Energy and chemical cycling

• Levels of life in ecology

  • Organism
  • Population
  • Community
  • Ecosystem
• Community


  All the organisms that live together in a particular place
• Habitat


  The place where a community lives, including biotic and abiotic factors
• Ecosystem


  An ecological system that is largely self-sustaining, consisting of a collection of organisms and their physical environment
• Most ecosystems obtain their energy from the sun, but there are exceptions
• Communities around deep sea vents cannot rely on sun energy
• The biodiversity of deep sea vents is 4 to 5 orders of magnitude higher than the surrounding seafloor
• How deep sea vent communities obtain energy

  1. Water spewing from vents contains high concentrations of sulfur compounds

  2. Chemoautotrophic bacteria harness the energy within these compounds and environmental CO2 to produce glucose, without the energy of the sun
• Food web in deep sea vent communities

  • Chemoautotrophic bacteria make glucose from energy in sulfur compounds and CO2
  • Small crustaceans feed on the bacteria
  • The top predators are fishes
• Tube worms in deep sea vents

  • Have a symbiotic relationship with bacteria
  • The worms have no mouth or digestive tract, the red tip is a respiratory surface that acquires oxygen and sulfur compounds
  • Bacteria living in a specialized organ in the worm's body get energy from the sulfur and share it with the worm
  • Amongst the fastest growing invertebrates known, can grow more than 2 meters long
• Bacteria do harness chemical energy to sustain their communities
• We will now concentrate on the vast majority of ecosystems that are based on light energy from the sun - solar radiation
• Producers


  The organisms that first capture the energy, plants and algae which produce their own energy-storing molecules by carrying out photosynthesis
• Consumers


  All other organisms in an ecosystem that obtain their energy-storing molecules by consuming plants or other animals
• Other examples of consumers

  • Red panda - consumer, food is bamboo
• Trophic level


  The feeding level composed of those organisms within an ecosystem who are the same number of consumption "steps" away from the sun
• In most ecosystems, the path of energy is not a simple linear one because individual animals often feed at several trophic levels, creating a complicated path of energy flow called a food web
• Trophic levels in a food web

  • Primary Producers
  • Primary Consumers (Herbivores)
  • Secondary Consumers (Carnivores)
  • Omnivores
  • Tertiary Consumers
  • Quaternary Consumers (Top Carnivores)
  • Detritivores & Decomposers
• There is a limit to the number of trophic levels
• Primary Productivity


  The total amount of light energy converted to organic compounds in a given area per unit of time
• Net Primary Productivity


  The total amount of energy fixed by photosynthesis per unit of time, minus the energy expended by the metabolic activities of the ecosystem
• There is not even close to 100% conversion of energy in an ecosystem
• Biomass


  The total weight of all ecosystem organisms, which increases as a result of the ecosystem's net productivity
• Energy loss in ecosystems

  1. When a plant uses energy from sunlight to make structural molecules like cellulose, it loses a lot of the energy as heat, only about half the captured energy ends up stored in its molecules

  2. The amount of energy that ends up in the herbivore's body (growth) is approximately an order of magnitude less than the energy present in the plant molecules it eats, with only 5-20% used for growth

  3. Half the energy is passed as feces, and of the half that is absorbed, two-thirds is used as fuel for cellular respiration

  4. Similarly, when a carnivore eats the herbivore, an order of magnitude is lost from the amount of energy present in the herbivore's molecules
• Most food chains are short, only 3 or 4 steps, so very little usable energy remains in the system after it has been incorporated into the bodies of organisms at 4 consecutive trophic levels
• The loss of energy that occurs at each trophic level places a limit on how many top-level carnivores a community can support
• Only about 1/1000th of the energy captured by photosynthesis passes all the way through a 3-stage food chain to a tertiary consumer
• This explains why there are no predators that subsist on, for example, lions or eagles, as the biomass of these animals is simply insufficient to support another trophic level
• Top level predators tend to be fairly large animals, as the small residual biomass available at the top of the pyramid is concentrated in a relatively small number of individuals
• Pyramids of production


  Graphical representations where the width of each tier indicates how much of the chemical energy of the tier below is incorporated into organic matter of that trophic level, can represent number of individuals or total biomass
• Humans as omnivores


  Humans eat both plant material and meat, acting as primary, secondary, tertiary, and quaternary consumers depending on their diet
• Energy flow


  Energy flows through the earth's ecosystems in one direction
• Material cycling


  The physical components of ecosystems are passed around or reused within ecosystems
• Cycling


  The constant re-use of material within ecosystems
• Supply of chemical elements (nutrients) to an ecosystem is limited
• Chemical cycling


  1. Chemical elements are cycled between abiotic and biotic components

  2. Plants build organic molecules from chemical elements in inorganic form

  3. Consumers acquire organic molecules from plants or other consumers

  4. Decomposers return elements to inorganic form
• Life depends on the recycling of chemicals
• No new influx of chemical elements (except occasional meteorite)
• Chemical cycling


  1. Chemical elements cycle as organisms acquire nutrients, incorporate into tissues, release waste products, then die

  2. Decomposers replenish pool of inorganic nutrients to build new organic matter
• Abiotic reservoirs


  • Atmosphere (gases cycle globally)
  • Inorganic forms of chemicals in soil and rocks (soil is main reservoir for nutrients in a local cycle)