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Populations and Ecosystems

  • Living organisms for communities through which energy is transferred and elements are recycled.
  • This is known as ecology; this is the study of inter-relationships between organisms and their environment.

Key Terms:

  • Ecosystem - All the organisms living in a particular area and all the abiotic and biotic facters which make up that area.
  • Habitat - A place where an organism lives.
  • Population - All the organisms of one species living in the same habitat.
  • Community - All species of organisms living and interacting within the same ecosystem.
  • Abiotic Factors - All non-living factors of the ecosystem, e.g. temperature, PH of soil, light ect.
  • Biotic factors - The living factors of the ecosystem, e.g. predation, reproduction and competition.
  • Ecological niche - Where an organism recieve all it's abiotic an biotic factors needed to surive, reproduce and maintain a viable population.
  • Fundermental niche - where an organisms can survive but doesn't get all its abiotic and biotic factors which are needed.
  • Adaptation - A feature that members of a species have that increases their chances of survival and reproduction, e.g. giraffes have long necks to help them reach for the vegetation that high up.

Investigating Populations

  • To study a habitat, it is often necessary to count the number of indivduals of a species in a given space; this is known as abundance.
  • It its virtually impossible to identify and count every organism within the community; it would also be very time consuming and damaging to the habitat being studied. 
  • Small samples of the habitat are usually studied in detail and as long as these samples are representative of the habitat as a whole, any conclusions can be drawn from the findings and will be valid.
  • There are a number of sampling techniques used in the study of habitats, these are:
  • Random sampling using frame quadrats or point quadrats.
  • Systematic sampling along transects.


There are three factors to consider when using quadrats:

  • The size of the quadrat - this will depends on the size of the plants or animals being counted and how they are disributed within the area, i.e. larger species will require larger quadrats.
  • The number of sample quadrats tow record within the study area - the larger the number of sample quadrats the more reliable the results will be. The greater the number of different species present in the area being studied, the greater the number of quadrats required to produce valid results.
  • The position of each quadrat within the study area - to produce statistically significant results, random sampling must be used.

Random Sampling: 

  • It is important that sampling is random to avoid research bias when collecting that data, as it ensures that the data obtained is valid.
  • The method of random sampling is as follows:
  • Lay out two long tape measures at right angles, along two sides of the study area, to form a grid of co-ordinates.
  • Obtain a series of co0ordinates by using random numbers taken from a table of random numbers,


Faiza Azam


thank you made me realise our teacher has not given us sufficient notes 

Tilly - Team GR


Very good quality notes. They included everything I need. Very helpful thanks!



A detailed set of notes that usefully describe the key terms used in ecology and the way ecosystems are investigated, by sampling and measures of abundance. It would be useful to team these up with a set of diagrams that could be used to illustrate the different type of transects since students are often asked to describe how to study an area and a good relevant annotated diagram is always awarded marks.

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