Energy ecosystem


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Energy ecosystem

  1. 1. Energy flow in ecosystemsLecture 6 Chap. 6 1
  2. 2. What is an ecosystem?System = regularly interacting and interdependent components forming a unified wholeEcosystem = an ecological system; = a community and its physical environment treated together as a functional system 2
  3. 3. OR, MORE SIMPLYan ecosystem is composed of the organisms and physical environment of a specified area.SIZE: micro to MACRO 3
  4. 4. THE RULES OF ECOLOGYF. A. BAZZAZ:1. Everything is connected to everything else.2. Everything must go somewhere.3. There is no such thing as a free lunch. 4
  5. 5. H. T. Odum:To understand any system you must understand the next larger system. 5
  6. 6. Attributes of EcosystemsOrderDevelopmentMetabolism (energy flow)Material cyclesResponse to the environmentPorous boundariesEmphasis on function, not species 6
  7. 7. ENERGY FLOW IN ECOSYSTEMSAll organisms require energy, for growth, maintenance, reproduction, locomotion, etc.Hence, for all organisms there must be: A source of energy A loss of usable energy 7
  8. 8. Types of energyheat energymechanical energy (+gravitational energy, etc.)chemical energy = energy stored in molecular bonds 8
  9. 9. Transformations of energyHow is solar energy converted to chemical energy?How does this process influence life as we see it on earth?The transformations of energy from solar radiation to chemical energy and mechanical energy and finally back to heat are a traditional topic of Ecosystem Ecology. 9
  10. 10. An ecosystem has abiotic and bioticcomponents:ABIOTIC components:Solar energy provides practically all the energy for ecosystems.Inorganic substances, e.g., sulfur, boron, tend to cycle through ecosystems.Organic compounds, such as proteins, carbohydrates, lipids, and other complex molecules, form a link between biotic and abiotic components of the system. 10
  11. 11. BIOTIC components:The biotic components of an ecosystem can be classified according to their mode of energy acquisition.In this type of classification, there are: Autotrophs and Heterotrophs 11
  12. 12. AutotrophsAutotrophs (=self-nourishing) are called primary producers.Photoautotrophs fix energy from the sun and store it in complex organic compounds(= green plants, algae, some bacteria) lightsimple complexinorganic photoautotrophs organiccompounds compounds 12
  13. 13. Chemoautotrophs (chemosynthesizers) are bacteriathat oxidize reduced inorganic substances(typically sulfur and ammonia compounds)and produce complex organic compounds. oxygenreduced complexinorganic chemoautotrophs organiccompounds compounds 13
  14. 14. Chemosynthesis near hydrothermal vents 14
  15. 15. Other chemoautotrophs:Nitrifying bacteria in the soil under our feet! 15
  16. 16. Heterotrophs Heterotrophs (=other-nourishing) cannot produce their own food directly from sunlight+ inorganic compounds. They require energy previously stored in complex molecules. heatcomplex simpleorganic heterotrophs inorganiccompounds compounds (this may include several steps, with several different types of organisms) 16
  17. 17. Heterotrophs can be grouped as: consumers decomposers 17
  18. 18. Consumers feed on organisms or particulate organic matter.Decomposers utilize complex compounds in dead protoplasm.Bacteria and fungi are the main groups of decomposers.Bacteria are the main feeders on animal material.Fungi feed primarily on plants, although bacteria also are important in some plant decomposition processes. 18
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  20. 20. The Laws of ThermodynamicsEnergy flow is a one-directional process.sun---> heat (longer wavelengths)FIRST LAW of THERMODYNAMICS:Energy can be converted from one form to another, but cannot be created or destroyed. 20
  21. 21. SECOND LAW of THERMODYNAMICSTransformations of energy always result in some loss or dissipation of energyorIn energy exchanges in a closed system, the potential energy of the final state will be less than that of the initial stateorEntropy tends to increase (entropy = amount of unavailable energy in a system)orSystems will tend to go from ordered states to disordered states (to maintain order, energy must be added to the system, to compensate for the loss of energy) 21
  22. 22. ExamplesInternal combustion engines in cars are 25% efficient in converting chemical energy to kinetic energy; the rest is not used or is lost as heat.My house, particularly my girls rooms, goes from a complex, ordered state to a simpler, disordered state. 22
  23. 23. Energy flowSimplistically: heat Producers Consumers Decomposers heatThis pattern of energy flow among different organisms is the TROPHIC STRUCTURE of an ecosystem. 23
  24. 24. It is useful to distinguish different types of organisms within these major groups, particularly within the consumer group. Consumers 24
  25. 25. Terminology of trophic levelsWe can further separate the TROPHIC LEVELS, particularly the Consumers:Producers (Plants, algae, cyanobacteria; some chemotrophs)--capture energy, produce complex organic compoundsPrimary consumers--feed on producersSecondary consumers--feed on primary consumersTertiary consumers--feed on secondary consumers 25
  26. 26. More trophic levels:Detritivores--invertebrates that feed on organic wastes and dead organisms (detritus) from all trophic levelsDecomposers--bacteria and fungi that break down dead material into inorganic materials 26
