more 45

46 Trophic Efficiency and Ecological Pyramids
Trophic efficiency is the percentage of production transferred from one trophic level to the next, usually about 10% Trophic efficiencies take into account energy lost through respiration and contained in feces, as well as the energy stored in unconsumed portions of the food source Trophic efficiency is multiplied over the length of a food chain 46

47 Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer
A pyramid of net production represents the loss of energy with each transfer in a food chain 47

48 Tertiary consumers 10 J Secondary consumers 100 J Primary consumers
Figure 42.10 Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers Figure An idealized pyramid of net production 10,000 J 1,000,000 J of sunlight 48

49 In a biomass pyramid, each tier represents the standing crop (total dry mass of all organisms) in one trophic level Most biomass pyramids show a sharp decrease at successively higher trophic levels 49

50 Dry mass (g/m2) 1.5 11 37 809 Dry mass (g/m2) 21 4
Figure 42.11 Trophic level Dry mass (g/m2) Tertiary consumers 1.5 Secondary consumers 11 Primary consumers 37 Primary producers 809 (a) Most ecosystems (data from a Florida bog) Trophic level Dry mass (g/m2) Figure Pyramids of biomass (standing crop) Primary consumers (zooplankton) 21 Primary producers (phytoplankton) 4 (b) Some aquatic ecosystems (data from the English Channel) 50

51 Turnover time is the ratio of the standing crop biomass to production
Certain aquatic ecosystems have inverted biomass pyramids: producers (phytoplankton) are consumed so quickly that they are outweighed by primary consumers Turnover time is the ratio of the standing crop biomass to production Turnover time = Standing crop (g/m2) Production (g/m2  day) 51

52 Dynamics of energy flow in ecosystems have important implications for the human population
Eating meat is a relatively inefficient way of tapping photosynthetic production Worldwide agriculture could feed many more people if humans ate only plant material 52

53 Concept 42.4: Biological and geochemical processes cycle nutrients and water in ecosystems
Life depends on recycling chemical elements Decomposers (detritivores) play a key role in the general pattern of chemical cycling 53

54 Decomposition and Nutrient Cycling Rates
Rates at which nutrients cycle in different ecosystems vary greatly, mostly as a result of differing rates of decomposition The rate of decomposition is controlled by temperature, moisture, and nutrient availability 54

55 Mean annual temperature (°C) R
Figure 42.12 Experiment Ecosystem type Results Arctic 80 Subarctic 70 Boreal Temperate 60 R U A K O Grassland 50 Q T Percent of mass lost G J P Mountain 40 S D N F 30 C I M L M 20 A H B,C D B E P 10 G T H,I S E,F N L O U −15 −10 −5 5 10 15 J Figure Inquiry: How does temperature affect litter decomposition in an ecosystem? K Q Mean annual temperature (°C) R 55

56 Experiment Ecosystem type Arctic Subarctic Boreal Temperate A
Figure 42.12a Experiment Ecosystem type Arctic Subarctic Boreal Temperate A Grassland G Mountain M B,C D P T H,I E,F Figure 42.12a Inquiry: How does temperature affect litter decomposition in an ecosystem? (part 1: experiment) S N L O U J K Q R 56

57 Mean annual temperature (°C)
Figure 42.12b Results 80 70 U 60 R O K Q 50 T Percent of mass lost J P 40 S D N F 30 C I M L 20 A H B E G 10 Figure 42.12b Inquiry: How does temperature affect litter decomposition in an ecosystem? (part 2: results) −15 −10 −5 5 10 15 Mean annual temperature (°C) 57

58 Decomposition is slow in anaerobic muds
Rapid decomposition results in relatively low levels of nutrients in the soil For example, in a tropical rain forest, material decomposes rapidly, and most nutrients are tied up in trees and other living organisms Cold and wet ecosystems store large amounts of undecomposed organic matter, as decomposition rates are low Decomposition is slow in anaerobic muds 58

