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)