C4.1 - estimating population sizes (1e)

Question 1

why is sampling necessary?

Answer 1

populations are often large and impractical to count, especially if the organisms are motile
- this means we must use methods to estimate population size, rather than counting every individual

Question 2

how can we estimate population sizes from sampled data?

Answer 2

population sampling involves identifying individual numbers in small areas and then extrapolating to estimate population totals

Question 3

why is random sampling necessary?

Answer 3

there needs to be randomness in sampling procedures to avoid selection bias that would cause an inaccurate estimate of the population size

Question 4

what is the relationship between sampling size and accuracy?

Answer 4

the larger the sampling area and the number of samples, the more accurate the population estimate

Question 5

what does random sampling cause?

Answer 5

random sampling, instead of measuring an entire population, results in sampling error, which causes an inaccurate estimate

Question 6

what is the sampling error when estimating population sizes?

Answer 6

the difference between the estimate of the population size and the true size of the whole population is the sampling error

Question 7

what are sessile organisms?

Answer 7

sessile organisms are immobile organisms, including both plants and animals, and is any species where the number of individuals can be counted

Question 8

what does standard deviation of a sample indicate?

Answer 8

standard deviation of the mean number of individuals per quadrat gives a measure of variation, showing how evenly the population is spread
- the larger the standard deviation, the less evenly the population is spread because there is more variation in the number of organisms counted in each quadrat

Question 9

how can a quadrat be used to estimate populations of sessile organisms?

Answer 9

1. use a 0.5 x 0.5, quadrat and create x and y co-ordinates for the area you are testing
2. generate random co-ordinates and place the quadrat in that area, counting the number of plants in several different areas
3. calculate the population by multiplying the mean number of species per m2 by the area of the field

Question 10

how do you calculate the Lincolm Index?

Answer 10

M x (N/R)

M - number of individuals marked initially

N - number of individuals recaptured

R - number of marked individuals recaptured

Question 11

how can we estimate population size of motile organisms?

Answer 11

using the capture-mark-release-recapture method
1. capture and count a sample of the population
2. apply a mark that will not affect the survival of the animal
3. release the organism into the environment
4. capture a second sample
5. calculate the Lincoln index to find the total population

Question 12

what are assumptions of the capture-mark-release-recapture method?

Answer 12

• assumes large enough sample size
• assumes no migration
• assumes no birth or deaths
• assumes marking doesn’t affect organisms survival
• assumes marked organisms don’t lose their marks
• assumes no mis-identification of species
• assumes marked and unmarked species have an equal chance of being captured