3.7.4 populations in ecosystems

• Community 


  All the different species that live in one area and interact with each other
• Ecosystem 


  All the living organisms found in one area, combined with non-living aspects of their environment. Can vary from very large to very small
• Biotic factors 


  Living features of an ecosystem
• Abiotic factors 


  Non-living features of an ecosystem
• Habitat 


  The place where an organism lives within an ecosystem
• Niche 


  The role of a species within its habitat, consisting of both biotic interactions and abiotic interactions
• Carrying capacity 


  The maximum size of a population an ecosystem can support
• Examples of abiotic factors

  Temperature

  Light

  pH

  Water/humidity
• Intraspecific competition 


  Between organisms of the same species
• Interspecific competition 


  Between organisms of different species
• What may organisms compete for?

  Food

  Water

  Shelter

  Mates

  Light
• Describe the pattern of a typical predator-prey relationship

  Prey is eaten by predator, resulting in predator population increasing and prey population decreasing. Fewer prey means increased competition for food, so predator population decreases. Fewer predators means more prey survives, and the cycle begins again
• How are quadrats used for estimating population size?

  Can be placed on grid coordinates, or at intervals along a belt transact. Results reported as either percentage cover or frequency. For slow-moving or non-motile organisms.
• How is mark-release-recapture used for estimating population size?

  A sample of a species is captured, marked, then released back into the same area they were caught. After a certain period of time another sample is captured, and the number of marked organisms are counted. For motile organisms
• Equation for mark-release-recapture

  Estimated population size = (total in first sample x total in second sample) / number of marked individuals recaptured
• What assumptions does the mark-release-recapture method make?

  Marked individuals distribute evenly

  No migration in or out of the population

  Few births or deaths

  Method of marking does nor affect survival

  Mark does not come off
• Why are ecosystems described as being dynamic?

  Populations constantly rise and fall

  Any small change can have a large effect

  Biotic and abiotic factors may alter the conditions of the ecosystem
• Primary succession 


  Where an area previously devoid of life is colonised by a community of organisms
• Summarise the process of primary succession

  Pioneer species can survive harsh conditions and colonise the area. They change abiotic factors of their environment. Over time, this allows more complex organisms to survive.
• What is the climax community and how is it reached? 


  The final stage of succession, where the ecosystem is balanced and stable. It id reached when the soil is rich enough to support large trees or shrubs, and the environment is no longer changing
• How might a species alter the environment that develops during succession?

  A species may improve the environment to make it more suitable for other species. Alternatively, a species may worsen the environment by making it less suitable for other species
• Conservation 


  The protection and management of species and habitats, in order to maintain biodiversity. Methods need to be adapted to the ecosystem in question
• How might succession be managed in order to aid conservation?

  Sometimes succession needs to be prevented in order to preserve an ecosystem at a certain point, e.g stopping moorland from progressing into spruce forest. This is called plagioclimax