TR

Energy Flow Through Ecosystems

Ecosystems and Energy

  • Ecosystem: the sum of all the organisms living in a given area and the abiotic factors they interact with
    • Biotic factors: living, or once living, components of an environment
    • Abiotic factors: nonliving (physical and chemical properties of the environment)
  • 1st law of thermodynamics: energy can neither be created nor destroyed, only transferred
    • Law of conservation of mass: chemical elements are continually recycled in the environment
  • 2nd law of thermodynamics: exchanges of energy increase the entropy of the universe
  • A net gain in energy results in energy storage or growth of an organism
  • A net loss of energy results in loss of mass and eventual death of an organism
  • Organisms use different strategies to regulate body temperature
    • Endotherms: use thermal energy from metabolism to maintain body temperatures
    • Ectotherms: use external sources (ie sun/shade or other organisms) to regulate their body temperature

Metabolic Rate

  • Metabolic rate: the total amount of energy an animal uses in a unit of time
    • Can be measured in calories, heat loss, or by the amount of oxygen consumed (or CO2 produced)
    • Oxygen is used in cellular respiration and CO2 is produced as a by-product 
    • An animal’s metabolic rate is related to its body mass
    • Smaller organisms = higher metabolic rate
    • Larger organisms = lower metabolic rate

Semelparity vs Iteroparity

  • Semelparity
    • Big-bang reproduction
    • Many offspring produced at once
    • Individual often dies afterwards
    • Less stable environments
  • Iteroparity
    • Repeated reproduction
    • Few, but large offspring
    • More stable environments

Trophic Levels

  • Species can be grouped into trophic levels based upon their mains source of nutrition and energy
  • Unlike mass, energy CANNOT be recycled
    • The sun constantly supplies energy to ecosystems
  • Primary producers (autotrophs): use light energy to synthesize organic compounds
    • Plants, algae, photosynthetic plankton
    • Some organisms are chemosynthetic (vs photosynthetic) meaning they produce food using the energy created by chemical reactions
      • Ie some bacteria and archaea organisms
  • Heterotrophs: rely on autotrophs because they cannot make their own food
    • Primary consumers: herbivores
    • Secondary consumers: carnivores that eat herbivores
    • Tertiary consumers: carnivores that eat other carnivores
    • Decomposers: get energy from detritus (nonliving organic material; leaves, wood, dead organisms)
    • Include fungi and many prokaryotes
    • Important for recycling chemical elements
  • The trophic structures of a community are determined by the feeding relationships between organisms
    • Food chain: the transfer of food energy up the trophic levels
    • Food webs: linked food chains
  • Any changes to the availability of energy can disrupt ecosystems
    • For example:
    • If energy resources change, so can the number and size of trophic levels (Increase energy, increase trophic levels/size; decrease energy, decrease trophic levels/size)
    • A change at the producer level can affect the number and size of the remaining trophic levels

Primary Production

  • Primary production: the amount of light energy that is converted to chemical energy
    • Primary producers set a “spending limit” for the entire ecosystems energy budget
    • Gross primary production (GPP): total primary production in an ecosystem
    • Net primary production (NPP): the GPP minus the energy used by the primary producers for respiration (Ra)
  • Satellite images show that different ecosystems have varying NPP

Secondary Production

  • Secondary production: the amount of chemical energy in a consumer’s food that is converted to new biomass
    • The transfer of energy between trophic levels is at around 10% efficiency

Pyramid of Biomass

  • Biomass: the total weight of dry matter (dry weight) present in the ecosystem at any one time; the total mass of organisms at a trophic level.
  • With less energy at higher trophic levels, there are usually fewer organisms as well.
  • Organisms tend to be larger in size at higher trophic levels, but their smaller numbers result in less biomass.

Matter Cycling

  • Unlike energy, matter cycles through ecosystems
    • Matter is found in limited amounts, unlike solar energy
    • Biogeochemical cycles: nutrient cycles that contain both biotic and abiotic factors
    • Water, carbon, nitrogen, and phosphorus cycle

Water Cycle

  • Biological importance of the water cycle: water is essential for all life and influences the rate of ecosystem processes

Carbon Cycle

  • Biological importance of the carbon cycle: carbon is essential for life and required in the formation of organic compounds

Nitrogen Cycle

  • Biological importance of the nitrogen cycle: nitrogen is important for the formation of amino acids, proteins, and nucleic acids

Phosphorous Cycle

  • Biological importance of the phosphorous cycle: phosphorus is important for the formation of nucleic acids, phospholipids, and ATP (energy)