Populations

Question 1

🔴️Population

Answer 1

All organisms of 1 species in a habitat

Question 2

Community

Answer 2

All of the populations of all the species

Question 3

🔴️How to use quadrats to estimate the number of bluebells in a field

Answer 3

• Lay out 2 tape measures at right angles.
• Then find coordinates using a random number generator
• Count number of plants in a quadrat and repeat this many times. Do this for different locations
• Calculate mean bluebells per quadrat
• Divide the mean by the area to get bluebells/m2.
• Multiply this by the total area of the field to estimate the bluebells present.

Question 4

🔴️How would you decide on the number of quadrats to use in order to collect representative data for number of plants

Answer 4

• Do enough to carry out statistical test
• Try to do a very large number to make sure the results are reliable
• but not too much as we need to make sure it can be done in the time allotted
• Calculate a running mean of species
• When the quadrats are enough, it levels out (if plotted): species against quadrat

Question 5

🔴️Explain why we should measure the population size immediately when using the MCR

Answer 5

• Rules out changes in the population
• This could be due to births/deaths/migration

Question 6

🔴️Ecological niche

Answer 6

• Refers to an organism’s feeding role (what it eats)
• And its abiotic role (where it lives in terms of conditions it needs)

Question 7

🔴️Assumptions made in Mark Capture

Answer 7

• Marking doesn’t wear off
• Marking isn’t toxic or conspicuous
• No births or deaths
• No immigration and emigration
• Mixes randomly with population

Question 8

🔴️How can you tell if 2 organisms are the same species

Answer 8

• Breed them together if they produce fertile offspring then they’re the same species

Question 9

What information is required in order to calculate the growth rate of a population?

Answer 9

• Birth rate and death rate
• Emigration and Immigration;

Question 10

Describe one method the scientists could have used to ensure that the sites were chosen without bias.

Answer 10

• Number the sites
• Use a random number generator

Question 11

Factors which lead to a decrease in the death rate in a human population.

Answer 11

• Improved medical care
• Improved quality and quantity food
• Improved sanitation so less disease

Question 12

When looking at survival curve, look out for:

Answer 12

1 Death and Birth rate.

2 Average life expectancy

Question 13

A girl collected 17 lizards and marked them before releasing them back into the same area. Later, she collected 20 lizards, 10 of which were marked.Calculate the number of sand lizards

Answer 13

No= (N₁ x N₂)/ N3

No= (17x 20)/10

Question 14

Using the mark-release-recapture method, describe how to estimate the number of one species of fish in the lake.

Answer 14

1 Capture sample using a trap. Count them, then mark and release (N1)

2. Make sure marking does not harm fish or make them conspicuous
3. Wait SUFFICIENT time so they reintegrate into population,

4 Then take second sample (N2) and count marked organisms (N3)

5. Calculation

Question 15

Why won’t the MCR method work if there are many births?

Answer 15

• The calculation only works if the population is constant.
• Births would change the population between the first and second sample

Question 16

How to use transect lines to measure the population of grass

Answer 16

1. Lie a tape measure from one side of the field to another
2. Place quadrats at regular intervals along the line
3. Count plants in quadrats and record where they touch transect
4. Calculate per M²

Question 17

Birth rate

Answer 17

Births per thousand per year

Question 18

Why won’t the MCR work if birds are forming separate territiories

Answer 18

1 Birds in territories not mixing with population

2 Territory sample not representative of population

Question 19

Death rate

Answer 19

Number of deaths per 1000 each year

Question 20

What factors affect birth rate?

Answer 20

• economic: availability of contraceptives/ pre-natal care / better nutrition of mother;
• education on family planning
• cultural/governmental influence on family size

Question 21

Changes that occur to birth and death rate during demographic transition

Answer 21

-Birth and death rate fall and then levels out (stabilises)

Question 22

Changes in the size of the population during a demographic transition

Answer 22

-Population size increases then levels out (stabalises)

Question 23

Ethical issues involving fieldwork?

Answer 23

• People walking may cause soil erosion.
• This can be combated by restricting where you walk to a specific area being studied

Question 24

Why does the pest population fluctuates due to predators

Answer 24

• As pest numbers increase more food for predators, so they increase;
• Increased predation of pests reduces numbers;
• Low number of pests results in less food for predators, so their numbers decrease;
• Low predator numbers allow pest population to reproduce as fewer are eaten;

Question 25

Define ecosystem

Answer 25

• All the living organisms in an area and their environment;

Question 26

What are transects and when do we use them?

Answer 26

• Line through habitat along which organisms are sampled and measurements are taken;
• We use them when there is a change in the environment
• And when we’re establishing pattern

Question 27

Benefits to organisms of having separate niches

Answer 27

• Reduce interspecific competition;
• For named resource e.g prey (food), water
• Reduces likelihood of one species eliminating another (competitive exclusion)

Question 28

Advantage of expressing birth rate in birth per 1000 people in a year

Answer 28

• Can compare different populations
• Can compare different years;
• Allows for variation at different times of year;

Question 29

Biotic and abiotic factor definition

Answer 29

• Biotic= living, biological factors
• Abiotic= non-living, environmental

Question 30

Habitat

Answer 30

• Physical place occupied by an organism

Question 31

Give two causes of a change in allele frequency other than the effect of selection

Answer 31

• Mutation;
• Small population
• immigration / emigration

Question 32

Suggest why population of goats E in spain do not breed with F?

Answer 32

• Different habitats;
• Different reproductive behaviour;
• Gamete incompatibility;

Question 33

Benefits of having own habitat

Answer 33

• mating
• raising of young
• predation less likely

Question 34

Adcantages of using % cover when measuring plant distribution

Answer 34

• Data can be collected rapidly;
• Does not require defining individual plants;