BIOLOGY FORM 4 CHAPTER 8 - DYNAMIC ECOSYSTEM PART 3

1. DYNAMIC ECOSYSTEM
PART 3
Part 2

2. How are populations
measured?

3. Population Density:
 is the number of individuals in a given area
or volume

4. How can the population density be found?
Impossible to count every organism in a
population

5. How is the problem solved?
ESTIMATE!!
How is an estimate done?
The size of a population is estimated by taking
random samples

6. Methods of estimating population size
OBJECTIVE METHODS
 Quadrats
 Capture-Recapture [Mark-release]

7. What are ‘Quadrats’?

8. A Quadrat is:
 a metal or wooden frame which forms a
square of known area such as 1m2

9. Various sizes of quadrats

10. 0.05  0.5 m quadrat
Smaller quadrats are used when…..
Zone is narrow.

11. Quadrats can be used to sample the flora

12. Can quadrats be used to sample fauna?
Slow moving / sessile
Topshells
Limpets
Barnacles

13. Fast moving
animals
BUT NOT:

14. How many quadrats?
Explain why it would be useless to take more
than 7 quadrats.

15. Quadrats provide calculation of three aspects of
species distribution:
1) Species density
2) Species frequency
3) Species cover

16. Species Density:
 the number of individuals of a given
species in a given area

17. 2) Frequency:
 a measure of the probability of finding a
given species with any one throw of a quadrat
in a given area
 e.g. if a species occurs once every ten quadrats, its
frequency is 10% [1/10 x 100]
 is obtained by recording the presence or absence of
a species in a quadrat

18. Frequency table
Organism 1 2 3 4 5 6 7 8 9 10 Total Frequency %Frequency
Quadrat throw
thrownquadratsofNo
organismcontainingquadratsofNo
Frequency
.
.

If percentage is required multiply frequency by 100

19. The bunchgrass species and the cattail species
have:
 an identical density of 7 plants per 36 m2.
 but different frequency.
Frequency of:
 bunchgrass (4/36 = 11%)
 cattail (7/36 = 19%)
Frequency depends on spatial distribution:

20. Frequency depends on quadrat size:
Frequency of:
 bunchgrass (4/36 = 11%)
 cattail (7/36 = 19%)
Frequency of:
 bunchgrass (3/9 = 33%)
 cattail (5/9 = 56%)

21. 3) Species Cover
 a measure of the proportion of ground
occupied by the species
 buttercup is covering about 6 boxes out of 25:
6
100 24%
25
 

22. Recording % Cover
Quadrat with a grid.

23. Recording % Cover
Subjective!!
Better if done by ONE person.

24. Species cover can be more than 100%
WHY?

25. Species cover can be more than 100%
WHY?
Overlap

26. RECAP
Quadrat Sampling technique
.
Density - abundance, measured by actual count, per unit area.
Counts are averaged when more than one sample is taken.
A) Density = Total no of individuals of a species in all quadrats
No. of quadrats x quadrat area
= 5+6+4+2+7 / 5x 1m2
Quadrat 1 2 3 4 5
No. of individuals 5 6 4 2 7

27. Quadrat Sampling technique
B) Percentage coverage
= aerial coverage of all quadrats(m2) x 100%
No. of quadrats x quadrat area
= 9+8+8+7+8 X100 % / 5 X 1m2
Quadrat 1 2 3 4 5
Coverage (m2) 9 8 8 7 8

28. Quadrat Sampling technique
 Frequency - the percentage of sample plots in which a
species or target group appears.
 C) Frequency
= No. of quadrats containing the species = 3/5
No. of quadrats
Quadrat 1 2 3 4 5
Frequency / / 0 / 0

29. Methods of estimating population size
OBJECTIVE METHODS
 Quadrats
 Capture-Recapture [Mark-release]

30. Capture-Recapture Method
How can fast moving
animals be sampled?
animals

31. Estimating numbers of mobile animals
 Involves:
 CAPTURE
 marking
 then capturing
another
sample of
individuals
Setting up traps to capture
animals

32. Estimating numbers of mobile animals
 Involves:
 MARKING
 then capturing
another
sample of
individuals

33. Marking methods
 Paint or dye, India ink
 Color band
 birds
 Unique markings
 Large mammals; keep
photo record
 Toe clipping
 Reptiles, amphibians,
rodents
(NPS 2000)
(Sutherland 1996)

34. Estimating numbers of mobile animals
 Involves:
 MARKING
 then capturing
another
sample of
individuals

35. This estimate of population size is:
 called the Lincoln index
Estimated total population =
(No. of organisms in 1st sample) x (No. of organisms in 2nd sample)
(No. of marked organisms recaptured)
 relies on the following assumptions:

36. Assumptions:
1. Organism mix randomly within the population.
2. Sufficient time must elapse between capture and
recapture to allow random mixing.

