Investigating Populations: Mark|Capture|Release Flashcards
Why would a scientist use the mark|release|recapture method instead of a quadrat/transect?
Quadrats/transects are good to use when measuring the abundance of plant species and non - motile or slowing moving organisms but when measuring the abundance of motile organisms it is easier to use the mark|capture|release method as motile organisms are difficult to find and identify
Outline the method of mark|release|recapture:
First a known number of organisms is caught, counted and marked in some way.
Then the organisms are released. Some time later, a given number of organisms are again collected and the number of marked individuals is recorded.
The size of the population is then calculated
What is the equation used to calculate the estimated population size after conducting a mark-release-recapture method?
estimated population size = (total number of organisms in first sample x total number of organisms in second sample) ÷ number of marked organisms recaptured
What assumptions does this technique rely on? (6m)
1) There is an assumption that the proportion of marked to unmarked organisms in the second sample is the same as the proportion. of marked to unmarked organisms in the population as a whole
2) There is an assumption that the marked individuals released from the first sample distributed themselves evenly amongst the remainder of the population and have had enough time to do so
3) There is an assumption the population has a definite boundary so that there is no immigration into or emigration out of the population
4) There is an assumption there has been few, if any deaths and births within the population
5) There is an assumption that the method of marking does not make the organism more vulnerable to predation and the marking is not toxic
6) There is an assumption that the mark or label used on the organism is not lost or rubbed off during the investigation
An ecologist was estimating the population of sandhoppers on a beach. One hundred sandhoppers were collected, marked and released again. A week later 80 sandhoppers were collected, of which five were marked. Calculate the estimated size of the sandhopper population on the beach. Show your working
100 X 80 = 8000
8000 ÷ 5 = 1600
How might the following affect the final estimate of a population:
A) The marks put on the organisms captured in the first sample make them more easily seen by predators and so proportionally more are eaten than unmarked organisms
The individuals eaten will reduce the overall population, this will lead to a population over estimation, as there will be proportionally fewer marked individuals in the second sample
How might the following affect the final estimate of a population:
B) Between the release of marked individuals and the collection of a second sample an increased birth rate leads to a very large increase in the population
An influx of new organisms due to an increased birth rate will lead to a population over estimation as there will fewer marked in the second sample because all the ‘new’ organisms will be unmarked
How might the following affect the final estimate of a population:
B) Between the release of marked individuals and the collection of a second sample, disease kills large numbers of all types of organisms
There will be no difference because the proportion of marked and unmarked individuals killed should be the same
