sampling techniques Flashcards
(40 cards)
why would you use more than one sampling technique at each sampling point
to a collect a range of data
why is it difficult to sample animals
smaller animals aren’t easy to see and difficult to count as they often move too quickly to count accurately. larger animals can detect the presence of humans before we see them and hide them away
how else can you note presence of large animals
by careful observation e.g. footprints, easily identified droppings
what is a sweep net
used to catch insects in areas of long grass
how to use a sweep net
walk through habitat with a stout net and you sweep the net through the vegetation in wide arcs. any small animals such as insects will be caught in the net. you empty the net onto a white sheet to identify them. you need to be quick and careful to count and identify them before they crawl away
how would you use a sweep net to collect from trees
collecting from trees using a sweep net is unlikely to work well - spread a white sheet out under a branch and knock the branch with a stout stick. the vibrations dislodge any small animals which fall to the sheet. you need to quickly identify the animals before they crawl or fly away
what are pooters used for2wed
used to catch small insects. by sucking on a mouthpiece, insects are drawn into the holding chamber via the inlet tube. a filter before the mouthpiece prevents them from being sucked into the mouth
what are pitfall traps used for
used to catch small, crawling invertebrates such as beetles, spiders and slugs. a hole is dug into the ground which insects can fall into. it must be deep enough that they can’t crawl out and and covered with a roof-structure propped above so the trap doesnt fill with rainwater. the traps are normally left overnight, so nocturnal species are also sampled
whats tree beating
used to take samples of invertebrates living in a tree or bush. a large cloth is stretched out under the tree. the tree is shaken or beaten to dislodge the invertebrates. the animals will fall onto the sheet where they can be collected and studied
whats kick sampling
study organisms living in a river. river bank and bed is kicked for a period of time. a net is held just downstream for a set period of time to any organisms released into the flowing water.
tranquiliser
fast/large/more dangerous animals can be sedated prior to study. tissue samples can also be taken to observe genetic biodiversity. animals should be handled carefully for as short a period as possible and released where they are captured
whats a Tullgren Funnel
works by creating a dessication gradient over the sample such that mobile organisms will move away from the dry environment and fall into a collecting vessel where they are collected
whats capture-mark-release-recapture
1) capture a sample of animals, note the number
2) individuals are harmlessly marked and then released
3) time is allowed for the organisms to redistribute
4) recapture and count how many are caught now
5) note numbers of recaptured (marked) individuals
how to work out the number of species using CMRRC
total population =
number of animals in 1st sample x number of animals in 2nd sample/number of animals marked in 2nd sample
what can CMRRC
by comparing the number of marked with number of unmarked individuals - scientists can estimate population size. the greater the number of marked individuals recaptured, the smaller the population
what are the assumptions made when sampling
- no deaths/births/migration
- sampling methods are the same each time
- conditions are the same for when each sample is taken (conditions can be varied to compare population size in different seasons etc)
how are plants normally sampled
its normally sampled using a quadrat which can be used to pinpoint an area in which the samples of plants should be collected - used to sample slow moving animals such as limpets, barnacles, mussels etc
what are the two types of quadrats
- point quadrat
- frame quadrat
what is a point quadrat
consists of a frame containing a horizontal bar. at set intervals along the bar, long pins can be pushed through the bar to reach the ground. each species of plant the pin touches is recorded
what is a frame quadrat
this consists of a square frame divided into a grid of equal sections. the type and number of species within each section of the quadrat is recorded
how should quadrats be used to collect a valid representative sample of an area
they should be used following a random sampling technique.
how can quadrats be used to study how the presence of organisms across an area varies
the quadrats can be placed systematically along a line or belt transect
how to calculate species richness
write a list of all the species identified and then the total number of each species and then the total number of species
what are identification keys used for
accurately identifying organisms which may contain images to identify the organism which classify an organism into a particular species based on the presence of some identifiable characteristics
