Populations in ecosystems

• Habitat


  • The place in an ecosystem where an organism lives
  • The range of physical, biological and environmental factors where a species lives
• Population


  Group of organisms of the same species living in the same habitat
• Community


  All the populations of different species in the same area/ habitat at the same time
• Ecosystem


  • A community and all the non-living components of the environment (abiotic factors)
  • Can range in size from very small tot very large
• Abiotic factors


  Non-living conditions of an ecosystem
• Biotic factors


  • Impact of interactions between organisms
  • The living components of an ecosystem
• Niche


  • An organisms role within an ecosystem
  • Including their position in the food web and habitat
  • Governed by their individuals adaptations to both abiotic and biotic conditions
• Carrying capacity


  The maximum population size an ecosystem can support
• Adaptations


  Features which increase an organisms chance of reproduction and survival
• Examples of abiotic factors

  • Temperature
  • Oxygen and carbon dioxide concentration
  • Light intensity
  • PH and soil conditions
• Population of organisms in an ecosystem in harsh abiotic conditions

  1. Smaller population

  2. As those with adaptations and ecosystems on an extreme end are more likely to survive and reproduce

  3. Only a small minority may have these adaptations

  4. Some species may die out - are unable to survive and reproduce - dont have the neccessary adaptations to survive on harsh abiotic factors
• Population of organisms in an ecosystem in less harsh abiotic conditions

  1. Larger size and greater range of species

  2. More species able to thrive and survive and reproduce

  3. Resulting in a larger population size
• Interspecific and intraspecific competition and predation

  Biotic factors - interactions between the living components of an ecosystem
• Interspecific competition


  • Members of different species compete with each other for the same limited resources
  • One of the two are better adapted and are likely to out-compete the less adapted species
• What might different organisms compete for?

  • Habitat
  • Limited food or water supply
• Intraspecific competition


  • Members of the same species are in competition with each other for the same resources and a mate
  • Depending on which organism is better adapted to the environment - one will be more successful and out-compete the other
• Competition for mates


  • Courtship rituals
  • Individuals that are fitter will have more energy to perform a better courtship ritual
  • Or may even have feathers or fur to attract a mate
• Predation


  Where an organism (predator) kills and eats another organisms (prey)
• Relationship between predator and prey populations

  • Interlinked
  • As the population of one changes so does the other
• Why might a scientist want to measure the size of a population?

  • To measure the impact of a changing environment
  • To protect plants and animals
• Why do scientist take samples and what must they be?


  • It would be too time-consuming and inaccurate to count every individual within a population
  • Samples need to be representative of the population size
• What makes a sample representative?


  • Taking multiple
  • Ensuring their a decent size - 30+
  • Making sure their random to avoid and bias
• Sampling method used for slow moving or non-motile organisms


  Sampling using a quadrat
• Two types of quadrat sampling

  • Random sampling
  • Belt transect
• When to use random sampling?

  • Studying an uniform distribution
  • Studying something like distribution of plants
• Describe how random sampling can be carried out

  1. Place two 20m tape measures at right angles to create a gridded area to sample

  2. Use a random number generator to generate two values which can be used as coordinates

  3. Place the quadrat at the coordinate

  4. Either count the number of species or estimate the percentage cover

  5. Repeat at least 30 times to provide a representative sample
• When to use a belt transect?

  • Uneven/ not uniform distribution
  • e.g rocky shore
• Two types of belt transects

  • Uninterrupted belt transect - the quadrat is placed at every position along a tape measure
  • Interrupted belt transect - The quadrat is placed at uniform intervals along the tape measure
• 3 types methods to estimate population size when using a quadrat

  • Density
  • Frequency
  • Percentage cover
• Describe how density can be used to estimate a population size


  Counting every individual from the species your sampling in the quadrat
• Describe how frequency can be used to estimate a population size

  1. Using a gridded frame quadrat with 100 squares

  2. Count how many out squares out of 100 contain the species your investigating

  3. Express that as a percentage out of 100

  4. If 25 squares contain the species - frequency is 25%
• Describe how percentage cover can be used to estimate population size

  The investigator estimates percentage of entire quadrat covered by the species
• Limitations and advantages of using percentage cover to estimate a population size

  • Quick
  • Subjective - lower accuracy of results
  • Can be improved by standardising the results
• Succession


  A change in an ecological community/ ecosystem over time
• Primary succession


  Succession which occurs with the colonisation of a pioneer species of bare rock or sand
• Pioneer species


  Organisms adapted to survive in harsh abiotic factors
• Importance of a pioneer species in succession

  • Through their death and decomposition they change the abiotic factors
  • It becomes less harsh and forms Humus
  • Overtime forms basic soil
• Describe how colonisation by a pioneer species can eventually become a climax community

  1. Pioneer species adapted to harsh abiotic conditions

  2. Through their death they make the environment less harsh/ hostile

  3. They form a thin layer of humus

  4. Mosses and smaller plans can then survive - they further increase the depth and nutrient content of the soil

  5. This pattern continues - as the abiotic factors continue to become less harsh larger plants can survive and change the environment further

  6. With each new species they may change the environment to become less suitable for the previous species - existing species are outcompeted by a new species colonising

  7. The final stage in a succession is known as the climax community, and this is dominated by trees.
• Secondary succession


  • When there is disruption and the plants in an existing ecosystem are destroyed
  • Succession starts again but the soil is already there so it doesn't begin from bare rock
• Conservation


  Protection and management of species and habitats in a sustainable way