7.4 Investigating population abundance using sampling

Question 1

Define abundance

Answer 1

the number of organisms in a habitat

Question 2

Give two reasons why it is not possible to count all organisms in a habitat?

Answer 2

Too time consuming

Likely to damage habitat

Question 3

Name two types of quadrat

Answer 3

Frame/grid quadrat

Point quadrat

Question 4

How are frame/grid quadrats used?

Answer 4

Square frame of known length divided into a grid

Grid placed in habitat and abundance and/or frequency of species in grid recorded

Question 5

How are point quadrats used?

Answer 5

Bar of known length, legs either end, holes at set intervals along bar
Pins placed through holes
Any species touched by pin is recorded

Question 6

Name three factors to be considered when using a quadrat

Answer 6

Size of quadrat
Number of quadrats used
Placing of quadrats

Question 7

How does the size of the quadrat used differ when considering the size of the organism?

Answer 7

Larger organism, use a larger quadrat

Question 8

How does the size of the quadrat used differ when considering the spread of organisms within a habitat? Why?

Answer 8

Uneven spread, larger number of small quadrats

Provides a more representative sample

Question 9

How are issues related to counting organisms within a habitat overcome?

Answer 9

Using small samples that are representative so estimated judgements can then be made about species abundance

Question 10

What effect does the number of quadrats used have?

Answer 10

More quadrats used, more reliable results because the sample is more representative

Question 11

How does the number of organisms within a habitat factor in when considering how many quadrats to use?

Answer 11

Larger number of species in habitat, more quadrats required to obtain representative sample

Question 12

How does the number of quadrats used have to be considered when looking at what other factor?

Answer 12

Number of quadrats undertaken has to factor into time available for sampling

Question 13

Name two ways that quadrats can be placed in a habitat.

Answer 13

Random sampling using the grid co-ordinate method

Systematic sampling using a transect line

Question 14

Why would you use each method of placing quadrats in the habitat?

Answer 14

Random sampling- to obtain statistically significant results

Systematic sampling- to obtain results about a changing habitat/habitat boundaries

Question 15

Describe the grid co-ordinate method.

Answer 15

Two long tape measures at right angles of study area
Obtain series of coordinates using random number generator
Place quadrat at intersection and record

Question 16

What is a transect?

Answer 16

A tape or string of known length

Question 17

Give three methods of systematic sampling using a transect.

Answer 17

Line transect- record frequency and/or abundance of organisms transect touches
Belt transect- quadrats placed along whole length of transect directly next to each other, record frequency and/or abundance of organisms within each
Interrupted belt transect- quadrats placed at regular, known intervals along transect

Question 18

What three things can we determine from sampling?

Answer 18

Species frequency- % chance of finding species in any quadrat
Species density- number of organisms/m2
Species cover- % area occupied by certain species

Question 19

What is the technique mark-release-capture used for??

Answer 19

Used to sample organisms that move to estimate abundance of a population

Question 20

Give the seven steps to work out the estimated population abundance using the mark-capture-release method

Answer 20

1. Humane method used to catch known number of organisms
2. Organisms marked
3. Organisms released
4. Given time to redistribute back within population
5. Organisms caught again
6. Number of marked individuals in sample recorded
7. Estimated population abundance = (number caught in first sample x number caught in second sample)/
   number of marked individuals in second sample

Question 21

Give three examples of humane trapping methods.

Answer 21

Longworth trap
Pitfall trap
Sweep netting

Question 22

What six assumptions are made when using the mark-capture release technique?

Answer 22

Proportion of marked to unmarked individuals in sample two is the same as proportional number of unmarked individuals in population
Marked individuals redistribute selves evenly through population
No emigration/immigration
Few births/deaths
Marking method is non toxic and doesn’t affect organism
Marking doesn’t rub off