19.5 Investigating populations

Question 1

What are the two methods of sampling techniques used in the study of habitats

Answer 1

1. Random sampling using quadrats

2. Systematic sampling along a belt transect

Question 2

What are the 3 factors to consider when using quadrats

Answer 2

1. The size of the quadrat - Depends on the size of the plants or animals being counted and how they are distributed
2. The number of quadrats to record within the study area. Larger number of quadrats = more reliable
3. Where quadrats are placed (random sampling must be used)

Question 3

How do we get a truly random sample (method of random sampling)

Answer 3

1. Lay out two long tape measures at right angles, along two sides of the study area
2. Obtain a series of coordinates by using random numbers taken from a table or generated by a computer
3. Place a quadrat at the intersection of each pair of coordinates and record the species within it

Question 4

What is abundace

Answer 4

The number of individuals of a species within a given area

Question 5

How do we measure abundance for species that dont move

Answer 5

1. Frequency - Likelihood of a particular species occurring in a quadrat
2. Percentage cover - estimate of the area within a quadrat that a particular plant species covers. It is useful when a species is particular abundant or difficult to count

advantages - collection is rapid

Question 6

What is necessary to obtain reliable results

Answer 6

1. Sample size is large

2. Many quadrats are used and the mean of all the samples is obtained

Question 7

What does a larger number of samples mean

Answer 7

That the result is more representative of the community as a whole

Question 8

What are mark-release-recapture techniques

Answer 8

Estimated population size = Total no. individuals in the first sample X total no. individuals in the second sample / number of marked individuals recaptured

Question 9

What is the principle behind mrc techniques

Answer 9

A known number of animals are caught, marked in some way, and then released back into the community. Later, a given number of individuals is collected randomly and the number of marked individuals is recorded

Question 10

What assumptions does the MRC technique have

Answer 10

1. The proportion of marked to unmarked individuals in the second sample is the same as a whole
2. The marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have time to do so
3. The population has a definite boundary so there is no immigration into or emigration out of the population
4. There are few, if any, deaths and births within the population
5. The method of marking is not toxic and nor does it make the individual look more conspicuous and therefore more liable to predation
6. The mark or label is not lost or rubbed off during the investigation