ecosystems

• Carbon cycle

  • Plants fix carbon dioxide into carbohydrates through photosynthesis
  • Animals ingest and digest plant material
  • Organisms respire, releasing carbon dioxide
  • Decomposers break down dead matter, releasing carbon dioxide
• Ecological succession

  1. Pioneer species colonize bare area

  2. Abiotic factors become less harsh

  3. New species out-compete previous ones

  4. Biodiversity and ecosystem stability increase

  5. Climax community forms
• Deflected succession

  Human activities prevent progress of succession to climax community
• Sampling

  Provides accurate, representative estimate of population size using multiple random samples
• Factors affecting population size

  • Abiotic factors (temperature, oxygen, carbon dioxide, etc.)
  • Interspecific competition
  • Intraspecific competition
  • Predation
• Predator-prey relationship

  • Prey population changes before predator population
  • More prey than predators to sustain the predator population
• Conservation

  Human actions and management to maintain biodiversity and sustainable use of natural resources
• Preservation

  Protecting an area by banning visitors
• Reasons for conservation

  • Ethical (right to life for all organisms, future generations)
  • Social (outdoor enjoyment, health benefits)
  • Economic (medicines, food, timber, tourism)
• Sustainable management

  • Coppicing and pollarding of trees
  • Limiting fishing quotas and sizes
  • Protecting habitats of disease vectors
• Trophic levels


  Stages in the food chain
• Biomass transfer through an ecosystem

  1. Producers

  2. Primary consumers

  3. Secondary consumers

  4. Tertiary consumers
• Producers

  Plants that produce food through photosynthesis
• Primary consumers


  Herbivores that eat the producers
• Secondary consumers


  Organisms that eat the primary consumers
• Tertiary consumers


  Organisms that eat the secondary consumers
• The food chain can be represented by a pyramid with the most producers at the bottom and fewer organisms at each higher trophic level
• Biomass


  Mass of living material in an area or in particular organisms without their water content
• Water content is not included in biomass as it can fluctuate and does not represent the true energy content
• Measuring biomass


  1. Collect sample

  2. Kill organism

  3. Dry in oven at 80°C until mass is constant
• Calorimeter


  Machine that measures the energy content (calories) of an organism
• Units for biomass

  Grams per meter squared for land animals, grams per meter cubed for marine animals
• Biomass is related to the energy content of an organism
• Biomass

  The amount of energy that an organism contains
• Ecological efficiency


  The efficiency in which biomass or energy is transferred from one trophic level to the next
• Ecological efficiency is often considered in percentage terms
• Energy/biomass transfer in a food chain

  1. Producers get eaten by primary consumers

  2. Primary consumers get eaten by secondary consumers

  3. Secondary consumers get eaten by tertiary consumers
• The energy or mass of the producers that actually gets eaten and used as useful energy by the primary consumer is never 100%, usually around 10-20%
• Energy is lost

  When not all of the biomass from one trophic level is consumed by the next
• Reasons for energy loss


  • Not all light energy is used in photosynthesis
  • Other factors affecting photosynthesis rate (e.g. water availability)
  • Energy used up within photosynthesis reactions
  • Respiration by consumers to release energy
  • Excretion of undigested food
• Some parts of food consumed by higher trophic levels cannot be eaten (e.g. bones)
• Useful energy

  Energy used to build body/biomass
• Methods to reduce energy loss/maximise ecological efficiency

  1. Ensure optimal conditions for photosynthesis (temperature, pH, water, CO2)

  2. Keep farm animals indoors to reduce respiration

  3. Provide high energy content feed to animals

  4. Vaccinate animals to prevent illness

  5. Limit animal movement

  6. Genetic engineering/selective breeding of hardy animals
• Decomposers


  Organisms that feed on dead organic matter and turn them into inorganic substances
• Decomposers

  • They secrete enzymes outside their body to digest the food
  • They do external digestion rather than internal digestion
• Detritivores

  Organisms that feed on dead organic matter
• Detritivores

  • They do internal digestion
  • They increase the surface area of the food by munching on it first
• Detritivores increase surface area

  This speeds up the process of decomposition by decomposers
• Carbon cycle

  1. Producers take in CO2 for photosynthesis

  2. Consumers release CO2 through respiration

  3. Decomposers release CO2 by digesting organic matter

  4. Fossil fuels are formed from undecomposed organic matter

  5. Burning fossil fuels releases CO2 back into the atmosphere
• All organic matter contains carbon