2.2 - measuring populations

non-motile populations

organisms that do not move

measurement of non-motile populations

• quadrats

  • percentage cover

• transects

  • along a line

motile populations

organisms that can move independently

measurement of motile populations

• direct counts and sampling

• capture-mark-recapture

random sampling

selecting and studying areas at random to count individuals

+reduced bias

+equal chance of being selected

-might miss parts with particularly low/high population densities

systematic sampling

involves taking samples at regular intervals within study area

+straight forward method

+through and even coverage

-bias

belt transect sampling

systematic sampling along a line that runs through study area

+to study changes across an environmental gradient

+shows how population abundance varies along a path

capture-mark-release-recapture

1. capturing as many individuals

2. mark

   • without making them more visable to predators

3. release

   • allow time for reintegration with population

4. recapture as many as possible

5. count market and unmarked

6. use Lincoln index to estimate population size

*assumes no migration in or out of population

*assumes mixing of marked with unmarked individuals

Lincoln index

(M x N)/ R

M → nr caught and marked initially

N → nr of total recaptured

R → nr of recaptured marked