Ecosystems and Energy Flow

Ecosystems and Energy Flow - Ecosystems Ecosystems What is...

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Unformatted text preview: Ecosystems Ecosystems What is an ecosystem? Ecosystems are: Ecosystems self-contained self-contained assemblages of organisms that, together with their physical environments, move energy and nutrients among the component parts. parts. Ecosystems Ecosystems Ecosystem Ecosystem ecology focuses on energy flow and nutrient cycles as parts of a coordinated whole. whole. Ecosystems Ecosystems Advantages of the ecosystem concept: 1. Provides a mechanism for integrating Provides information from many different ecosystems. Organisms are assigned functional roles. functional Ecosystems Ecosystems 2. Easier to compare ecosystems Easier using the functional roles rather than taxonomic classifications. • For example we can compare nitrogen For cycles in tropical versus temperate versus boreal ecosystems. versus Ecosystems Ecosystems 3. Ecosystems can be modeled Ecosystems more easily than populations or communities in many cases. communities Ecosystems Ecosystems 4. The ecosystem approach has many The applications. Resource • Resource management (fisheries, • forestry) and pollution monitoring. Global scale problems need an Global ecosystem approach to be effective. Recall the First Two General Principles of Ecology Principles 1. Ecological systems function Ecological according to the laws of thermodynamics (Ecosystems). thermodynamics 2. The physical environment exerts a The controlling influence on the productivity of ecological systems (Ecosystems). (Ecosystems). Ecosystems: Energy Flow Begins with Primary Production Production Primary Production Solar radiation is the principle source of energy. energy. It arrives in a variety of wavelengths. Ecosystems: Primary Production Primary Only 400 to 700 nanometers are Only effective in photosynthesis. effective Solar radiation has dual properties: Solar 1. 1. 2. wave lengths particles (photons) Ecosystems: Primary Production Primary Photons of different wavelengths have Photons different energy values long wave lengths = less energy Short wave lengths = more energy Ecosystems: Primary Production Primary An Einstein (e) = energy content of An one mole of photons one 1e of red (0.7μ) llight = 42,000 ight 1e red calories calories 1e of blue (0.5μ) llight = 60,000 ight 1e blue calories calories Ecosystems: Primary Production Primary Gram calorie = amount of heat energy Gram needed to raise the temperature of 1g of water 1o C. of Most ecosystem units are in Most kilocalories =1,000 gram calories = 1g of food calorie. 1g Ecosystems: Primary Production Primary Energetic units are usually expressed as Energetic rates: kcal/m2/day. rates By contrast: Standing crop = an energy unit converted to a biomass equivalent at a given point in time (kg of carbon/m2) given Ecosystems: Primary Production Primary Rate of energy input via solar radiation: radiation: Amount of energy entering Earth’s Amount atmosphere is estimated at 15.3 X 108 atmosphere cal/m2per year or 15.3 X 105 kcal/m2 cal/m kcal/m year-1. year Ecosystems: Primary Production Primary Much of this energy is scattered by Much dust, used in heating the ground, water, and air and in evaporating water. Amount available to plants varies by Amount latitude and climate as we discussed latitude climate earlier. earlier. Ecosystems: Primary Production Primary Primary Production defined: The accumulation of energy by autotrophs (photosynthesis or autotrophs chemosynthesis) per unit area per unit time. unit Ecosystems: Secondary Production Secondary Secondary Production defined: The accumulation of energy by heterotrophs (herbivores, decomposers etc.) per unit area per unit time. unit Ecosystems: Primary Production Primary Gross production (GP) = total amount of energy accumulated at a trophic level. level. Net production (NP) = gross production minus losses due to respiration. respiration NP = GP - R Ecosystems: Primary Production Primary Net Production is the energy that will Net be stored in the ecosystem as stored biomass. biomass That is, when organisms accumulate That energy, this energy is stored as mass and we refer to it as biomass. biomass Ecosystems: Primary Production Primary Biomass serves as a handy measure of accumulated net production in an ecosystem. ecosystem. Ecosystems: