Population in ecosystem/ Sampling techniques
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Ecology
The study of interactions between organisms and their environment and determine their distribution and abundance
Two things ecologist look at in an ecosystem And what does it allow them to do?
Distribution - Where species are in an ecosystem Abundance - The number of species in an ecosystem Investigate how abiotic and biotic factors affect an ecosystem
Why do we use sampling techniques?
Impossible to measure exact number of organisms Time efficient More accurate Estimate
Sampling techniques
Quadrats, transects and MARK AND RECAPTUREEE
What sampling technique is used for non-motile/slow organisms
Quadrat and transects
What sampling technique is used for motile organisms
Mark -release and recapture
How to use quadrats to sample the abundance
1) Line two tape measures at a right angle to create a gridded area 2) Random number generate to get 2 coordinates 3) Place quadrat and collect data 4) Repeat 30 times and calculate mean 5) OR multiply the number in a singular quadrat by the area of the field
Advantages of quadrat
Random sampling prevents bias
When would you use a transect?
To see how distribution of species changes as the habitat changes
How do you use a transect?
1) Place transect at a right angle to shore line 2) Measure all along 3) See how distribution of organism changes
Quadrat measurements
Species frequency Local density Percentage cover
Species frequency
Probability that the species will be found in within a quadrat in the sample area (Number of quadrats species is present / Total number of quadrat) x 100
Local density
How many species per unit area Total number of individuals counted / Total area of quadrats
Percentage cover
This is used when it is difficult to count individual organisms such as grass or moss Quadrat is divided into 100 smaller squares Count squares where species occupy over half Percentage cover = Number of squares occupied
How to increase reliability / Accuracy of sampling techniques
More quadrats Repeat transect Calculate mean number per quadrat
Random sampling (Quadrat advantages)
Uniform distribution of species Representative of whole area
Systematics sampling (Transect)
Non-uniform distribution Not representative of whole area
How to use mark, release recapture method
1) First large sample is taken - Individuals are caught counted and marked in a way which wont affect survival 2) Marked individuals are returned to habitat and allowed to randomly mix within population 3) When a sufficient amount of time has passed another large sample is taken 4) Number of marked and unmarked individuals in the sample are counted 5) Proportion of marked to unmarked individuals is used to work out the population size
Formula for mark, release and recapture
N = (n1 x n2) / m2 N = total number of population n1 = Marked population in sample one n2 = marked and unmark in sample two m2 = marked in sample two