Ecosystems

• Ecosystems - all the organisms living in a community, abiotic and biotic
• 2 main ecosystem processes:

  • energy flow
  • chemical cycling

  energy flows through ecosystems while matter cycles within them

  • in as light —(used energy)—> out as heat
• conservation of energy:

  first law of thermodynamics - energy cannot be created or destroyed, only transformed

  • energy enters as solar radiation, is conserved, and ”lost” as heat

  second law of thermodynamics - every exchange of energy increases the entropy of the universe

  • inefficient energy transfer: energy is always lost as heat
• conservation of mass:

  law of conservation of mass - matter cannot be created or destroyed
• primary production - amount of light energy converted to chemical energy by autotrophs

  • gross primary production - total primary production
  • net primary production - total energy after producers use it, available to consumers: GPP minus energy used by primary production for respiration
  • NPP varies between ecosystems

  equatorial is most productive
• Primary production in aquatic ecosystems:

  • light limitation - depth of light penetration affects primary production in the photic zone
  • nutrient limitation - nutrients limit primary production in the benthic zone
  • limiting nutrient - element that must be added for production to increase in an area: nitrogen and phosphorous
• primary production in terrestrial ecosystems:

  • temperature and moisture affect primary production in a large scale
• secondary production - amount of chemical energy in food converted to new biomass
• Production efficiency:

  • tropic efficiency - percentage of production transferred: how much energy gets passes from one ink of the food chain to the next
  • 10% of energy is passed on
• green world hypothesis - more # of producers than #’ higher up the food chain

  factors that keep herbivores in check: more plants left behind

  • plant defenses - not all get eaten
  • limited availability of essential nutrients in plants for herbivores - no nutrient, herbivores don’t get eaten
  • abiotic factors favor against herbivores - plants don’t migrate
  • intraspecific competition between herbivores - competition within a species
  • interspecific interactions between herbivores - competition between species
• Biogeochemical cycle - how nutrients have biotic and abiotic component in cycle

  Water cycle:

  • living factors - oceans, glaciers, lakes, rivers, groundwater
  • non-living factors - atmosphere: evaporation (up), precipitation (down)

  Carbon cycle:

  • carbon reservoirs in fossil fuels, soils, and sediment
  • transfer from plants/animals to the atmosphere
  • in through photosynthesis — out through respiration

  Nitrogen cycle:

  • nitrogen reservoir in atmosphere
  • bacteria convert to NH4+ and NO3- for plant

  Phosphorous cycle:

  • PO4 3- —(sedimentation)—sedimentary rock—(erosion)—> organisms
• Human activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems
• Agriculture and Nitrogen Cycling:

  • agriculture removes nutrients from the ecosystem, mainly nitrogen
  • industrial produced fertilizer is the main method to replenish lost nitrogen
• Contamination of Aquatic Environments:

  • critical load - plants can only take up so mcuh
  • eutrophication - fertilizer flows into water source, producers go out of control
  • dead zone - so much eutrophication
• Toxins in the Environment:

  • biological magnification - concentrates toxins at higher trophic levels, where biomass is lower
  • PCBs and DDT are subject to biological magnification
• Greenhouse Gases and Global Warming:

  • steadily increasing levels of atmospheric carbon dioxide - due burning fossil fuels
  • FACTS-I experiment - CO2 influence on tree growth
• Depletion of Atmospheric Ozone:

  • thining
  • ozone depletion causes DNA damage in plants and poorer phytoplankton growth
  • stopped producing CFCs so ozone depletion leveled out
• density-independent: birth rate and death rate do not change with population density