Primary Production Primary Global Patterns of Net Production Global (Biomass): (Biomass): Terrestrial: 115 X 109 metric tons/year (67% of total) tons/year Aquatic: 55 X 109 metric tons/year (33% of total) (33% Ecosystems: Primary Production Primary Conclusion: Oceans cover 2/3 Oceans of Earth’s surface but only produce 1/3 of the Net Production. Production. Ecosystems: Primary Production Primary Ecosystems with low production (NP): Terrestrial: Deserts and Deserts Tundras, which make up 30% of which the land surface area of the world. world. Aquatic: Open Oceans, which Open which make up 90% of the total marine surface area. surface Ecosystems: Primary Production Primary Ecosystems with high production Ecosystems high (NP): (NP): Tropical Shallow wet forests aquatic areas (marshes, estuaries, coral marshes, reefs) reefs Terrestrial Net Production Terrestrial The limits to terrestrial net The terrestrial production in natural ecosystems are due to availabilities of: are 1. 2. 3. Temperature Moisture Light Light Ecosystems: Primary Production Primary The log of evapotranspiration The evapotranspiration predicts accurately the above ground biomass (NP) of terrestrial ecosystems. Evapotranspiration is defined as: The total amount of water vapor The returned to the atmosphere as a result of direct evaporation or plant transpiration transpiration Terrestrial Net Production Evapotranspiration is a surrogate for: for: moisture availability, moisture light and temperature. Ecosystems: Secondary Production Secondary Primary production predicts secondary production (herbivore secondary biomass, for example). biomass, Recall the Second Principle of Ecology Ecology The physical environment exerts a The controlling influence on the productivity of ecological systems (Ecosystems). (Ecosystems). Ecosystems: Primary Production Primary Although primary production is Although regulated in a similar fashion everywhere, there is a fundamental difference between terrestrial and terrestrial aquatic ecosystems. aquatic Ecosystems: Primary Production Primary Terrestrial ecosystem primary Terrestrial production is determined by moisture, light, and temperature (as measured by evapotranspiration). by Nutrient availability, especially P especially and N are the most important regulators of aquatic productivity. aquatic Ecosystems: Primary Production Primary In temperate freshwater lakes, In temperate seasonal fluctuations in NP are tied to the seasonal changes in temperature. These seasonal changes in turn affect These thermal stratification. This determines the availability of This nutrients in the surface waters where photosynthesis takes place. photosynthesis Ecosystems: Primary Production Primary Aquatic Ecosystems Aquatic These changes are driven by the fact These that the density of water varies with temperature. Warm water is less dense than cool Warm water. However, water reaches its However, maximum density at 4o C. maximum C. Ecosystems: Primary Production Primary Aquatic Ecosystems In the summer warm water stays near In the surface and cool water remains near the bottom of lakes. This produces thermal stratification. thermal In the winter, very cold water remains In at the surface, and the warmer, 4o at water sinks to the bottom. Ecosystems: Primary Production Primary Aquatic Ecosystems In the spring and fall there are times In when the lakes become isothermal. isothermal That is, temperatures are the same from top to bottom. This encourages mixing of nutrient This laden bottom water with oxygenated surface waters. Lake Productivity Lake Oligotrophic = A lake with low productivity; usually a young lake with few nutrients, often deep with clear water. water. Mesotrophic = A middle-aged lake with higher productivity and a higher nutrient level. nutrient Ecosystems: Ecosystems: Lake Productivity Eutrophic = An old lake or a lake heavily affected by pollutants. Very high nutrient levels; highly productive, but often poor in species. The term “cultural eutrophication” refers to lakes aging very quickly due to human pollutants. to Eutrophic versus Oligotrophic Lake Eutrophic Ecosystems: Primary Production Primary Productivity is often measured as Productivity changes in standing crop over a unit of time. of SCt+1= SCt + NPt-(t+1) – H – D NPt-(t+1) = NP in the time period t to t+1 H = losses due to herbivores D = llosses due to death and