11.3 Sampling techniques

Why would you normally use more than one technique at each sampling point?

so a range of data can be collected

Animal sampling techniques (5)?

pooters, sweep nets, pitfall traps, tree beating and kick sampling

How should all living organisms be handled during sampling?

carefully and for as short a time period as possible

What must you do as soon as any sample animals have been identified, counted and measured if required?

release them back into the habitat at the point they were collected

What is a pooter used to catch?

small insects

How do you catch small insects using a pooter?

by sucking on a mouthpiece, insects are drawn into the holding chamber via the inlet tube

In a pooter - what prevents the small insects from being sucked into the mouth?

a filter before the mouthpiece

What are sweep nets used to catch?

insects in areas of long grass

Sweep netting: the 3 main aspects of sweeping to keep control?

sweep at same height, sweep at same depth and sweep for same length of time

Sweep netting: why must you sweep at the same height and depth each time?

different organisms might be at different depths/heights - therefore different number of organisms caught

Sweep netting: why must you repeat it at different times of the day?

different organisms out at different times

What are pitfall traps used to catch?

small, crawling invertebrates (e.g. beetles, spiders and slugs)

What is a pitfall trap?

a hole dug in the ground, which insects fall into

How deep must pitfall traps be?

deep enough so the insects can’t crawl out

What must you make sure you do to the hole acting as the pitfall trap?

level off the edge (so insects can still fall in it)

Why must pitfall traps be covered with a roof-structure propped above?

so that the trap does not fill with rainwater

How long are pitfall traps usually left?

24hrs (overnight - so that nocturnal species are also sampled)

What should you repeat pitfall traps along?

along a transect - repeat at least 5 times

What is tree beating used to take samples of?

the invertebrates living in a tree or bush

How is tree beating carried out?

large white cloth stretched out under the tree and the tree is shaken or beaten to dislodge the invertebrates - which will then fall onto the sheet to be collected and studied

What is kick sampling used to sample?

the organisms living in a river

How is kick sampling carried out?

river bank and bed is ‘kicked’ for a period of time to disturb the substrate and a net is held downstream for a set period of time to capture any organisms released into the flowing water

How are plants normally sampled?

using a quadrat

What animals can quadrats be used to sample?

slow-moving animals (e.g. limpets, barnacles, mussels, and sea anemones)

The two main types of quadrat?

point quadrat and frame quadrat

What is a point quadrat?

a frame containing a horizontal bar and at set intervals along the bar, long pins can be pushed through the bar to reach the ground

Point quadrat - what is recorded?

each species of the plant the pin touches

What is a frame quadrat?

a square frame divided into a grid of equal sections

Frame quadrat - what is recorded?

the type and number of species within each section of the quadrat

How should you use a quadrat to collect the most valid representative sample of an area?

following a random sampling technique

What do you place the quadrats systematically along a line or belt transect to study?

how the presence and distribution of organisms across an area of land varies

Species richness?

the number of different species living in a specific area

What should you use to try to identify all the species present in a habitat?

a combination of techniques

What should you do once you have identified all the species present in a habitat?

compile a list of each species identified and then the total number of species can then be calculated

Identification keys?

images to identify the organism, or a series of questions, which classify an organism into a particular species based on the presence of a number of identifiable characteristics

What are identification keys used to do?

enable scientists to accurately identify organisms

Species evenness?

how close in numbers the populations of each species in an environment are

Frame quadrats: the three main ways of sampling the population of plants living in a habitat?

density, frequency and percentage cover

Frame quadrats: what is the only absolute measure (not an estimate)?

density

Frame quadrats: how to measure density?

count the number of individual plants (in the species) in a 1m by 1m square quadrat to get the density per square metre

Frame quadrats: when do you use density?

if individual large plants can be seen clearly - to count individually

Frame quadrats: when do you use frequency?

when individual members of a species are hard to count (e.g. grass or moss)

Frame quadrats: how to find the frequency?

use the small grids within a quadrat, count the number of squares a particular species is present in (in an 100 square quadrat each small square represents 1%)

Frame quadrats: what is percentage cover?

an estimate by eye of the area within a quadrat that a particular plant species covers

Frame quadrats: why is percentage cover useful?

speedy - as lots of data can be collected quickly

Frame quadrats: when is percentage cover useful?

when a particular species is abundant or difficult to count

Why should samples be taken at a number of different points for each approach?

the larger the number of samples taken, the more reliable your results

What should you then calculate?

the mean of the individual quadrat results to get an average value for a particular organism per m²

How to calculate the mean value for a particular organism per m²?

add the individual quadrat results together, then divide by the number of samples taken

How to work out the total population of an organism in an area that has been sampled?

the mean value per m² x the total area

Why can it be difficult to accurately determine animal population sizes (2)?

animals are constantly moving through a habitat and others may be hidden

What technique is often used to estimate an animal population size?

a technique known as capture-mark-release-recapture

What is capture-mark-release-recapture?

capturing as many individuals of a species in an area as possible which are then marked and then released back into the community

Capture-mark-release-recapture: what is there time allowed for before the another sample of animals is collected?

time allowed for the organisms to redistribute themselves throughout the habitat

Capture-mark-release-recapture: what can scientists estimate by comparing the number of marked individuals with the number of unmarked individuals?

the population size

Capture-mark-release-recapture: the greater the number of marked individuals recaptured?

the smaller the population

How can species evenness in area then be calculated?

by comparing the total number if each organism present

What populations represent an even community and hence a high species evenness?

populations of plants or animals that are similar in size or density

How else can species evenness be expressed?

as a ratio between the numbers of each organism present

Abiotic factors?

the non-living conditions in a habitat - have a direct effect on the living animals that reside there

Why do scientists measure abiotic conditions at every sampling point?

to enable them to draw conclusions about the organisms present and the conditions they need for survival

What is used to measure wind speed?

anemometer

Wind speed unit of measurement?

m s^-1

What is used to measure light intensity?

light meter

Light intensity unit of measurement?

lx

What is used to measure relative humidity?

humidity sensor

Relative humidity unit of measurement?

mg dm^-3

What is used to measure pH?

pH probe

pH unit of measurement?

pH

What is used to measure temperature?

temperature probe

Temperature unit of measurement?

°C

What is used to measure the oxygen content in water?

dissolved oxygen probe

oxygen content in water unit of measurement?

mg dm^-3

Benefits of using these sensors to measure abiotic factors: what can be detected?

rapid changes (in conditions)

Benefits of using these sensors to measure abiotic factors: what is reduced?

human error in taking a reading

Benefits of using these sensors to measure abiotic factors: what can be achieved?

a high degree of precision

Benefits of using these sensors to measure abiotic factors: what can be done to the data?

can be stored and tracked on a computer