POPULATIONS AND ENVIRONMENT

Population equilibrium – Remember it! & Test it!

Population equilibrium – Remember it! & Test it!

  • Populations can be investigated by using a sample.
  • A frame quadrat can be used to count the number of species within a frame.
  • Line transects look at the number of species along a line.
  • Mark-capture-release is used for populations of mobile organisms.
  • A risk assessment is very important before carrying out a fieldwork investigation.
  • Population size can vary due to abiotic (non-living) or biotic (living) factors.
  • The human population growth rate is continuously increasing.
  • A population pyramid represents the various ages within a population.
  • A survival curve can be used to figure out the mean life expectancy within a population.

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TEST IT!

1.

Robins are small birds that live in wooded areas. An ecologist visited a wood in November and counted the robins in the area, using small metal rings to mark the birds he caught. He then returned two week later, marking down the birds already caught separately.

First sample: 28 captured and marked.

Second sample: 16 marked robins and 19 unmarked

a) What is this sampling method he used called?

b) Estimate the size of the robin population. Show your working.

c) Robins form pairs and breed between March and May. The young birds then leave the nest between June and July and the rest of the year robins flock and feed in the woods and close to gardens. Why would using the method used here not give reliable results of the robin population:

i. in June?
ii. in March?

2.

A group of scientists wanted to calculate the number of organisms at three sites along a seashore by using quadrats. In their preliminary investigation they composed a table of the total number of species with an increasing number of quadrats.

Total no. of species

Number of quadrats

8

20

26

43

45

57

60

61

62

65

2

4

8

9

11

12

14

16

18

28

a) Why would 10 quadrats not be an appropriate number to use?

b) Why would 25 not be an appropriate number to use?

3.

a) What is meant by birth rate?

b) Life expectancies can be different in different countries. For example, the life expectancy for people living in the UK is high than that in Sudan. Suggest why this might be the case.

ANSWERS

1.

a) Mark-capture-release

b) Use:

(organisms caught first time x total number of organisms caught second time)

marked organisms caught second time

(28 x 35) 16 = 61.25 = 61 (2sf)

c)

i. The population changes as young birds leave the nest
ii. The birds are living in territories and so not mixing with other birds. This means there’s a high chance of catching the same birds again. A territory isn’t representative of the population.

2.

a) The number of species is still increasing.

b) The results are getting closer so the same result can be had with less quadrats thereby saving time and effort.

3.

a) Births in a given number of the population in a given time.

b) Answers include:

i. Vaccination programmes are better in the UK
ii. Infectious disease is more common in Sudan
iii. Many people have a better diet in the UK
iv. Sanitation is better in the UK