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ECOLOGICAL SAMPLING METHODS

ECOLOGICAL SAMPLING METHODS. Importance of Sampling. If we want to know what kind of plants and animals are in a particular habitat To enable you to monitor changes and thus be made aware of activities which may be causing possible extinctions etc. How many there are of each species.

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ECOLOGICAL SAMPLING METHODS

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  1. ECOLOGICAL SAMPLING METHODS

  2. Importance of Sampling • If we want to know what kind of plants and animals are in a particular habitat • To enable you to monitor changes and thus be made aware of activities which may be causing possible extinctions etc. • How many there are of each species. • usually impossible to go and count each and every one present • It would be like trying to count different sizes and colours of grains of sand on the beach.

  3. Importance of Sampling • Problem is usually solved by taking a number of samples from around the habitat • Making the necessary assumption that these samples are representative of the habitat in general. • In order to be reasonably sure that the results from the samples do represent the habitat as closely as possible, careful planning beforehand is essential.

  4. Importance of Sampling • Samples are usually taken using a standard sampling unit of some kind. • Ensures that all of the samples represent the same area or volume (water) of the habitat each time. • Sampling unit is a quadrat. • Quadrats consist of a square frame, the most frequently used size being 1m . • The purpose of using a quadrat is to enable comparable samples to be obtained from areas of consistent size and shape.

  5. Importance of Sampling

  6. Ways of Taking Samples • There are two main ways of taking samples. • 1. Random Sampling. • 2. Systematic Sampling (includes line transect and belt transect methods).

  7. Random Sampling • When to use • when the area under study is fairly uniform • very large • there is limited time available. • large numbers of samples/records are taken from different positions within the habitat. A quadrat frame is most often used for this type of sampling.

  8. Systematic Sampling • Samples are taken at fixed intervals, usually along a line. • This normally involves doing transects • a sampling line is set up across areas where there are clear environmental gradients. • example you might use a transect to show the changes of plant species as you moved from grassland into woodland, or to investigate the effect on species composition of a pollutant radiating out from a particular source .

  9. Types of Transects • Line Transect Method: A transect line can be made using a nylon rope marked and numbered at 0.5m, or 1m intervals, all the way along its length • Species touching the transect are counted.

  10. Types of Transects • Belt Transect Method: Similar to the line transect method but gives information on abundance as well as presence, or absence of species. • consider it a widening of the line transect to form a continuous belt, or series of quadrats.

  11. Ways of Counting Animals • Direct Observation • Capture, Mark, Release • N = MC/R • where • N = Estimate of total population size • M = Total number of animals captured and marked on the first visit • C = Total number of animals captured on the second visit • R = Number of animals captured on the first visit that were then recaptured on the second visit

  12. What do we do with these counts? • Species Density/Volume: • #/area or volume • Species Frequency: • Total Number of Organism/Total Number of Quadrants • Species Diversity • # of Quadrants species is present in X 100 / Total number of quadrants

  13. What do we do with these counts? • Species Richness (R): • The species richness is based solely on the number of species found in the given area and does not reflect the relative dominance of species. The formula is: • R = s Where: s = the number of species

  14. What do we do with these counts? • Shannon-Wiener Index (H) • This index is determined by both the number of species and the even distribution of individuals among those species (relative dominance). It indicates the degree of uncertainty of predicting the species of a given individual picked at random from the community. In other words, if the diversity is high, you have a poor chance of correctly predicting the species of the next individual picked at random. • H = - sum(Pi ln[Pi]) • Where: Pi (relative abundance) = ni/N • Where: ni = number of individuals in species i • N = total number of individuals in all species • H (the uncertainty of predicting the species) will range from 0 for a community with a single species, to over 7 for a very diverse community.

  15. What do we do with these counts? • Species Evenness • Using species richness (R.) and the Shannon-Wiener index (H), you can also compute a measure of evenness. • The formula is: • E = H/ln(R) • Evenness (E) is a measure of how similar the abundance of different species are. When there are similar proportions of all species then evenness is one, but but when the abundance are very dissimilar (some rare and some common species) then the value increases.

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