Investigating populations
• A critical appreciation of some of the ways in which
the numbers and distribution of organisms may be
investigated.
• Random sampling with quadrats and counting along
transects to obtain quantitative data.
• The use of percentage cover and frequency as
measures of abundance.
• The use of mark–release–recapture for more mobile
species.
Investigating populations 2
• In the context of investigating populations,
candidates should
• carry out experimental and investigative activities,
including appropriate risk management
• consider ethical issues arising when carrying out
fieldwork, particularly those relating to the
organisms involved and their environment
• analyse and interpret data relating to the
distribution of organisms, recognising correlations
and causal relationships
• appreciate the tentative nature of conclusions that
may be drawn from such data.
Variation in
population size
• Population size may vary as a result of the
effect of abiotic factors
• interactions between organisms: interspecific
and intraspecific competition and predation.
In relation to exam questions
Population
• Lots of 2 mark questions looking at the
definitions of the key terms.
• Look out for graph questions on predator prey
relationships and competition.
• Be ready to analyses graphs and relate your
knowledge to the situation presented for the
longer data questions.
C
D
E
A
B
With reference to the drawing, explain the meaning of
the terms
(i)
community;
.........................................................................................................
(ii)
population.
...........................................................................................................................(3)
(a)
(b)
Describe how you could use point quadrats to investigate the
distribution of plants at the edge of a pond. (3)
1.(a)(i)All
organisms living in a particular place;
(ii)
All the organisms of one particular species;
Both examples illustrated with reference to drawing;
3
(b) Transect from water onto bank;
Point quadrat frame placed at regular intervals;
Record species touching points;
Calculate percentage/process with kite diagram/
use statistical test to show..;
max 3
Investigating populations
• A mixture of marks and data related questions.
• Can range from 6-15 mark questions.
• Sampling techniques will most likely feature in
the question.
• Make sure that you can describe the different
sampling techniques.
• These questions are most likely to test your
analytical skills so get ready to draw a
conclusion.
• Explain how a frame quadrat is used to find
percentage cover of a species of plant in a
habitat. (3)
• Ground beetles are large black insects. The markrelease-recapture method can be used to
estimate the ground beetle population on a
roundabout. Describe how. (5)
• Describe the techniques you would use to obtain
reliable data in order to compare the sizes of the
populations of the snail in the muddy area and in
the area covered by vegetation. (3)
• Describe one way in which you could place the
quadrats randomly in a field. (2)
Answer
(a)suitable number of quadrats used;
(many/ large number/ 10 minimum)
count all the squares occupied (by the leaves of) one
species; reference to randomising;
description of a method of randomising any 3
b) 1Sample of ground beetles captured and counted (a);
• 2 Released and second sample captured;
• 3 Count total number of beetles (B) and number marked
(b);
• 4 Total population (A) estimated from the relationship ;
• 5 Detail of method e.g. pitfall trap/marking with tippex;
• 6 Refinement to ensure greater accuracy e.g. large
number/ marking in position such that does not affect
survival; 5 max
c)use of large numbers of quadrats in each area (if
number stated then 10+);
random sampling method (e.g. grid + random
numbers)/systematic sampling method (allow
regular sampling along a transect); counting.
OR
(allow capture/recapture method mark and
release; recapture; calculate proportion of
marked snails in second sample)
3
D) Use of grids/coordinates;
Table of random numbers;
2
Starter Questions
1. An investigation is being conducted into the
population size of dragonflies along the bank
of a river. The bank is steep and there has
been a high level of rainfall.
a) Give one risk posed by the investigation, and
suggest how this risk can be reduced.
Previous studies have suggested that a population
of water voles, which are a protected species,
may live in burrows on the river bank.
b) Explain why conducting fieldwork along the
river might raise ethical issues.
Analysing and Interpreting
Distribution Data
Specification Link
• Analyse and interpret data relating to
the distribution of organisms,
recognising correlations and causal
relationships
• Appreciate the tentative nature of
conclusions that may be drawn from
such data.
Task
Answer the questions on page 20 in the
text book.
Human Populations
• Population size and structure, population growth
rate, age-population pyramids, survival rates
and life expectancy.
Candidates should be able to:
• interpret growth curves, survival curves and
age-population pyramids
• calculate population growth rates from data on
birth rate and death rate.
• relate changes in the size and structure of
human populations to different stages in
demographic transition.
Overall Trends
Why?
• For most of history – kept in check by
food availability, disease, predators and
climate.
• Recent history – population explosion
due to the agricultural revolution,
industrial revolution and development of
medicine.
Factors which now affect human
population
•
•
•
•
Birth rate
Death rate
Immigration
Emigration
Key Terms
The birth rate is the number of live
births each year for every 1000 people
in the population.
A death rate is the number of people that
die each year for every 1000 people in
the population.
Equations
• Pop growth = (births + immigrations) –
(deaths + emigration).
• You may not get the immigration or
emigration numbers, therefore just
minus birth rate by death rate.
Factors affecting birth rates
• Economic conditions
• Cultural and religious backgrounds
• Social pressures and conditions
• Birth control
• Political factors
Birth rate = no births per year
total pop. In the same year
x1000
Factors affecting Death rates
Age profile
Life expectancy at birth
Food supply
Safe drinking water and effective
sanitation
• Medical care
• Natural disasters
• War
•
•
•
•
Equation
death rate = no deaths per year
x1000
total pop. In the same year
Learning Check
• calculate population growth rates from
data on birth rate and death rate.
• interpret growth curves, survival
curves and age-population pyramids
• relate changes in the size and structure
of human populations to different
stages in demographic transition.
Tasks
Read through notes on demographic
transition model, survival curves and
population pyramids.
Attempt questions in booklet.
Make note of any patterns in types of
questions.
Highlight any misconceptions
Independent Study
• Complete all the questions in booklet.
• Bring your weekly revision plan, all unit 4
notes (Inheritance and Selection,
Ecosystems and populations).
• Revise for ecosystems and populations
test.