6.3.1 Ecosystems

• What is an ecosystem?

  All living (biotic) organisms and non-living (abiotic) components and their interactions
• What is a population?

  The number of individuals of the same species living in the same place at the same time
• What is a community?

  All the organisms of all the different species living in a habitat
• What is a niche?


  The role of an organism in the ecosystem
• Abiotic factors

  • temperature
  • light intensity
  • oxygen concentration
  • carbon dioxide concentration
  • water supply
  • pH
  • availability of inorganic ions
  • edaphic features
  • atmospheric humidity
  • wind speed
• Biotic factors

  • feeding of herbivores on plants
  • predation
  • parasitism
  • mutualism
  • competition
• What is net primary production?

  • energy available at each tropic level
  • measures in kilojoules per metre squared per year (Kj m^-2 yr^-1)
  • as biomass is transferred, so is the energy contained
  • ecological efficiency, decreases by a factor of 10 each time
  • increased by high temperatures, increase in sunlight as more photosynthesis occurs so more storage of biomass
• What is net primary objective units?

  Kj m ^-2 y ^ -1
• What factors can increase the net primary production?

  High temperature and increase in sunlight> more photosynthesis> more storage of biomass
• Producers only convert 1-3% of sunlight into chemical energy. Why?

  • not all light hits the chlorophyll
  • not all light hitting leaves is absorbed, can be transmitted through, reflected or of the wrong wave length
• what is productivity?

  the rate at which the plant converts light energy into chemical potential energy
• what is gross primary productivity?

  the total quantity of energy converted by plants in productivity
• what is net primary production?

  energy which remains as chemical energy after the plants have supplied their own needs in respiration
• Consumers at each trophic level convert at most 10% of biomass in their food to their own organic tissue. They do this because;

  • not all biomass is eaten (e.g. bones/ roots)
  • some lost as heat to the environment through respiration
  • some excreted (urine and faeces)
  • some biomass from the previous trophic level cant be digested (e.g. cellulose)
• How to measure ecological efficiency

  energy or biomass available after the transfer/ energy or biomass available before x 100
• How can human activities manipulate the transfer of energy?

  • indoors; less energy lost through heat, crowded so not moving as much and using energy for metabolic processes
  • high protein diet; increased muscle mass
  • vaccination; prevents energy lost through immune response, more for biomass
  • slaughter before maturity
  • genetically modified
• What examples of nitrogen fixing through bacteria are there?

  • rhizobium (mutualistic in root nodules)
  • azatobacter (free living)

  converted into ammonia (NH3)
• Equipment used to measure species richness and evenness

  • frame quadrant, pooter, point quadrant, sweep net
• What is a pioneer community?

  the first community to appear in a bare area, first stage of primary succession;

  • produce large numbers of wind-carried seeds or spores
  • biomass is low
  • many species are liches and mosses
• What are ecosystems?

  • affected by biotic and abiotic factors
  • dynamic
  • flow of biomass between tropic levels
• What bacteria converts ammonium compounds to nitrates?

  nitrosomonas
• What process usually occurs under anaerobic conditions?

  nitrogen fixation
• Benefits of maintaining ecosystems

  • ecotourism
  • education and increased awareness
  • scientific study
• Why are ecosystems described as dynamic?

  there’s changes over time
• What is the name of the animal and plant populations present following primary succession?

  Climax community, they are stable
• What happens to nitrogenous compounds so plants can take them up and use them?

  nitrogenous compound converted to nitrite via Nitrosomonas the converted to nitrate via Nitrobacter