  27. 27. Alternate TerminologyProducers = plants etc. that capture energy from the sunHerbivores = plant-eatersCarnivores = animal-eatersOmnivores--eat both animals and plantsSpecialized herbivores:Granivores--seed-eatersFrugivores--fruit-eaters 27
  28. 28. Together, these groups make up a FOOD CHAINE.g., grass, rabbit, eagle Carnivore Herbivore Producer 28
  29. 29. CarnivoresCarnivores can be further divided into groups:quaternary carnivore (top)tertiary carnivoresecondary carnivoreprimary carnivoreThe last carnivore in a chain, which is not usually eaten by any other carnivore, is often referred to as the top carnivore. 29
  30. 30. Foodchains 30
  31. 31. ProblemsToo simplisticNo detritivoresChains too long 31
  32. 32. Rarely are things as simple as grass, rabbit, hawk, or indeed any simple linear sequence of organisms.More typically, there are multiple interactions, so that we end up with a FOOD WEB. 32
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  34. 34. Energy transfers among trophiclevelsHow much energy is passed from one trophic level to the next?How efficient are such transfers? 34
  35. 35. Biomass--the dry mass of organic material in the organism(s).(the mass of water is not usually included, since water content is variable and contains no usable energy)Standing crop--the amount of biomass present at any point in time. 35
  36. 36. Primary productivityPrimary productivity is the rate of energy capture by producers.= the amount of new biomass of producers, per unit time and space 36
  37. 37. Gross primary production (GPP) = total amount of energy capturedNet primary production (NPP) = GPP - respirationNet primary production is thus the amount of energy stored by the producers and potentially available to consumers and decomposers. 37
  38. 38. Secondary productivity is the rate of production of new biomass by consumers, i.e., the rate at which consumers convert organic material into new biomass of consumers.Note that secondary production simply involves the repackaging of energy previously captured by producers--no additional energy is introduced into the food chain.And, since there are multiple levels of consumers and no new energy is being captured and introduced into the system, the modifiers gross and net are not very appropriate and are not usually used. 38
  39. 39. Ecological pyramidsThe standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain. carnivores herbivores producersNote that the complexities of the interactions in a food web are not shown in a pyramid; but, pyramids are often useful conceptual devices--they give one a sense of the overall form of the trophic structure of an ecosystem. 39
  40. 40. Pyramid of energyA pyramid of energy depicts the energy flow, or productivity, of each trophic level.Due to the Laws of Thermodynamics, each higher level must be smaller than lower levels, due to loss of some energy as heat (via respiration) within each level. Energy flow in : carnivores herbivores producers 40
  41. 41. Pyramid of numbersA pyramid of numbers indicates the number of individuals in each trophic level.Since the size of individuals may vary widely and may not indicate the productivity of that individual, pyramids of numbers say little or nothing about the amount of energy moving through the ecosystem. # of carnivores # of herbivores # of producers 41
  42. 42. Pyramid of standing cropA pyramid of standing crop indicates how much biomass is present in each trophic level at any one time.As for pyramids of numbers, a pyramid of standing crop may not well reflect the flow of energy through the system, due to different sizes and growth rates of organisms. biomass of carnivores biomass of herbivores biomass of producers (at one point in time) 42
  43. 43. Inverted pyramidsA pyramid of standing crop (or of numbers) may be inverted, i.e., a higher trophic level may have a larger standing crop than a lower trophic level.This can occur if the lower trophic level has a high rate of turnover of small individuals (and high rate of productivity), such that the First and Second Laws of Thermodynamics are not violated. biomass of carnivores biomass of herbivores biomass of producers (at one point in time) 43
  44. 44. Pyramid of yearly biomassproductionIf the biomass produced by a trophic level is summed over a year (or the appropriate complete cycle period), then the pyramid of total biomass produced must resemble the pyramid of energy flow, since biomass can be equated to energy. Yearly biomass production (or energy flow) of: carnivores herbivores producers 44
  45. 45. Note that pyramids of energy and yearly biomass production can never be inverted, since this would violate the laws of thermodynamics.Pyramids of standing crop and numbers can be inverted, since the amount of organisms at any one time does not indicate the amount of energy flowing through the system.E.g., consider the amount of food you eat in a year compared to the amount on hand in your pantry. 45
  46. 46. Examples of food websthe North Seaa hypothetical web--effects on species diversity 46
  47. 47. 7-12 mm 13-40 mm 40-130 mm AdultHerringin theNorth Sea 47
  48. 48. a hypothetical web--effects on species diversity 48
  49. 49. Examples of pyramidsTerrestrial and fresh-water communitiesOcean communities--English Channel 49
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