Random Sampling

• When do we sample a small area to estimate the total number of species in the total area?

  If an area is too large and a complex ecosystem such as rainforests.
• What is sampling?


  A method of investigating the abundance and distribution of species and populations.
• What are the two types of sampling?

  Random and systematic.
• What is random sampling?

  When the positions of the sampling points are completely random or due to chance.
• Why is random sampling beneficial?

  There will be no bias that may affect the results by the person sampling.
• What is systematic sampling?

  When the positions of the sampling points are chosen by the person carrying out the sampling.
• Why is systematic sampling unrepresentative?

  It may show bias towards or against certain areas and the person may deliberately place the quadrants in areas with the least species as it is easier to count.
• When is random sampling the best choice?

  If the sampling area is reasonably uniform or has no clear pattern.
• What is the distribution of a species?

  How it is spread throughout the ecosystem.
• What is the abundance of a species?


  The number of individuals of that species.
• What are used for sampling to mark off an area being sampled?

  Quadrats.
• How is random sampling used with quadrants to avoid bias?

  The area being sampled is converted into a grid format with coordinates then a random number generator is used to pick sets of sampling point coordinates.
• How do you calculate population density using a quadrat?

  Place the quadrant at the generated points and count the number of individuals in each one, then multiply the mean number of individuals per quadrant by the whole area.
• How do you calculate the abundance of a species using percentage cover using a quadrat?

  Place a quadrant at the coordinates and count the number of squares in each quadrant which the species occupies over half the square, 1 square counts for 1% abundance.
• What can the results form the quadrants be used to calculate?

  The predicted frequency and density of a species within an area.
• What is species frequency?


  The probability that the number of species will be found within any quadrant in the sample area.
• How do we calculate species frequency in % using quadrants?

  The number of quadrants the species was present in is divided by the total number of quadrates then multiplied by 100.
• What is species density?


  How many individuals of that species there are per unit area.
• How do we calculate species density using quadrants?

  The number of individuals counted across all quadrants is divided by the total area of quadrants.
• When is percentage cover estimated?

  When it is difficult to count individual plants or organisms.
• What can quadrants only be used for?

  Sessile and immobile species.