Ecology

• Transfer of Energy


  The process by which energy is passed from one organism to another in an ecosystem
• The Sun


  • Principal source of energy input to biological systems
  • All energy transfers on Earth can be traced back to the Sun
• Photosynthesis


  Process that converts solar energy into chemical energy
• All life depends, directly or indirectly, on photosynthesis
• Flow of Energy from the Sun to Earth

  1. Around half of the Sun's energy that enters the atmosphere reaches the surface

  2. Some of this energy powers photosynthesis which all life depends upon
• Energy flow


  Energy flows through living organisms, including light energy from the Sun and chemical energy in organisms<|>Energy is eventually transferred to the environment eg. as heat
• Food Chain Definitions

  • Producer - An organism that can produce its own food, using sunlight or other energy sources
  • Herbivore - An animal that eats only plants
  • Carnivore - An animal that eats other animals
  • Primary consumer - An herbivore that eats producers
  • Secondary consumer - A carnivore that eats primary consumers
  • Tertiary consumer - A carnivore that eats secondary consumers
  • Decomposer - An organism that feeds on dead or decaying matter by breaking it down
• Food Chain


  1. Shows the transfer of energy from one organism to the next, starting with a producer

  2. The source of all energy in a food chain is light energy from the Sun

  3. Energy is transferred from one organism to another by ingestion (eating)
• Food Web


  A network of interconnected food chains<|>More realistic way of showing connections between organisms within an ecosystem as animals rarely exist on just one type of food source
• If the population of earthworms decreases

  • The population of grass plants would increase
  • The populations of frogs and mice would decrease significantly
  • The population of sparrows would decrease slightly
• Most of the changes in populations of animals and plants happen as a result of human impact - either by overharvesting of food species or by the introduction of foreign species to a habitat
• Due to interdependence, changes can have long-lasting knock-on effects to organisms throughout a food chain or web
• Trophic Levels


  • Producers - They produce their organic nutrients usually using energy from the Sun
  • Primary consumers - Herbivores - they feed on producers (plants)
  • Secondary consumers - Predators that feed on primary consumers
  • Tertiary consumers - Predators that feed on secondary consumers
  • Quaternary consumers - Predators that feed on tertiary consumers
• Transfer of Energy


  1. Energy has to be consumed (eaten) to be passed on

  2. Not all of the energy an organism receives gets passed on - some is lost through waste products, movement, heat, and undigested waste
• The inefficient loss of energy at each trophic level explains why food chains are rarely more than 5 organisms long
• It is more energy efficient for human consumers to eat crop plants than to eat livestock that have been fed on crop plants
• Pyramid of Numbers


  1. Shows how many organisms we are talking about at each level of a food chain

  2. The width of the box indicates the number of organisms at that trophic level
• Pyramids of numbers are not always pyramid-shaped
• Pyramid of Energy


  Shows how much energy is passed on at each trophic level
• Pyramid of Biomass


  1. Shows how much mass the creatures at each level would have without including all the water that is in the organisms (their 'dry mass')

  2. Pyramids of biomass are ALWAYS pyramid-shaped
• The Carbon Cycle


  1. Carbon is taken out of the atmosphere by photosynthesis

  2. It is passed on to animals and decomposers by feeding

  3. It is returned to the atmosphere by respiration, and by the combustion of fossil fuels

  4. Deforestation is reducing the number of producers that can take carbon dioxide out of the atmosphere
• The Nitrogen Cycle


  1. Nitrogen-fixing bacteria convert N2 gas into nitrates in the soil

  2. Lightning can also 'fix' N2 gas

  3. Plants absorb nitrates and use the nitrogen to make proteins

  4. Animals get nitrogen from the proteins in plants and animals they eat

  5. Waste and decomposition return nitrogen to the soil as ammonium compounds

  6. Nitrifying bacteria convert ammonium to nitrites and then nitrates, which plants can absorb

  7. Denitrifying bacteria convert nitrates back to N2 gas
• Nitrogen fixation


  Bacteria found 'free-living' in soil and in root nodules of leguminous plants take N2 gas and change it into nitrates in the soil
• Nitrogen fixation by lightning

  Lightning can 'fix' N2 gas, splitting the bond between the two atoms and turning them into nitrous oxides like N2O and NO2 that dissolve in rainwater and 'leach' into the soil
• Nitrogen absorption by plants

  Plants absorb the nitrates they find in the soil and use the nitrogen in them to make proteins
• Nitrogen transfer to animals

  Animals eat the plants (or other animals) and get the nitrogen they need from the proteins in the plant or animal
• Nitrogen return to soil

  Waste (urine and faeces) from animals sends nitrogen back into the soil as ammonium compounds (the urea in urine contains nitrogen)
• Nitrogen decomposition


  When the animals and plants die, they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers
• Nitrification


  Ammonium compounds are converted to nitrites and then to nitrates by nitrifying bacteria, which can then be absorbed by plants
• Denitrification


  Denitrifying bacteria take the nitrates out of the soil and convert them back into N2 gas
• Farmers can help

  Reduce the amount of denitrifying bacteria by ploughing and turning over soil
• The Nitrogen Cycle
• Population


  A group of organisms of the same species living in the same place at the same time
• Community


  Includes all of the populations living in the same area at the same time
• Community


  • Each species depends on other species for food, shelter, pollination, seed dispersal etc
  • If one species is removed it can affect the whole community
• Habitat


  The place where an organism lives
• Ecosystem


  All the biotic factors and all the abiotic factors that interact within an area at one time
• Biotic factors


  • All the living components such as plants and animals
• Abiotic factors


  • All the non-living components such as light intensity, mineral ions, water availability
• Ecosystems can vary greatly in size and scale