decomposition of osses plant parts plant Ecosystems: Primary Production Primary Photosynthetic Efficiency, PE PE = NP/PAR NP = Net Production = GP – R PAR = Photosynthetically Active PAR Radiation Radiation Gross versus Net Productivity in Some Crop Plants (kcal/m2/day) NP PE(%) PG (%) PAR GP Sugar Cane, Hawaii 4000 306 190 4.8 62 Maize, Israel 6000 405 190 3.2 47 Sugar Beets, England 2650 202 144 5.4 71 Respiration Losses Respiration GP – NP = R Sugar Cane: R = 306–190 =116 Kcal/m2/day Sugar 306–190 Maize: R= 405 – 190 = 215 Kcal/m2/day Maize: Sugar Beets: R= 202–144 = 58 Kcal/m2/day Sugar Respiration Losses Respiration Therefore, English sugar beets have Therefore, an NP that equals 75% of the other crops even with only 44% of the PAR of the maize in Israel, because the losses due to R are so low. losses low Respiration Losses Respiration In both homothermic and In heterothermic organisms: heterothermic Respiration losses increase with temperature. temperature. In many green plants: As As photosynthesis rates go up with temperature, so do respiration rates. temperature, Adaptations: Adaptations: High Temperatures and High Light Conditions Conditions At least three different photosynthetic At pathways have been evolved by plants, allowing them to adapt to different light and temperature regimes. regimes. These are C3, C4 and Crassulacean Acid Metabolism (CAM). Acid Atriplex patula Atriplex rosea Figure 7.1 Differences Among C3, C4, and CAM Plants Characteristic C3 Plants C4 Plants CAM Plants Light-saturation point 3000 - 6000 footcandles 8000 - 10000+ ? footcandles Optimum temperature 16o – 25o 40o – 50o 30o – 35o CO2 compensation 30 – 70 ppm 0 – 10 ppm 0 – 4 ppm Maximum photosynthetic rate 15 – 35 30 – 45 3 - 13 1 4 0.02 Photorespiration High Low Low Stomata Behavior Open day, closed night Open day, closed night Closed day, open night (mg CO2/dm2 leaf area/hr) Maximum growth rate (g/dm /day) 2 Ecosystems: Energy Budgets Energy Energy Budgets: Illustrate Illustrate where major energy drains are in natural and agricultural ecosystems. ecosystems. Ecosystems: Secondary Production Secondary Secondary production is higher in marine systems because a much higher fraction of photoysynthetic NP is consumed by animals in oceans than in terrestrial systems. Consumption efficiency averages 2550% (as high as 90%) in marine 50% systems, but is 5-10% in terrestrial forests. forests. Ecosystems: Secondary Production Secondary Secondary production is also higher production in tropical terrestrial ecosystems as compared to equivalent temperate systems. systems. The accumulation of dead organic The matter (litter) is highest in cold forests (especially Boreal forests). (especially Decomposition Decomposition Dead organic Dead matter (DOM) provides energy for decomposers of the detrital food chain. food Decomposition Decomposition Unless organic material is Unless accumulating (as it did during the previous geological eras, leading to the deposition of our fossil fuels), then… then… NP = Decomposition plus losses to herbivores herbivores Decomposition Decomposition During decomposition, During organic matter is reduced, ultimately to CO2 and H2O, and CO O, nutrients are released. nutrients “Decomposition” by Jessica Langley Decomposition Decomposition Without decomposition, supplies of Without essential nutrients would be locked up in organic matter and dwindle to the point that GP would decline even though solar radiation remained available. This actually happens in many This aquatic systems. aquatic Decomposition Decomposition 1. 2. Trends in litter (plant organic Trends litter matter) production and production and decomposition: decomposition Litter production is linked to NP. Litter production More in the tropics, least in deserts. More Litter accumulation, however, is accumulation however, highest in high latitude Boreal forests because of slow decomposition rates. decomposition Decomposition Decomposition 3. Litter is not uniform in composition. Litter The ratio of C/N determines the rate of decomposition. The higher the ratio decomposition The the slower the decomposition, because N is usually a rate limiting factor for decomposing organisms, just as it is for photosynthesis. Fresh litter has a high C/N ratio and decomposes slowly. C/N Different species have different C/N ratios and differences in secondary compounds. and Decomposition