19 - Populations in Ecosystems

• What is meant by Population?

  A group of organisms of the same species living in the same habitat
• What is meant by Habitat?

  Part of an ecosystem in which particular organisms live
• What is meant by Community?

  All the populations of different species in the same area at the same time
• What is meant by ecosystem?

  A community and the non-living components of an environment (the biotic and abiotic factors). Ecosystems can range in size from the very small to the very large
• What is meant by Niche?

  An organism's role within an ecosystem, including their position in the food web and habitat. Each species occupies their own niche governed by adaptation to both abiotic and biotic conditions.
• What is meant by Abiotic Factors?

  Non-living conditions of an ecosystem
• What is meant by Biotic Factors?

  Impact of the interactions between organisms
• Which abiotic factors would impact the carrying capacity of a plant species population?

  1. Temperature
  2. Oxygen
  3. Carbon Dioxide Concentration
  4. Light Intensity
  5. pH
  6. Soil Conditions
  7. Water Availability
• What is meant by Interspecific Competition?

  When members of different species are in competition for the same resource that is in limited supply
• What is meant by Intraspecific Competition?

  When members of the same species are in competition for resources and a mate
• What are the key patterns of the predator-prey graph?

  The size of the predator and prey population both fluctuate, and there tends to be more prey than predators. The size of the population will always change first in the prey and after a lag period the predator population changes.

  
• Describe a method to accurately estimate the percentage cover of grass in a field.

  1. To randomly sample an area, place two 20m tape measures at right angles to create a gridded area to sample.
  2. Using a random number generator, such as a calculator, two values can be generated to use as coordinates in the gridded area created.
  3. The quadrat should be placed on the coordinate and a percentage cover could be estimated.
  4. This should be repeated at least 30 times to provide a representative estimate.
  5. Calculate a mean
• Describe a method of how to estimate the change in species richness along a rocky shore (from the shore line backwards towards the land)

  1. Place the tape measure at a right angle to the shore line
  2. Place the quadrat every 5 metres / every position
  3. Count the number of different species in each quadrat.
  4. Repeat by placing another 30 transects along the beach at right angles to the shore line.
  5. Calculate a mean for each quadrat position.
• What sampling method must be used to estimate the population size of motile organisms?

  Mark Release Recapture
• How would you ethically sample motile organisms?

  Sample/mark organism is a way that causes no permanent harm, does not impact predation or ability to reproduce
• What is the formula used to estimate the total population size when using mark-release-recapture?

  see below

  
• If 20 butterflies were initially caught and marked and then in the second sample 22 butterflies were caught, 9 of which had the markings on. What would be the estimated population size?

  49

  
• How would you estimate the population size of woodlice in a field?

  1. An initial sample of the population in question is captured.
  2. These individuals are then marked and then released back into the wild, and the number caught is recorded.
  3. These marked individuals are released and are left for a period of time to allow them to be randomly dispersed throughout the habitat.
  4. Then a second sample is captured.
  5. The total number captured in the second sample and the number recaptured with the marking is recorded.
  6. The size of the population is then estimated using the formula.
• What is meant by Succession?

  The change in an ecological community over time
• What is the difference between a primary and secondary succession?

  • A primary succession starts with a pioneer species colonising bare rock or sand.
  • In a secondary succession, there is disruption and the plants are destroyed. Succession starts again, but the soil is already created.
• What is a pioneer species and give an example?

  The first organism to colonise e.g. lichen
• What is meant by climax community?

  The final seral stage where the ecosystem is most stable
• What causes the abiotic factors to become less harsh during a succession?

  As organisms die and decompose it creates thicker and more nutrient-rich soil (humus).
• Why do species become outcompeted during a succession?

  The new species are better adapted to the environment
• What happens to the biodiversity as succession progresses?

  It increases
• How can managing succession be used to conserve habitats?

  By maintaining earlier stages in succession, and preventing a climax community, a greater variety of habitats are conserved and therefore a greater range of species.