sampling techniques Flashcards
(16 cards)
what are the three sampling techniques?
- random sampling
- transect sampling
- mark, release, recapture
what is random sampling used to figure out?
measure population size of slow moving + immobile organisms
what is the method for random sampling?
- choose area to be sampled and measure its area
- lay out tape measures to allow co-ordinates to be used (grid off area)
- use a random number generator to provide pairs of co-ordinates
- lay quadrat at co-ordinate, count organisms within the quadrat
- repeat process with as many quadrats as possible
- calculate mean number of organisms per quadrat
how to calculate abundance (random sampling)?
(mean from quadrats x area sampled)/ area of one quadrat
how can you count organisms in random sampling?
- number of individuals within quadrat
- the percentage cover of each species
when do you stop random sampling?
- calculate a running mean, plot mean of data, once mean no longer change by a large amount you have a realistic estimate
what is transect sampling used for?
- measure distribution of slow moving + immobile organisms
method of transect sampling?
- measure a straight line through an ecosystem (the transect)
- at regular intervals, place a quadrat
- count number of organisms in quadrat
- continue across the whole length of the transect
- plot data to show patterns
- repeat transect 3 times to get reproducible results
what is mark release recapture used for?
- estimate population size of mobile organisms
method for mark, release, recapture?
- live, mobile organisms are captured and marked and released back into the community
- some time after a number of individuals are collected randomly (recapture)
- the number of marked individuals are recorded
- formula used to estimate population size
what is the formula for population size? - MRR
(total captured and marked X total number captured second)/ number of marked in second sample
what are some of the assumptions we have when doing MRR?
- few deaths and births
- no immigration or emigration
- mark hasn’t rubbed off
- no time for hibernation
what should be done ethically when doing MRR?
marking should be non-toxic and doesn’t highlight prey
what should be controlled when sampling?
- standardised method e.g. sweep three times at shoulder height
- factors controlled e.g. time of day, time of year (seasons + hibernation may affect)
- abiotic factors controlled e.g. same weather, wind speed, humidity
- control sample area size + equipment used e.g. same quadrats/nets, same area size
sampling - ethical considerations?
- marking shouldn’t affect survival
- trampling of ecosystems can cause soil erosion + plant deaths
- smallest impact possible
risk assessment for sampling
- trips/falls = wear suitable footwear, not near cliffs or open water
- weather = check forecasts, wear appropriate clothing e.g. sun cream, waterproofs
- stings/bites = wear repellent, long sleeves + trousers, take allergy medication