Decomposition 4. Cellulose The higher the The proportion of cellulose, woody fibers, lignin, and resins, the slower the decomposition. the Decomposition Decomposition 5. Very acidic or basic pHs also slow Very decomposition rates. Acid pHs are common in bogs, for example, leading to an accumulation of peat. peat. Peat Bog in Ireland Bog People from Ireland Bog Artifacts Shinrone Dress Gold beads and torques Decomposition Decomposition 6. Oxygen levels can also limit Oxygen decomposition, especially in aquatic environments. Anoxic conditions Anoxic are found in some soils, many lakes, and in ocean sediments. The Chesapeake Bay suffers from The anoxic zones due to pollution. anoxic Because of pollution there are even Because “dead zones” in the Gulf of Mexico. “dead Decomposition Decomposition Organic material is Organic ultimately broken down in its final stages by bacteria bacteria and fungi. and fungi Final degradation to Final carbon dioxide and water is carried out by these organisms, called the ultimate decomposers. ultimate Decomposition Decomposition However, a wide variety of organisms However, prepare the way for bacteria and fungi. These are called reducer-decomposers. These reducer-decomposers Decomposition Decomposition Red Spider Mite For example, plant For material is first processed by microarthropods, such as mites, spring-tails (Collembolans), as well as by nematodes, earth worms, millipedes and slugs. slugs. Earthworms Decomposition Decomposition Animal material is first attacked by Animal carrion flies, a wide variety of beetles, and carrion eaters such as crows, vultures and some mammals. vultures Decomposition Decomposition These reducer-decomposers shred, These reducer-decomposers tear and grind up the organic material, increasing its surface area and/or chemically processing the material in their guts. This improves oxygen penetration of This the organic material and opens up these tissues to ultimate decomposition by bacteria and fungi. decomposition Dermestid Beetles Cleaning a Skull: Used for conservation of skeletons. Decomposition Decomposition The result is that the rate of The decomposition by the ultimate decomposers is vastly increased once the surface area is increased. the Ecological Efficiencies Ecological Energy flow from one trophic level to Energy another is never 100% efficient. another Efficiencies allow ecologists to Efficiencies measure rates of energy transfer and make comparisons among ecosystems as well as estimate the number of tropic levels that can be supported. supported. Ecological Efficiencies Ecological As energy moves from one trophic As level to another, there are a number of stages where energy is dissipated of See the following diagram. Ecological Efficiencies Ecological At the end of the last step is the NP of At the new trophic level. the Recall that secondary production is Recall secondary the formation of heterotrophic biomass in terms of kcal/unit area/time. area/time. Ecological Efficiencies Ecological In a study of elephants In at Queen Elizabeth Park in Uganda, the plant NP was 747 kcal/m2/year. kcal/m Ecological Efficiencies Ecological Of that the elephants: Consumed 71.5 kcal/m2/year. Lost in urine and feces = 40.2 Assimilation = 31.3 Respiration = 30.96 NP2 = 0.34 kcal/m2/year NP1= 747 Kcal NP 747 675.5 (not consumed) consumed) Consumption = 71.5 Assimilation = 31.3 40.2 (feces) Respiration = 30.96 NP2 = 0.34 Kcal Ecological Efficiencies Ecological Standing crop estimated as 7.1 Standing kcal/m2/year. kcal/m /year. Ecological Efficiencies Ecological These figures allow us to examine three These efficiencies related to the movement of energy within a trophic level. energy 1. Photosynthetic efficiency PE = NP/PAR NP/PAR PAR = photosynthetically active radiation. For example, the cattail marsh had a PE of 2.2%. Photosynthetic Efficiencies Photosynthetic Japanese Rice Japanese Scots Pine, Britain Scots Beech Forest, Denmark Beech Sugar Cane, Java Sugar Sugar Cane, Hawaii Sugar Maize, Israel Maize, Sugar Beets, England Sugar = = = = = = = 2.2% 2.2% 2.4% 2.4% 2.5% 2.5% 1.9% 1.9% 4.8% 4.8% 3.2% 3.2% 5.4% 5.4% Secondary Production: Secondary Assimilation Efficiency 2. Among heterotrophs, assimilation efficiency: Among heterotrophs EA = A/I A = amount of energy assimilated I = amount of energy ingested Secondary Production: Secondary Assimilation Efficiency For the