59 Biogeochemical Cycles
Nutrient cycles in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally Less mobile elements include phosphorus, potassium, and calcium These elements cycle locally in terrestrial systems but more broadly when dissolved in aquatic systems 59

60 Each step in a chemical cycle can be driven by biological or purely physical processes
60

61 Water is essential to all organisms
The Water Cycle Water is essential to all organisms Liquid water is the primary physical phase in which water is used The oceans contain 97% of the biosphere’s water; 2% is in glaciers and polar ice caps, and 1% is in lakes, rivers, and groundwater Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater Animation: Carbon Cycle 61

62 The water cycle Movement over land by wind Precipitation over land
Figure 42.13a Movement over land by wind Precipitation over land Precipitation over ocean Evaporation from ocean Evapotranspiration from land Figure 42.13a Exploring water and nutrient cycling (part 1: water) Percolation through soil Runoff and groundwater The water cycle 62

63 Carbon-based organic molecules are essential to all organisms
The Carbon Cycle Carbon-based organic molecules are essential to all organisms Photosynthetic organisms convert CO2 to organic molecules that are used by heterotrophs Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks 63

64 CO2 is taken up by the process of photosynthesis and released into the atmosphere through cellular respiration Volcanic activity and the burning of fossil fuels also contribute CO2 to the atmosphere 64

65 The carbon cycle CO2 in atmosphere Photosynthesis Photo- synthesis
Figure 42.13b CO2 in atmosphere Photosynthesis Photo- synthesis Cellular respiration Burning of fossil fuels and wood Phyto- plankton Consumers Figure 42.13b Exploring water and nutrient cycling (part 2: carbon) Consumers Decomposition The carbon cycle 65

66 Nitrogen is a component of amino acids, proteins, and nucleic acids
The Nitrogen Cycle Nitrogen is a component of amino acids, proteins, and nucleic acids The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3− for uptake by plants, via nitrogen fixation by bacteria 66

67 Denitrification converts NO3− back to N2
Organic nitrogen is decomposed to NH4+ by ammonification, and NH4+ is decomposed to NO3− by nitrification Denitrification converts NO3− back to N2 67

68 The nitrogen cycle N2 in atmosphere Reactive N gases Industrial
Figure 42.13c N2 in atmosphere Reactive N gases Industrial fixation Denitrification N fertilizers Fixation Runoff Dissolved organic N NO3− Terrestrial cycling N2 NO3− NH4 Aquatic cycling Denitri- fication Figure 42.13c Exploring water and nutrient cycling (part 3: nitrogen) Decomposition and sedimentation Decom- position Assimilation NO3− Fixation in root nodules Uptake of amino acids Ammoni- fication Nitrification NH4 The nitrogen cycle 68

69 The nitrogen cycle N2 in atmosphere Reactive N gases Industrial
Figure 42.13ca N2 in atmosphere Reactive N gases Industrial fixation Denitrification N fertilizers Fixation Runoff Dissolved organic N NO3− NO3− NH4 Figure 42.13ca Exploring water and nutrient cycling (part 3a: full nitrogen cycle) Aquatic cycling Decomposition and sedimentation The nitrogen cycle 69

70 The nitrogen cycle Terrestrial N2 cycling Denitri- fication
Figure 42.13cb Terrestrial cycling N2 Denitri- fication Assimilation Decom- position NO3− Fixation in root nodules Uptake of amino acids Figure 42.13cb Exploring water and nutrient cycling (part 3b: terrestrial nitrogen cycle) Ammoni- fication Nitrification NH4 The nitrogen cycle 70

71 Phosphate (PO43−) is the most important inorganic form of phosphorus
The Phosphorus Cycle Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP Phosphate (PO43−) is the most important inorganic form of phosphorus The largest reservoirs are sedimentary rocks of marine origin, the soil, oceans, and organisms Phosphate binds with soil particles, and movement is often localized 71

