B7 ecology

• Ecosystem


  Community of organisms that interact with their environment
• Ecosystems


  • Affected by biotic factors like food availability and competition
  • Affected by abiotic factors like light intensity, temperature and amount of water
• Changes to a population in a community

  Can have knock-on effects on the other species
• Interdependence


  Species rely on each other to survive
• Extremophiles


  Bacteria adapted to live in extreme conditions
• Key terms


  • Individuals of the same species can breed together to produce fertile offspring
  • Organisms live in habitats
  • All the individuals from one species living in a habitat is called a population
  • Populations of different species that all share the same habitat make up a community
  • The community interacts with the environment in an ecosystem
  • The ecosystem is affected by biotic (living) factors and abiotic(non-living) factors
• Abiotic factors


  • Non-living factors that can interact with the community and affect the ecosystem
• Abiotic factors


  • Light intensity
  • Temperature
  • Moisture/ water levels
  • pH of the soil
  • Soil mineral levels
  • Direction and intensity of the wind
  • Levels of carbon dioxide
  • Levels of oxygen
• Change in an abiotic factor

  Can affect the whole community
• Effect of change in abiotic factor

  • If the soil water content is too low, plants will struggle to grow and animals who feed on the plants will be without food. This may cause them to migrate, use other food sources or in some cases cause death. This will have knock-on effects on the rest of the food chain.
• Biotic factors


  • Living factors that can influence an ecosystem
• Change in one biotic factor


  Can affect the whole community
• Effect of change in biotic factor

  • Grey squirrels were introduced into the UK in the late 1800s. They have since outcompeted the native red squirrels for food and other resources. As the number of grey squirrels increased, the number of red squirrels decreased.
• Interdependence


  Species within a community rely on each other to survive, e.g. for food, shelter, pollination, seed dispersal
• When all the species and environmental factors are balanced

  The population sizes stay the same and the community is said to be stable
• Effect of change in one species on food web

  • If there is a new disease in the ecosystem that kills all of the frogs, there will be less competition for grasshoppers so the bird population will increase in size. However, there will be less food for owls so their population size will decrease. Mice will also be eaten more by owls so their population will decrease. If there are less mice, there will be less food for hawks and foxes so their population sizes will also decrease.
• Adaptations


  • Features that make organisms more likely to survive in certain environments
• Types of adaptations


  • Structural
  • Behavioural
  • Functional
• Structural adaptations


  • Animals coloured to camouflage in environment
  • Animals in cold places have thick fat layer and small surface area to volume ratio
  • Animals in hot places have thin fat layer and large surface area to volume ratio
• Behavioural adaptations


  • Animals migrate to warmer places in winter
• Functional adaptations


  • Predators produce venom
  • Desert animals conserve water
  • Animals hibernate over winter
• Extremophiles


  Bacteria adapted to live in extreme conditions like high heat, high pressure, high salt
• Quadrats


  • Square frames of a known size, e.g. 1m2, that are usually divided into smaller segments
  • Placed on the ground and used to measure the abundance of certain small organisms in an area
• Using quadrats


  1. Count the number of the particular organism in the quadrat

  2. Estimate the percentage of the quadrat that is covered by the organism
• Counting organisms in quadrats

  • Counting the number of daisies is relatively easy
  • Counting the amount of grass would be incredibly difficult, so estimate percentage cover instead
• Calculating percentage cover of grass in a quadrat

  1. Count the number of squares that are more than half covered with grass

  2. Divide that number by the total number of squares in the quadrat

  3. Times the whole thing by 100
• Quadrats


  • Often used to randomly sample different areas so their species abundances can be compared, e.g. the amount of flowers in the sun compared to the shade
• Transects


  • Used to study the distribution of organisms across an area, in a straight line
  • A tape measure is laid out across the area that is to be studied
  • Can either count all the organisms that touch the line or place quadrats at regular intervals along the line and count/calculate the abundance of organisms at each point
• Using transects


  • Investigate how the abundance of marram grass changes as you move up a beach by placing quadrats at regular intervals along a transect
  • Notice how the abundance of marram grass increases with distance from the sea
• Making transect results more reliable


  Carry out many transects along the beach and calculate a mean abundance at each interval
• Required practical


  • Measure population size and species distribution using sampling techniques
• Calculating population size


  1. Divide the area that you want to sample into a grid and use a random number generator to select coordinates in the chosen area

  2. Find each coordinate and place a quadrat on the ground

  3. Count and record the number of organisms of the particular species in the quadrat

  4. Repeat using many randomly generated coordinates

  5. Calculate the mean number of organisms per m2

  6. Calculate the population size
• Investigating the effect of a factor on the distribution of a species

  1. Mark out a transect line along the ecological gradient using a tape measure

  2. At regular intervals along the line, place a quadrat on the ground and estimate the percentage cover of grass as well as measuring the light intensity using a light meter

  3. Continue until you reach the end of the transect

  4. Plot the light intensity against the percentage cover of grass on a graph to discover any trends in the data
• The distribution of organisms within a habitat can be affected by many factors and investigated using quadrats and transects
• Changes to the environment can also affect the distribution of organisms on a wider scale, such as seasonal, geographic or as a result of human activities
• Temperature changes, often due to climate change


  Can cause organisms to migrate
• The availability of water


  Can affect the distribution of organisms
• The composition of gases in the atmosphere


  Can affect the distribution of certain species
• All living things require water and nutrients (such as carbon and nitrogen) to survive, grow and reproduce
• Nutrients and water are constantly being recycled through abiotic and biotic parts of the ecosystem so they can be used to create future organisms