37. Assumptions:
3. It is applicable only to populations whose
movement is restricted geographically.
4. Organisms disperse evenly within the geographical
area of the population.

38. Assumptions:
5. Changes in population size as a result of
immigration, emigration, births and deaths are
negligible.

39. Assumptions:
5. Marking does not hinder the movement of the
organisms or make them conspicuous to
predators.

40. The photo below shows
a student using another
sampling technique.
The photo below shows a student using
another sampling technique.
a) Name the piece of apparatus being used to
sample plant density and diversity in the
field. (1)
Quadrat

41. The following photo shows three biology
students during fieldwork in a woodland area.
Explain why the
sampling equipment
shown in the diagram
cannot be used for
animals. (1)
Animals move out of the quadrat and so cannot
be counted.

42. Question:
1. The Humpback whale (Megaptera novaeangliae) used
to be common in the western North Atlantic, with an
estimated population of over 100 000. When commercial
whaling began, the population was reduced and it is
estimated that 90–95 % were killed. Populations are now
increasing because the species was classified as
‘threatened’ and given special protection.

43. Question:
a) Humpback whale populations are estimated from
photographs taken from ships or aircraft. They have very
distinctive natural markings so that individuals can be
distinguished.
The table shows the number of Humpback whales sighted
in two consecutive years.
Number photographed in year 1 1200
Number photographed in year 2 1157
Number of whales recognised in
both sets of photographs
120

44. Question:
(i) Use the Lincoln Index to calculate the population size of
Humpback whales in year 2. Show your working.
1 2
Population size =
m
n n
n

where n1= number seen in year 1
where n2= number seen in year 2
nm = number recognised in both years
1200 x 1157 = 11570
120

45. Question:
(ii) Suggest three reasons why this figure may not be
accurate. (3)
1. Individuals may not be recognised/be counted more than
once;
2. Relative not absolute numbers/only an estimate;
3. Immigration/emigration from area;
4. qualified reason for not being seen e.g.
underwater/diving/scared away by boats;
5. Births/deaths/caught by whalers;
6. May not mix randomly;

46. 2. The small black species of beetle shown in
the drawing is common in the grass zone.
It was decided to measure its population by
using the mark -release-recapture method.
Question:
a) Suggest how this beetle might be marked
before being released. (2)
Using waterproof paint – mark a
spot on underside of abdomen.

47. Pitfall traps were placed in the ground and left
overnight. The following morning 18 beetles
were captured. These were marked and
released. The traps were emptied again after 1,
2 and 4 days. The results are shown in the
diagrams.
b) Present the
results of this
investigation in a
suitable way. (3)

48. c) Use these results to
calculate the beetle
population. Show your
working. (2)
Day Number in second
sample (marked)
Total number in
second sample
1 4 16
2 3 12
4 4 16
Total 11 44
18 x 44 = 72
11

49.  The study of the relationships between groups
of organisms is called taxonomy, an ancient and
venerable branch of classical biology.
 Taxonomy is the art of classifying
things into groups— established as
a mainstream scientific field by
Carolus Linnaeus (1707-1778).

51. Taxonomic
group
Plant example Animal example
Kingdom
Phylum
Class
Order
Family
Genus
Species
Common
name
Plant
Tracheophyta
Angiospermae
Ranales
Ranunculaceae
Ranunculus
acris
Meadow
buttercup
Animal
Annelida
Oligocheata
Terricolae
Lumbricidae
Lumbricus
terrestris
earthworm
Animal
Chordate
Mammalia
Primates
hominidae
Homo
sapiens
human

52. Other member
(Panthera tigris)(Panthera tigris)
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Genus: Panthera
Species: P. tigris

53. Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Rosids
Order: Malvales
Family: Durionaceae
Genus: Durio zibethinus

55. 1
.
Has green colored body ......go to 2
Has purple colored body ..... go to 4
2
.
Has 4 legs .....go to 3
Has 8 legs .......... Deerus octagis
3
.
Has a tail ........ Deerus pestis
Does not have a tail ..... Deerus mg
4
.
Has a pointy hump ...... Deerus humpis
Does not have a pointy hump.....go to 5
5
.
Has ears .........Deerus purplinis
Does not have ears ......Deerus deafus

56. 58
Example of Dichotomous Key
1a Tentacles present – Go to 2
1b Tentacles absent – Go to 3
2a Eight Tentacles – Octopus
2b More than 8 tentacles – 3
3a Tentacles hang down – go to 4
3b Tentacles upright–Sea Anemone
4a Balloon-shaped body–Jellyfish
4b Body NOT balloon-shaped - 5