72 The phosphorus cycle Wind-blown dust Geologic uplift Weathering
Figure 42.13d Wind-blown dust Geologic uplift Weathering of rocks Runoff Consumption Decomposition Plant uptake of PO43− Plankton Dissolved PO43− Uptake Leaching Figure 42.13d Exploring water and nutrient cycling (part 4: phosphorus) Sedimentation Decomposition The phosphorus cycle 72

73 Case Study: Nutrient Cycling in the Hubbard Brook Experimental Forest
The Hubbard Brook Experimental Forest has been used to study nutrient cycling in a forest ecosystem since 1963 The research team constructed a dam on the site to monitor loss of water and minerals They found that 60% of the precipitation exits through streams and 40% is lost by evapotranspiration Most mineral nutrients were conserved in the system 73

74 Nitrate concentration
Figure 42.14 (a) Concrete dam and weir (b) Clear-cut watershed 80 Deforested 60 40 Figure Nutrient cycling in the Hubbard Brook Experimental Forest: an example of long-term ecological research 20 Nitrate concentration in runoff (mg/L) Completion of tree cutting 4 3 Control 2 1 1965 1966 1967 1968 (c) Nitrate in runoff from watersheds 74

75 (a) Concrete dam and weir
Figure 42.14a Figure 42.14a Nutrient cycling in the Hubbard Brook Experimental Forest: an example of long-term ecological research (part 1: dam and weir) (a) Concrete dam and weir 75

76 (b) Clear-cut watershed
Figure 42.14b Figure 42.14b Nutrient cycling in the Hubbard Brook Experimental Forest: an example of long-term ecological research (part 2: clear-cut watershed) (b) Clear-cut watershed 76

77 Nitrate concentration
Figure 42.14c 80 Deforested 60 40 20 Nitrate concentration in runoff (mg/L) Completion of tree cutting 4 3 Control 2 1 Figure 42.14c Nutrient cycling in the Hubbard Brook Experimental Forest: an example of long-term ecological research (part 3: nitrate runoff) 1965 1966 1967 1968 (c) Nitrate in runoff from watersheds 77

78 In one experiment, the trees in one valley were cut down, and the valley was sprayed with herbicides
78

79 Net losses of water were 3040% greater in the deforested site than in the undisturbed (control) site Nutrient loss was also much greater in the deforested site compared with the undisturbed site For example, nitrate levels increased 60 times in the outflow of the deforested site These results showed that the amount of nutrients leaving a forest ecosystem is controlled mainly by plants 79

80 Concept 42.5: Restoration ecologists help return degraded ecosystems to a more natural state
Given enough time, biological communities can recover from many types of disturbances Restoration ecology seeks to initiate or speed up the recovery of degraded ecosystems Two key strategies are bioremediation and augmentation of ecosystem processes 80

81 (a) In 1991, before restoration In 2000, near the completion of
Figure 42.15 Figure A gravel and clay mine site in New Jersey before and after restoration (a) In 1991, before restoration In 2000, near the completion of restoration (b) 81

82 (a) In 1991, before restoration
Figure 42.15a Figure 42.15a A gravel and clay mine site in New Jersey before and after restoration (part 1: before) (a) In 1991, before restoration 82

83 (b) In 2000, near the completion of restoration
Figure 42.15b Figure 42.15b A gravel and clay mine site in New Jersey before and after restoration (part 2: after) (b) In 2000, near the completion of restoration 83

84 Bioremediation Bioremediation is the use of organisms to detoxify ecosystems The organisms most often used are prokaryotes, fungi, or plants These organisms can take up, and sometimes metabolize, toxic molecules For example, the bacterium Shewanella oneidensis can metabolize uranium and other elements to insoluble forms that are less likely to leach into streams and groundwater 84

