[19.5] investigating populations Flashcards
what is abundance?
the number of individuals of a species in a given space
what sampling techniques are used to study habitats?
- random sampling using quadrats
- systematic sampling along a belt transect
what are 3 factors to consider when using quadrats?
- the size of quadrat to use
- the number of sample quadrats to record within the study area
- the position of each quadrat within the study area
why are a quadrat’s 100 subdivisions useful and when should you count a plant as present?
- 100 squares is easy for percentage calculation
- only count a plant as present if it covers >50% of the square
method of sampling at random
- lay out 2 tape measures at right angles along 2 sides of the study area
- obtain a series of coordinates by using random numbers generated by a computer
- place a quadrat at the intersection of each pair of coordinates and record the species within it
how can reliable results be obtained?
- large sample size
- many quadrats are used
- mean of all samples is obtained
> the larger the sample, the more representative of the community as a whole the results will be
when should you use a transect?
if you wanted to look at systematic sampling at a transition between one environment to another
describe the mark-release-recapture technique
- a known number of motile animals are caught, marked in some way and then released back into the community
- some time later, a given number of individuals is randomply collected and the number of marked individuals is recorded
- the size of the population is calculated
how do you calculate the estimated population size in the mark-release-recapture method?
(total number of individuals in 1st sample × total number of individuals in 2nd sample) / number of marked individuals recaptured
what are some assumptions of the m-r-r technique?
- proportion of marked to unmakred individuals in 2nd sample is the same as the proportion of marked to unmarked individuals in the population as a whole
- marked individuals released from 1st sample distribute themselves evenly amongst the remainder of the population and have sufficient time to do so
- population has a definite boundary so there is no immigration or emigration in the population
- few, if any, deaths and births within the population
- method of marking is not toxic to the individual
- method of marking does not make the individual more conspicuous and therefore more liable to predation
- mark or label is not lost or rubbed off during the investigation
what are some limitations of the m-r-r technique?
- sample death / birth
- colour could rub off so estimate would be bigger
- sample from same area
- could have sample place, apparatus and method but confounding variables eg. weather, tide level
- need to leave enough time between taking 2nd sample
- sample could leave area entirely
