investigating populations Flashcards
how can the size of a population be estimated
randomly placing quadrants along a belt transect for slow, or non moving organisms
the mark release recapture method for motile organisms. The assumptions made when using the mark release recapture method.
what are the three sampling techniques
mark release capture, random sampling, systematic sampling
what are all the steps to mark release and recapture
you capture a sample of species and count them
mark them in a harmless way
release back into their habitat
wait then capture a second sample
count how many of the second sample are marked record the total captured in this second sample
input into calculation to estimate the population size
what assumptions are made with the release and capture method
the marked sample has had enough time to mix back in with the population
marking has not affected the individuals chance of survival
mark is still visible
no changes in population size due to births, death or migration
what are quadrats
an isolation of a standard unit of area for study of the number and distribution of an organism
what are the three ways of collecting datat using quadrats
count/density
percentage cover
frequency/proportion
what is count/density
the number of an organism in the quadrat
what is percentage cover
the percentage of the ground covered by an organism
what is frequency/proportion
the percentage of quadrat squares the organism is found in
Per cent area cover
Count each grid square where the plant appears in over HALF
Remember in this grid each square = 1%
% Frequency
Less accurate
Count how many squares the plant appears in
Remember in this grid each square = 1%
when is percentage area cover and frequency used
when individual species are difficult to count
Random sampling
Used to estimate a population size - organisms must be relatively evenly distributed
Divide the area up into a grid and assign each square coordinates
Use a random number generator (e.g. a calculator or random number table) to randomly choose numbers – this avoids bias
Use the numbers as coordinates to place the quadrats
Estimate % cover, count organisms or indicate if the organism is present or not
Large sample size ~50 and calculate mean
Transect sampling
Used to sample if the environment is changing (succession)
Place a line that is marked at regular intervals (i.e. a transect) across the area
Place a quadrat at each interval
Count or calculate the % cover of organisms in each quadrat
Repeat with more transects and calculate the average number of organisms at each distance.
Line transect
Run a 20m tape measure into the woods and identify the plant on the tape measure every 2m
OR put a quadrat down every 2 m and count/identify species in each quadrat (% cover, % frequency or number of individuals
