Module 5 of 5 · Text
Measuring the distribution and abundance of organisms
Distribution of organisms
- distribution = where the individual organisms are found within an ecosystem
- it is usually uneven throughout an ecosystem as organisms are generally found where the biotic and abiotic factors suit them most
- measuring it:
- a line or belt transect is used --> forms of systematic, non-random sampling
- systematic allow scientists to see how different abiotic factors affect the distribution of organisms
Abundance of organisms
- abundance = number of individuals of a species present in an area at a given time
- may fluctuate because:
- immigration and births increase the numbers of individuals
- emigration and deaths decrease the numbers of individuals
- measuring it:
- populations are estimated through sampling techniques --> never entirely representative of the whole population
- to increase accuracy, use large sample sizes
- measuring plant abundance:
- quadrat placed randomly in the area
- estimated number in population = number of individuals counted in sample / area of sample
- measuring animal abundance:
- capture-mark-release-recapture method
- capture as many individuals as possible in sample area
- mark or tag each individual
- release the marked individuals back into the sample area and allow time for them to redistribute themselves
- recapture as many as possible
- record the number of marked individuals and unmarked individuals
- use the Lincoln index to estimate population size
- estimated population size = (number of individuals in first sample * number in second sample) / number of marked recaptured individuals
- once the abundance is determined, scientists can work out the biodiversity by using Simpson's Index of Biodiversity