Life Sciences Gade 11 Term 3 Week 7_2020 (1).pdf

Life sciences weekly lesson plan for Population ecology. Life Sciences. Grade 11. I has activities and notes that will help the teacher to easily navigate around the topic population ecology in grade 11 life sciences. It is aligned with the standard of caps curriculum. it also has activities to help with checking if the objectives and learning requirements have been met.

1. Directorate: Curriculum FET





SUBJECT and GRADE Life Sciences Grade 11
TERM 3 Week 7
TOPIC Population ecology
AIMS OF LESSON At the end of this lesson you should be able to know and understand the following:
• Population size: Immigration, emigration, mortality, natality; fluctuations and limiting factors, logistic and
geometric growth curves with phases
• Interactions in the environment: predation, competition, specialisation, parasitism, mutualism, commensalism
RESOURCES

Paper based resources
Refer to your textbook section on:
• Population size and
• Interactions in the environment
INTRODUCTION

Refer to the following sections for background information:
• the microorganisms in Grade 11
• environmental studies in Grade 10
CONCEPTS AND SKILLS

Below are definitions of some of the terms that you will study under this section. Use your textbook and underline all
the new terms/words that you encounter while studying through this section. Use the glossary in your textbook to
define these new terms/words (Note: At least 2 marks are awarded if you can define a term correctly in a test or
examination)

Population - a group of organisms of the same species that can interbreed to produce fertile offspring and occupy a given
area at a certain time
Species - a group of organisms with similar characteristics that are able to interbreed to produce fertile offspring
Population size – total number of individuals in a population
Population density – number of individuals of a population per unit area e.g. 10 sheep per hectare
Natality - The inherent ability of a population to increase in size
Immigration – the one-way movement of organisms into an area where they become established
Emigration – the one – way movement of organisms out of an area

2. Culling- The selective killing of wild animals when their numbers exceed the carrying capacity of an environment
Mutualism - The relationship between different species in which both benefit from the association
Study the following content:
1. Population size:
The following FOUR factors (parameters) have an effect on population size i.e.
• Natality – birth rate of a population. Natality causes an increase in population size.
• Mortality – death rate of a population. Mortality causes a decrease in population size
• Immigration - the one-way movement of organisms into an area where they become established. Immigration
causes an increase in population size
• Emigration - the one – way movement of organisms out of an area. Emigration causes a decrease in population size.

2. Determining population size:
2.1 Direct techniques:
• Total count of all individuals in the population e.g. census of human population, counting of large animals and aerial
photographs of groups of animals.

2.2 Indirect techniques:
• Counting of only a part of the population e.g. mark-recapture technique and quadrat technique.

2.2.1 Mark -recapture technique

• A number of individuals are caught, counted and marked (1
st
sample)
• Marked individuals are released in the environment and given sufficient time to mix with the rest of the population
• Another group of individuals is caught and counted and they are known as the 2
nd
sample
• The number of marked individuals in the 2
nd
sample are counted
• Determine the estimated size of the population using the following formula:
??????=
?????? ?????? �
�


➢ P = estimated population size
➢ M = total number of individuals captured and marked in 1
st
sample
➢ S = total number of individuals captured in 2
nd
sample
➢ T = number of marked individuals in 2
nd
sample

3. 2.2.2 Quadrat method:

• An area where organisms must be counted is demarcated and the surface area is determined.
• A quadrat (e.g. square frame of known size e.g. 1m
2
) is placed on the ground and the organisms in the quadrat are
counted
• The process is repeated a few times randomly in different areas of the demarcated area.
• The following formula is used to determine the number of organisms:

Population size = average number of individuals per quadrat X
surface area of the area
surface area of the quadrat


2.3 Population growth forms
2.3.1 Geometric (J-shaped) growth form

• Initially the increase in population size is slow as there are a few individuals
• The population size then increases rapidly because of optimum environmental conditions.
• As environmental conditions become unfavourable (environmental resistance becomes effective) e.g. a shortage of
food, oxygen etc. the increase suddenly comes to an end.

