B7: Ecology

• Ecology


  The study of the relationships between living organisms and their environment
• Key terms in ecology

  • Habitat - the place where an organism lives
  • Community - all the populations of different species living in a habitat
  • Competition - the interactions between different species living in a habitat
  • Abiotic factors - non-living components of the environment, e.g. temperature
  • Biotic factors - living components of the environment, e.g. food
• Organisms compete for resources to survive
• Plants need light, air, water and mineral ions (nutrients) from the soil
• Organisms compete with other species (and members of their own species) for the same resources
• In a community, each species depends on other species for things such as food, shelter, pollination and seed dispersal
• The interdependence of all the living things in an ecosystem means that any major change in the ecosystem (such as one species being removed) can have far-reaching effects
• Stonefly larvae are particularly sensitive to pollution
• If pollution killed stonefly larvae in a stream

  It would have effects on other organisms in the food web, such as water spiders, sticklebacks, etc.
• Stable communities include tropical rainforests and ancient oak woodlands
• Abiotic factors

  Non-living components of the environment, e.g. temperature, light, moisture, carbon dioxide level
• Biotic factors


  Living components of the environment, e.g. new predators, competition, new pathogens, availability of food
• A change in an abiotic factor

  Can affect the size of populations in a community
• A change in a biotic factor

  Can also affect the size of populations in a community
• Adaptations allow organisms to survive in different environments
• Types of adaptations

  • Structural - changes to the physical features of an organism
  • Behavioural - changes to the way an organism behaves
  • Functional - changes to the internal processes of an organism
• Some microorganisms (e.g. bacteria) are known as extremophiles and are adapted to live in very extreme conditions
• Food chain

  A series of organisms where each one feeds on the one below it
• Producers make their own food using energy from the sun
• Consumers that hunt and kill other animals are called predators, and their prey are what they eat
• The population of prey

  Increases, then the population of predators increases, then the population of prey decreases, and this cycle continues
• Predator-prey cycles are always out of phase with each other
• Quadrat


  A square frame used to study the distribution of small organisms
• Using quadrats to study distribution

  1. Place quadrat at random point

  2. Count organisms within quadrat

  3. Repeat in multiple locations

  4. Calculate mean number of organisms per quadrat

  5. Compare means between different areas
• Population size


  Also called abundance, the total number of a particular organism in a given area
• Estimating population size using quadrats

  1. Calculate mean number of organisms per m²

  2. Multiply mean by total area of habitat
• Transect

  A line along which observations are made to study the distribution of organisms
• The two mene. E.g. you might find 2 daisies per m in the shede, and 22 daisies per m2 (lots more) in the open field.
• Estimating the population size of an organism in one area

  1. Work out the mean number of organisms per m²

  2. Multiply the mean by the total area of the habitat
• Population size


  Also called abundance
• Using transects to study the distribution of organisms along a line

  1. Mark out the area you want to study using a tape measure

  2. Collect data along the line by counting all the organisms that touch the line

  3. Or collect data using quadrats placed next to each other along the line or at intervals
• Estimating the percentage cover of a quadrat

  1. Count the number of squares covered by each organism

  2. Make this into a percentage by dividing the number of squares covered by the organism by the total number of squares in the quadrat (100), then multiply the result by 100
• Environmental changes can affect the distribution of organisms
• Environmental changes that can affect organisms

  • Changes in the availability of water
  • Changes in temperature
  • Changes in the composition of atmospheric gases
• The rise in average temperature is due to global warming, which has been caused by human activity
• The water cycle

  1. Energy from the Sun makes water evaporate from the land and sea, forming water vapour

  2. The warm water vapour is carried upwards and cools, condensing to form clouds

  3. Water falls from the clouds as precipitation onto land, where it provides fresh water for plants and animals

  4. The water then drains into the sea, before the whole process starts again
• The carbon cycle

  1. CO₂ is removed from the atmosphere by green plants and algae during photosynthesis

  2. When the plants and algae respire, some carbon is returned to the atmosphere as CO₂

  3. When the plants and algae are eaten by animals, some carbon becomes part of the fats and proteins in their bodies

  4. When the animals respire, some carbon is returned to the atmosphere as CO₂

  5. When plants, algae and animals die, detritus feeders and microorganisms feed on their remains, returning CO₂ to the atmosphere

  6. Animals also produce waste that is broken down, returning CO₂ to the atmosphere

  7. The combustion of wood and fossil fuels also releases CO₂ back into the air
• Decay

  The process where microorganisms and detritus feeders break down plant and animal material and waste
• Factors affecting the rate of decay

  • Temperature
  • Oxygen availability
  • Water availability
  • Number of decay organisms
• Biogas

  Mainly made up of methane, which can be burned as a fuel. Produced by the anaerobic decay of plant and animal waste.