Http://.

http://www.sciencenetlinks.com/Esheet.cfm?DocID=86

Sampling is a set of ways in which scientists try to accurately estimate the total population in community based upon a limited number of individuals

This is done because in most real life scenarios it is not possible to capture, collect or view every organism at once or over a period of time.

Look at a gram of healthy soil. One teaspoon of topsoil contains 5 billion bacteria in addition to all other organisms.

http://www.rhs.org.uk/advice/profiles0305/images/topsoil.jpg

Sampling is an estimate. It gives a solid approximation but…there is still a margin of error.

D= n/s(area)Number ÷ Space = Population Density

Take a number of samples from around the sampling site so as to be reasonably sure that the samples represent the site in general

the samples represent the whole…

It is necessary to take enough samples so that an accurate representation is obtainedIt is necessary to avoid bias when sampling

Type determined by the organisms and the physical nature of the habitat being sampled

Area of ground surfaceVolume of air, water or soilStandard units enable comparison of results

RawMark RecaptureSystematicStratifiedRandom

Raw Sampling Raw sampling assumes all individuals are

evenly spaced throughout the habitat. No adjustment or allowances is made for differences in distribution.

Count the individuals in a small area, the project to the entire area

Presence-absenceIdentify the presence or absence of a

designated speciesThis is the simplest method. And the least

precise. It is only used in a an initial study to determine what species are there. It does not estimate population

Mark-recaptureMark-recapture allows for differences in

distribution to be accounted for in a statistically significant method: (total number captured) X (number marked)/ total number marked recaptured

http://mampam.50megs.com/bok/markedbok.jpg

Often used when the area being studied is varied, not very large, or when time is available

Samples are taken at fixed intervals

Systematic samples are usually taken along a transect line marked by a tape measure

Transect- a line laid across an area

Transect LineA measured line is laid across the area in the

direction of the environmental gradientThe species touching the line can be recorded

along the whole length of the line (continuous sampling) or at specific points along the line (systematic sampling)

Transect line is more accurate then raw sampling, and more appropriate then mark recapture for plants and slow moving organisms.

It requires standard counting procedure, how far from the transect line individuals will be counted, abiotic conditions, and accurate mapping

Transect Line

http://www.uwsp.edu/cnr/cwes/forestree/images/ecolog1.jpg

http://ne.water.usgs.gov/html/Nawqa/pubs/posters/wetland95/photo5b.jpg

http://el.erdc.usace.army.mil/aqua/apis/ecology/image/img0006.gif

http://www.geobotany.uaf.edu/cryoturbation/photos2/transects/hv_t1_082201.jpeg

Similar to line transect but widens the sampling area

Transect line is laid out

Samples are taken by determining abundance or % cover in an area that is a defined distance from the line

Samples can be taken all the way along the line, at specific intervals or even randomly

4. Beltline Transect A belt line transect is similar to a transect

line except that it used alternating squares along a transect line to collect data from

4. Beltline Transect Gives good randomization of dataHas a specific fixed area to collect data fromIt is time consuming to measure correctly

and set up.

http://www.iol.ie/~carigeen/forest%20floor.jpg

belt transects measure the quantities of vegetation (within a quadrate frame placed along the transect line) and a line transect used to record the vegetation at different points (useful in succession)

So basically...belt = quantities of all vegetation in a % i.e ground coverageLine = species of vegetation present

Often used when there are small areas within a larger habitat that are clearly different

Strata- major differences within communities recognized before sampling begins

Often used when the area being studied is fairly uniform, very large, or when there is a limited amount of time available

Random = chosen by chance rather than according to a plan; all outcomes are equally likely

Samples are taken from different positions within a habitat and those positions are chosen randomly

Choose individuals or Place “sampling units” haphazardly

This is rarely completely random

OR…Assign numbers to the

areas or individuals to be sampled

Use a random number table to select which areas or individuals will be sampled