85 soluble uranium (M) Concentration of
Figure 42.16 6 5 4 soluble uranium (M) Concentration of 3 2 1 50 100 150 200 250 300 350 400 Figure Bioremediation of groundwater contaminated with uranium at Oak Ridge National Laboratory, Tennessee Days after adding ethanol (a) Wastes containing uranium, Oak Ridge National Laboratory (b) Decrease in concentration of soluble uranium in groundwater 85

86 Wastes containing uranium, Oak Ridge National Laboratory (a)
Figure 42.16a Figure 42.16a Bioremediation of groundwater contaminated with uranium at Oak Ridge National Laboratory, Tennessee (part 1: photo) Wastes containing uranium, Oak Ridge National Laboratory (a) 86

87 soluble uranium (M) Concentration of
Figure 42.16b 6 5 4 soluble uranium (M) Concentration of 3 2 1 Figure 42.16b Bioremediation of groundwater contaminated with uranium at Oak Ridge National Laboratory, Tennessee (part 2: graph) 50 100 150 200 250 300 350 400 Days after adding ethanol Decrease in concentration of soluble uranium in groundwater (b) 87

88 Biological Augmentation
Biological augmentation uses organisms to add essential materials to a degraded ecosystem For example, nitrogen-fixing plants can increase the available nitrogen in soil For example, adding mycorrhizal fungi can help plants to access nutrients from soil 88

89 Restoration Projects Worldwide
The newness and complexity of restoration ecology require that ecologists consider alternative solutions and adjust approaches based on experience 89

90 Kissimmee River, Florida Succulent Karoo, South Africa
Figure 42.17 Kissimmee River, Florida Succulent Karoo, South Africa Figure Exploring restoration ecology worldwide Maungatautari, New Zealand Coastal Japan 90

91 Kissimmee River, Florida
Conversion of the Kissimmee River to a 90-km canal threatened many fish and wetland bird populations Filling 12 km of the canal has restored natural flow patterns to 24 km of the river, helping to foster a healthy wetland ecosystem 91

92 Kissimmee River, Florida
Figure 42.17a Figure 42.17a Exploring restoration ecology worldwide (part 1: Kissimmee River) Kissimmee River, Florida 92

93 Succulent Karoo, South Africa
Overgrazing by livestock has damaged vast areas of land in this region Restoration efforts have included revegetating the land and employing sustainable resource management 93

94 Succulent Karoo, South Africa
Figure 42.17b Figure 42.17b Exploring restoration ecology worldwide (part 2: Succulent Karoo) Succulent Karoo, South Africa 94

95 Maungatautari, New Zealand
Introduction of exotic mammals including weasels, rats, and pigs has threatened many native plant and animal species Restoration efforts include building fences around reserves to exclude introduced species 95

96 Maungatautari, New Zealand
Figure 42.17c Figure 42.17c Exploring restoration ecology worldwide (part 3: Maungatautari) Maungatautari, New Zealand 96

97 Coastal Japan Destruction of coastal seaweed and seagrass beds through development has threatened a variety of fishes and shellfish Restoration efforts include constructing suitable habitat, transplantation, and hand seeding 97

98 Figure 42.17d Figure 42.17d Exploring restoration ecology worldwide (part 4: Coastal Japan) Coastal Japan 98

99 Figure 42.UN01 Figure 42.UN01 Skills exercise: interpreting quantitative data in a table 99

100 Sun Key Chemical cycling Energy flow Heat Primary producers Primary
Figure 42.UN02 Sun Key Chemical cycling Energy flow Heat Primary producers Primary consumers Detritus Figure 42.UN02 Summary of key concepts: energy flow and chemical cycling Microorganisms and other detritivores Secondary and tertiary consumers 100

101 Tertiary consumers 10 J Secondary consumers 100 J Primary consumers
Figure 42.UN03 Tertiary consumers 10 J Secondary consumers 100 J Primary consumers 1,000 J Primary producers Figure 42.UN03 Summary of key concepts: trophic efficiency 10,000 J 1,000,000 J of sunlight 101


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