Please note: Certain factors prevent unlimited growth in a population. These factors are known as limiting factors e.g.
shortage of food, water, living space, shelter, diseases. Together these factors are called environmental resistance.

4. 2.3.2 Logistic (S-shaped) growth form:



• Lag phase: Population growth is slow because the population takes time to acclimatise, to become sexually mature,
seek partners for mating and to produce new offspring.
• Accelerating /geometric/exponential growth phase: The population grows rapidly and reaches its maximum
growth rate because there is little or no environmental resistance. Natality is higher than mortality.
• Decelerating growth phase: Growth rate steadily decreases because of an increase in environmental resistance.
• Equilibrium/stationary phase: The population numbers reach the carrying capacity (the maximum number of
individuals that a specific environment can support) of the environment and stabilize around this value. Natality is
more or less equal to mortality.

2.4 Regulation of population size:

• Once a population reaches its maximum size the numbers will not remain constant. The numbers will fluctuate due
to changes in environmental resistance.
• The size of a population may fluctuate seasonally or annually depending on environmental factors and available
resources.
• The limiting factors play an important role in the regulation of population size. These are the factors that increase or
take effect when the population numbers increase and are also called the density dependent factors. Density
dependent factors are therefore factors that take effect when population size or density increases. Density

5. dependent factors include food supply, living space, disease, shelter etc. An increase in population size results in a
greater demand for food, water, living space, shelter etc.
• Density independent factors e.g. extreme changes in temperature, droughts, floods, earthquakes etc. are factors
that regulate population size regardless of the size or density of the population. These factors result in a drastic
decline in population numbers.

3. Interactions in the environment:

3.1 Predation:
• Feeding interaction where one organism, the predator (e.g. lion), hunts, kills and eats another organism, the prey
(e.g. zebra).
• Predation helps to control the size of populations.
• The higher the prey numbers, the more predation will occur.
• The lower the prey numbers, the fewer predators will survive due to a shortage of food.

Graph showing predator-prey relationship


3.2 Competition:
• Competition takes place when two or more individuals compete for the same limited resources e.g. food, water,
mating partners etc.
• Intraspecific competition takes place between individuals of the same species e.g. male lions competing for a
female
• Interspecific competition takes place between individuals of different species e.g. hyenas and vultures competing
for the same food source.

6. 3.3 Competitive exclusion:

• Two different species that need the same limited resources cannot occupy the same niche in the same habitat over
a long period.
• The one species will outcompete the other which will result in the emigration or extinction of the other species.
• This is known as the principle of competitive exclusion.

3.4 Resource partitioning:

• Two species can co-exist in one habitat but use the same resources differently e.g. one species feeds during the day
and the other at night, two species feeding on different heights of the same tree etc.

3.5 Mutualism:

• A symbiotic relationship between two organisms of different species where both benefit e.g. bees getting food
from a flower and the flower is cross-pollinated.

3.6 Commensalism:

• A symbiotic relationship between two organisms of different species where the one benefits and the other neither
benefits nor is harmed e.g. the suckerfish on sharks that feeds on the leftover food and the suckerfish also gets
protection.

3.7 Parasitism:

• A symbiotic relationship between two organisms of different species where one benefits (parasite) and the other is
harmed (host) e.g. ectoparasites like lice, fleas and endoparasites like the tapeworm.

Know the meaning of instructional verbs in test and examination questions e.g.
Instructional verb Meaning
Name Give the name of something
Differentiate Use differences to qualify between two or more categories
Tabulate Draw a table and indicate the answers as direct pairs.
Describe State in sentences the main points of a process
Explain Give your answer in a cause-effect or statement and reason sequence

7. Answer the following questions:
Question 1
1. GRAPH A below represents the number of bacteria in a growth culture over a period of time. GRAPH B shows changes in
the human population size over a period of time. (Grade 11 DBE Exemplar 2013)


1.1 Use GRAPH A to answer the following questions.
1.1.1 During which period (A, B or C) did natality exceed mortality for many hours?
1.1.2 Explain the pattern of growth during Period B.

