sampling

sampling

what is sampling

• investigating a subset of a population or community

why do we sample

• impossible to count numbers of a particular species in a large area

• it is quick and easier method to estimate a population size or biodiversity

what is measured in sampling

• number of organisms

• particular characteristics of the organism

random sampling

• selecting individuals by chance

non random sampling

• not chosen at random

• divided into 3 techniques:

  • opportunistic

  • stratified

  • systematic

why are samples not always representative

• sampling bias

• chance

sampling techniques for small animals

• pooting

• sweep nets

• pitfall traps

• tree beating

• kick sampling

sweep nets

• used for flying insects on top of vegetation

• standardised method to obtain representative sample:

  • standard net size

  • sample breadth of sweep each time

  • if doing transect, 1 seep each step

  • if random, use the net number of sweeps each time

tree beating

• used for forest on mainly crawling and ,flying insects

• involves brushing insects on vegetation onto a sheet and beating/ catching insects on a sheet

• for both methods, insects can be transferred to a Ziplock bag

pooters

• used to collect small insects

• suck on a mouthpiece and insects are drawn into holding chamber via the tube

• a filter prevents them from being sucked into mouth

kick sampling

• used to sample invertebrates in streams/rivers

• hold net downstream from “kicking” sediment to release organisms

• net mouth is orientated facing the kicking site so any released organisms can be caught

• standardised by net size and number of kicks

pitfall traps

• used for sampling crawling insects that live on eg forest floor

• a cover on the trap protects from rainfall so caught insects don’t drown

what is used to sample plants

• quadrats