Measuring biotic factors

Question 1

1. Measuring abundance

Answer 1

Counting the no of organisms in a sample.
Usually we identify each organism found and so record the abundance of each species, but sometimes we count total abundance of all species.

Question 2

What method is used for animals to measure abundance?

Answer 2

Capture-mark-recapture method for counting the no of organisms since they can move.

Question 3

How is density worked out?

Answer 3

Diving teh abundance by the sampling area.

Number per sq m.

Question 4

Why can measuring abundance sometimes be difficult?

Answer 4

Sometimes its impossible to distinguish between closely-spaced individuals such as grasses.

Question 5

Definition of distribution

Answer 5

How the individuals are arranged or distributed in a habitat.

Question 6

a). Clumped distribution

Answer 6

Most common distribution of organisms, e.g. herds of antelopes.

Question 7

Why are organisms clumped?

Answer 7

1. As a defence against predators
2. or in hunting packs
3. or in social groups
4. or because their resources are localised such as a water hole

Question 8

b) Uniform distribution

Answer 8

When indviduals are as spread out as possible in a habitat,e,g hawks adn bears.

Question 9

When does uniform distrbution occur?

Answer 9

1. . Occurs when individuals defend a territory

2. or when there is competition for scarce, thinly-spread resources

Question 10

c) Random distrbution

Answer 10

Rarest distribution in nature.

Question 11

When does random distribution occur?

Answer 11

When the dispersal of young is random e.g. wind dispersed seeds and the location of each individual is independent of other individuals.
Only happens when resources are abundant and even, so there is little competition.

Question 12

2. Measuring Diversity

Answer 12

1. Sometimes we measure SPECIES DIVERSITY of an area and compare that with another area.
   2

Question 13

What is the best measure of diversity?

Answer 13

Simpson Diversity Index which requires us to measure the species richness and the abudance of each species.

Question 14

3. Measuring growth

Answer 14

Sometimes we compare the growth or size of similar organisms in different habitats over a period of time.

For animals, this might be measuring their mean length, or recording their mass.

For plants this might be measuring mean plant height, leaf area, no of leaves or plant mass (though this would mean uprooting and killing the plant).

In both cases it would mean we would have to take measurements at the beginning and end of the time period.

Question 15

4. Measuring Biomass. When do we need to measure dry biomass?

Answer 15

For studying productivity and making pyramids of biomass we need to measure dry mass.

Question 16

Why do we need to use dry biomass?

Answer 16

We need to use dry biomass since most of a living organism’s mass is made of water, which doesn’t contain energy

Question 17

How can you obtain dry mass?

Answer 17

A sample of organisms must be warmed in an oven at about 80C to evaporate the water, but not burn any organic material.
Sample is weighed at intervals until the mass no longer decreases, because all the water has evaporated.
This technique is drying to constant mass.

Question 18

Measurements you can take of plants with quadrats

Answer 18

1. Density
2. Species Frequency
3. Percent Cover
4. Point Quadrat
5. Abundance Scale

Question 19

How to measure density of plants using quadrats?

Answer 19

1. Count abundance

2. Divide abundance by area of quadrat

Question 20

Disadvantage of measuring density of plants

Answer 20

This measure is not appropriate when individual plants are difficult to identify.

Question 21

How to measure species frequency of plants?

Answer 21

1. Record the number of quadrats in which a species was found.
2. For e.g. if a species was found in 12 quadrats out of a total of 40, then the frequency is 12/40 = 30%

Question 22

How to measure percent cover of plants using a quadrat?

Answer 22

The % area of the quadrat covered by the species is estimated to nearest 5%.

Question 23

When is percent cover appropriate?

Answer 23

This is appropriate when it is difficult to identify individual plants such as grasses.

Question 24

Disadvantage of percent cover

Answer 24

Quite subjective

Since plants can be layered the total percentage cover can be more than 100%.

Question 25

Abundance scale using a quadrat for plants

Answer 25

Qualitative way to assess abundance. 
A = Abundant
C = Common
F = Frequent
O = Occassional
R = Rare

Question 26

Advantages of Abundance Scale

Answer 26

Quick way to collect the data

Question 27

Disadvantages

Answer 27

1. Subjective
2. Not quantitative
   Scale can be made semi- quantitaive by corresponding points to ranges of % covers.