populations

Biology unit 4 (population and the enviroment) - revision notes

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population and ecosystem

Ecosystem = made up of all the interacting biotic (living) and abiotic (non-living)features in a specific area. Ecosystems are more or less self-contained functional units. Within ecosystem 2 major factors:

  • flow of energy through ecosystem
  • cycling of elements within the system

Population = group of interbreeding organisms of one species in a habitat.

Community = defined as all the populations of different organisms living and interacting in a particular place at the same time.

Habitat = place where a community of organism lives. within an ecosystem there are many habitats.

Ecological niche = describe how an organism fits into the enviroment. the role an organism has within an ecosystem.

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investigating populations

To study a habitat need to count numbers of individuals of a species in a given space = abundance Samples need to be representative of the whole population and any conclusions drawn from the findings need to be valid.Random sampling using frame quadrats or point quadrat.Systematic sampling along transect. Quadrats = three factor affect this :

  • size of the quadrat- depends on size of animal or plant
  • Number of sample quadrats to record within the study area- larger the number of sample quadrats the more reliable the results are.
  • The position of each quadrat within the study area- to produce statistically significant results.

Random sampling = used to avoid bias in collecting data, doing so means the data obtained is valid. The techniques of random sampling:

  •  Lay out 2 long tapes at right angles, alongside 2 sides of the study area
  •  Get a series of coordinates by using computer etc.
  • Place quadrat at the intersection of each pair of coordinate and record the species within it. 
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Systematic sampling along transects: sometimes more informative to measure the abundance and distribution of a species in a systematic rather than random way. Important where transition in communities of plants and animals takes place. Stages of zonation can be seen using a transect.

Measuring abundance: abundance = number of individuals of a species within a given space. It can be measured in several ways, depending on size of the species being counted and the habitat.

·       Frequency: likelihood of a particular species occurring in a quadrat. This method is useful where a species such as grass is hard to count. Gives a quick idea the species present and their general distribution within an area.

  • Percentage cover: estimate within a quadrat that a particular plant species covers. Useful where a species is particularly abundant or is difficult to count. Advantage of these situations = data can be collected rapidly and individual plant species doesn’t need to be counted.
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