Quadrant method cant be used, as animals move around the capture recapture method is used instead. by tagging and marking animals it is possible to work out an estimate of the population.
the total number in a population can be estimated using the following formula:
Population size: number of animals tagged x number of animals recaptured / average number of tagged animals recaptured.
or for an abbreviation: MXN / N
the mark release recapture technique is based on a number of assumptions for accurate estimates of the total population to be calculated.
1. there is no population change through migration, births or deaths between the sampling periods.
2. all animals are equally able to be caught.
3. mark animals are not hampered in their ability to move and mix freely with the rest of the population.
there are problems with this method. if you are not careful with your tagging method you could cause the death of the animals that you tag. the tag may make the animal more likely to be caught by a predator. this could affect your result. when using traps to catch small mammals such as marsupial mice some of the animals become trap-shy and will not return to be captured. others enjoy the experience and return often to take the bait offered. other examples of tagging methods are leg bands on birds, paint spots on shell fish, colouring fur and ear tags.
trends in population estimates can be seen easily when abundance values have been graphed. examining trends can lead to inferences about the species and what abiotic or biotic characteristics they are most suited to.
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