1 / 27

Sampling Techniques

Sampling Techniques. http://www.sciencenetlinks.com/Esheet.cfm?DocID=86. What is Sampling?. 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. Why?.

nuru
Télécharger la présentation

Sampling Techniques

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. What is Sampling? • 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

  3. Why? • 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

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

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

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

  7. Necessities… the samples represent the whole… • It is necessary to take enough samples so that an accurate representation is obtained • It is necessary to avoid bias when sampling

  8. SAMPLING UNITS • Type determined by the organisms and the physical nature of the habitat being sampled • Area of ground surface • Volume of air, water or soil • Standard units enable comparison of results

  9. Examples of TYPES OF SAMPLING • Raw • Mark Recapture • Systematic • Stratified • Random

  10. Types 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

  11. Types Presence-absence • Identify the presence or absence of a designated species • This 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

  12. Types Mark-recapture • Mark-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

  13. SYSTEMATIC SAMPLING • Often used when the area being studied is varied, not very large, or when time is available • Samples are taken at fixed intervals

  14. Types of transect sampling

  15. How to sample systematically • Systematic samples are usually taken along a transect line marked by a tape measure • Transect- a line laid across an area

  16. Types Transect Line • A measured line is laid across the area in the direction of the environmental gradient • The 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)

  17. Types • 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

  18. http://www.uwsp.edu/cnr/cwes/forestree/images/ecolog1.jpg http://el.erdc.usace.army.mil/aqua/apis/ecology/image/img0006.gif Types Transect Line http://ne.water.usgs.gov/html/Nawqa/pubs/posters/wetland95/photo5b.jpg http://www.geobotany.uaf.edu/cryoturbation/photos2/transects/hv_t1_082201.jpeg

  19. Belt transect method • Similar to line transect but widens the sampling area • Transect line is laid out

  20. Belt transect method • 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

  21. Types 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

  22. Types 4. Beltline Transect • Gives good randomization of data • Has a specific fixed area to collect data from • It is time consuming to measure correctly and set up.

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

  24. Belt transects vs Line transects • 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

  25. STRATIFIED SAMPLING • Often used when there are small areas within a larger habitat that are clearly different • Strata- major differences within communities recognized before sampling begins

  26. RANDOM SAMPLING • 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

  27. How to sample 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

More Related