Uganda elephants: Consumed = 71.5 kcal/m2/year. Lost in urine and feces = 40.2 Assimilation = 31.3 Therefore, assimilation efficiency = Therefore, 31.3/71.5 = 44% 31.3/71.5 Growth or Production Efficiency Efficiency EG = NP/A or EG = 1 – R/A R = respiration rate at this trophic level A = amount of energy assimilated NP = A – R Growth or Production Efficiency Efficiency For the elephant For herd: herd: R = 30.96 A = 31.3 31.3 NP = 0.34 EG = 0.34/31.3 = 1.1% Assimilation Efficiency Assimilation Determined by: Determined 1) 1) 2) 2) 1. type of organism (heterotherm versus type homeotherm) and type of food consumed. Homeotherms (birds and mammals) have, Homeotherms in general, higher assimilation efficiencies than heterotherms (insects and reptiles for example). example). Assimilation Efficiency: Types of Food Types 2. High quality easily assimilated foods: Flesh of vertebrates and arthropods Plant sap, nectar and seeds Assimilation Efficiency: Types of Food Types Spittlebug (heterotherm) eating nectar (high quality food). Assimilation Efficiency: Types of Food Types 3. Low quality poorly Low assimilated foods: assimilated Anything with large Anything amounts of cellulose, lignin and fiber (leaves, wood, bark etc.). etc.). Cellulose Lignin Assimilation Efficiency Assimilation Growth Efficiency Growth Homeotherms use large amounts of energy in respiration, thus have low growth efficiencies. growth Heterotherms have higher growth efficiencies. efficiencies. Growth Efficiency: Growth Heterotherms Heterotherms Grasshoppers Spittlebug Lepidopteran Harvester Ant Spittlebug 36.7% 41.5% 41.8% 0.7% 0.7% California butterfly, Lycaena helloides Growth Efficiency: Growth Homeotherms Homeotherms Meadow Vole Old Field Mouse Meadow Vole Uganda Cob African Elephant Uganda Cob 1.8% 2.9% 1.5% 1.5% Consumption Efficiency Consumption How much of plant NP do herbivores How gather? gather? Answer differs greatly among ecosystems. Four types: Four 1. Forests 1. = low consumption 2. Grasslands = moderate consumption Consumption Efficiency Consumption 3. Aquatic/oceanic = high consumption. Aquatic/oceanic 4. Streams Streams = energy flow dominated by detritus with very little plant NP within the stream ecosystem. stream General Rules for the Proportion of Primary Production Harvested by Grazers as Contrasted with Decomposers (Grazing Food Chain versus Decomposer Food Chain Type of Ecosystem Percent of Primary Production Processed by Grazers/Herbivores Percent of Primary Production Processed by Decomposers Forests 1 – 10 90 – 99 11 – 60 40 – 89 60 – 99 1 - 40 Grasslands Aquatic Ecosystems Efficiencies: Review Efficiencies: 1. Photosynthetic Efficiency: PE = NP/PAR 2. Assimilation Efficiency: EA = A/I A/I Efficiencies: Review Efficiencies: 3. Growth Efficiency: EG = NP/A or EG = 1 – R/A NP = A – R R = respiration rate at this trophic level Sample Problem Sample Farmer John has a fishpond. He Farmer wishes to increase his fish yield. He hires an ecologist who measures net primary production of the pond. The figure is 3200 kcal/m2 of pond surface figure area. Sample Problem Sample If solar radiation (PAR) is measured at If 10,000 kcal/m2/year, what is the 10,000 /year, photosynthetic efficiency of this pond? Sample Problem Sample The ecologist next drains the pond The and finds that it primarily contains one species of herbivorous fish. When tested in an aquarium the ecologist finds that it assimilates 45% of what it eats. eats. Sample Problem Sample If this is correct, and the fish If consumes 2000 kcal/m2/year, what is consumes /year, the expected net production of fish if the R/A ratio is 65%? What is the growth efficiency? growth Sample Problem: Answers Sample Part one. Part Given the equation: Given PE = NP/PAR NP/PAR We have: PE = 3200/10,000 = 32.0% Sample Problem: Answers Sample Part two. First we have: EA = A/I or 0.45 = A/2000 and A=900 or kcal/m2/yr. kcal/m Next we have: NP NP = A - R. But 0.65 = R/A and R = 0.65 A. Sample Problem: Answers Sample Substituting 0.65A for R We have: NP = A - 0.65A = 0.35A NP Since A = 900. We have: NP = (.35)(900) = 315 kcal/m2/yr. Finally: EG = NP/A = 35% EG Questions? ...
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This note was uploaded on 01/23/2012 for the course BIOL/EVPP 307 taught by Professor Crerar during the Summer '11 term at George Mason.

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