1.2 Use GRAPH B to answer the following questions.
1.2.1 State in what way the growth of the human population is similar to that of the bacterial population?
1.2.2 Explain why it may take the human population longer to reach the type of growth shown by the bacteria population in
Period B.
1.2.3 State TWO precautionary measures which may be implemented in South Africa to slow down the growth in the human
population.

8. Question 2:
2. Read the following passage and then answer the questions that follow. (Free State P1 Nov 2016)
In 1990 the estimated impala population in a certain environment was approximately 8 000. Large
populations of lions and cheetahs were also present. Between 1990 and 2000 about half the sizes
of the populations of lions and cheetahs were eliminated. By 2002 the number of impala
increased to about 80 000 and nearly all the grass, shrubs and young trees had been eaten.
During the winter, 80% of the impala population was wiped out and this decline continued until
only 4 000 impalas were left. The vegetation, however, continued to degenerate for a long time.
In the beginning it was estimated that the carrying capacity of the area was only 20 000 impalas.

2.1 Differentiate between the terms “prey” and “predator”.
2.2 By referring to the passage, give the names of organisms that are involved in the following:
(a) Intraspecific competition
(b) Interspecific competition
2.3 State why the impala continued to decline after 80% had died during the winter?
2.4 State what is meant by each of the following in a population:
(a) Carrying capacity
(b) Species
2.5 Is predation a density-dependent or a density-independent factor? Give a reason for your answer.


Question 3:
3. Two sea-birds, Phalacrocorax aristotelis (commonly known as the shag) and Phalacrocorax canbo (commonly known as
the cormorant), feed in the same area and build their nests on the same mountain cliffs. (Life Sciences NSC P2 Nov 2013)

The table below shows the percentages of different prey eaten by each of these types of birds.

9. 3.1 Explain why the shags and the cormorants are not in direct competition with each other, although they feed in the same
area.
3.2 Name the phenomenon explained in QUESTION 3.1.
3.3 State ONE resource mentioned above for which the two species compete with each other.
3.4 Name the type of competition that occurs between the two species for the resource mentioned in QUESTION 3.3


Question 4:
4. The table below illustrates the data collected during an investigation to determine the changes in the population size of
impala in a nature reserve. (Life Sciences NSC P2 Nov 2012 Version 1)

4.1 Use the data in the table to draw a line graph to show the population growth form of the impala over the 10-year
period.
4.2 State the type of growth form that is illustrated by the graph?
4.3 Describe ONE characteristic of the growth form named in QUESTION 4.2.
4.4 Name the phase from 2000 to 2002 illustrated in the graph.
4.5 Explain the pattern of growth in the phase mentioned in QUESTION 4.4.
4.6 An eland population was introduced into the same nature reserve in the year 2000. The eland and impala feed on the
leaves of the same trees. An adult impala is smaller and shorter than an adult eland.
(a) Explain why the impala and the eland are not in competition with each other, although they feed on the same food
source.
(b) Name the interaction explained in QUESTION 4.6(a).

10. Question 5:
5. Study the following graph which represents the population of rabbits and wild dogs in a specific habitat. (Grade 11 Life
Sciences NSC P2 2007)




5.1 State the relationship shown in the graph.
5.2 Explain how the above relationship acts as a density-dependent factor in regulating the population size of the rabbits
and the wild dogs.
5.3 State what is represented by line A.
5.4 Explain what will happen to population B when its size reaches that indicated by line A.
5.5 State which line (B or C) would represent the rabbit population?

11. Common errors made by learners in examinations:
• Do not understand instructional verb/s in a question e.g. the difference between describe and explain.
• Not able to interpret information in texts and graphs
• Not able to know the terminology in this section
ACTIVITIES/
ASSESSMENT
• Complete the activities/questions on this section in your textbook.
CONSOLIDATION • Define all the terminology relevant to the topic/s covered in this lesson
Note: The knowledge and skills gained in this section will help you to have a better understanding of the following section
that you still need to deal with
• Human population
VALUES By studying and learning about population ecology you will understand the need for using scientific knowledge responsibly
in the interest of society and the environment.