Capture - Mark - Recapture

Question 1

What is the process?

Answer 1

1) A large same of the species is caught and counted using an appropriate technique e.g. pitfall trap for beetles and sweep net for grasshoppers -S1
2) They are all marked, either permanent or semi permanent, that makes them no less likely to be predated i.e marking on the underside.
3) Released - allow sufficient time for the first same to mix throughout the whole population.
4) Resampled using the same trapping process, and the population size is estimated using the Lincoln index

    Initial sample     → S1 x S2 ←   Second sample                                 
                                  --------------
                                         r 
                                        ↓
                        Number recaptured

Question 2

What assumptions are made?

Answer 2

1) No significant gains or losses through emigration or immigration. Sample in a discrete area. e.g. one wood instead of one part of the wood.
2) No significant gains or losses through births or deaths
3) The trapping and marking process does not affect the animal in any way. i.e not more like to be predated.
4) The sample are given sufficient time to mix.
5) If the estimate is to be reliable, a large sample should be marked initially - between 10 and 30 % of the population