Cycling energy

• The Working Ecosystem


  1. Energy Flow

  2. Chemical Cycling
• A community interacts with abiotic factors, forming an ecosystem
• Two main processes in an ecosystem

  • Energy flow
  • Chemical (nutrient) cycling
• Energy flow


  Light energy flows through ecosystems (i.e., from the sun, through plants, animals, and decomposers), and is lost as heat
• Chemical cycling


  Chemicals (i.e., matter/nutrients), are recycled between air, water, soil, and organisms
• Ecosystem ecology emphasizes energy flow and chemical cycling
• Conservation of Energy


  The first law of thermodynamics states that energy cannot be created or destroyed, only transformed
• Conservation of Mass


  The law of conservation of mass states that matter cannot be created or destroyed. Chemical elements are continually recycled within ecosystems
• Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products
• Trophic Levels


  Feeding positions that biotic components occupy on the food chain
• Food Chain


  Stepwise flow of energy and nutrients from plants (producers) to carnivores (secondary and higher-level consumers)
• Food Web


  A branching food chain with complex trophic interactions
• Species may play a role at more than one trophic level
• Food webs can be simplified by grouping species with similar trophic relationships into broad functional groups or isolating a portion of a community that interacts very little with the rest of the community
• Autotrophs (producers)


  Build molecules (e.g., carbohydrates) themselves using photosynthesis or chemosynthesis
• Autotrophs


  • Cyanobacteria
  • Chemosynthetic bacteria
• Heterotrophs (consumers)


  Depend on the biosynthetic output of other organisms. They include herbivores, carnivores, and omnivores
• Detritivores


  Consumers that derive their energy from detritus, nonliving organic matter (waste)
• Detritivores


  • Scavengers (e.g., flies, pill bugs, carrion beetles, nematodes, ravens, vultures, earthworms)
  • Decomposers (e.g., bacteria, fungi)
• Decomposition connects all trophic levels and is essential for the continuation of life on earth
• Trophic Efficiency


  Percentage of production transferred from one trophic level to the next
• Low trophic efficiencies can be represented in a biomass pyramid
• Pyramid of Biomass


  Represents the amount of living organic material in an ecosystem
• Pyramid of Numbers


  Represents the number of organisms at each trophic level
• The energy supply limits the length of food chains