Lecture 6 dynamics of the human population

1. Lecture content
• Population and Environment
– Exponential Growth Review
– Logistic Growth Curve
– Replacement Level Fertility
– Forecasting Population Change
– Age Structure
– Human Population’s Effects on the Earth
– Group exercise rules and topic allocation
Lec 6; MrL 1

2. Exponential Growth
An exponentially growing
population theoretically
increases forever.
Exponential growth rate: the annual growth
rate is a constant percentage of the
population
Lec 6; MrL 2

3. Human Population as a Logistic
Growth Curve
• On Earth, which is limited in size,
exponential growth is not possible, as
Thomas Henry Malthus pointed out in
the 18th century.
• If a population cannot increase
forever, what changes in the
population can we expect over time?
• S-shaped curve known as the Logistic
Growth Curve.
Thomas Henry Malthus
Lec 6; MrL 3

4. Logistic Growth Curve
• A logistic population would
increase exponentially only
temporarily. After that, the
rate of growth would
gradually decline until an
upper population limit is
reached.
• The upper population limit is
called the logistic carrying
capacity.
• Once that had been reached,
the population would
remain at that number.
Lec 6; MrL 4
This was first suggested in 1838 by P. F.
Verhulst

5. Exponential
growth
curve
Logistic
growth
curve
Lec 6; MrL 5

6. Replacement level fertility
• Replacement fertility is the total fertility rate
at which women would have only enough
children to replace themselves and their
partner.
• The replacement fertility rate is roughly 2.1
births per woman for most industrialized
countries.
Lec 6; MrL 6

7. World population, 1950-2150: three
possible features
Between these
three population
features which one
do you think is
going to happen?Lec 6; MrL 7

8. Forecasting Population Change
• Populations change in size through births, deaths, immigration
(arrivals), and emigration (departures).
• Population change in terms of actual numbers in a population:
P2 = P1 + (B - D) + (I - E)
o P1 is the number of individuals in a population at time 1 (e.g.,
1000),
o P2 is the number of individuals in that population at some later
time 2 (?)
o B is the number of births in the period from time 1 to time 2 (e.g.,
700),
o D is the number of deaths from time 1 to time 2 (e.g., 200),
o I is the number entering as immigrants (e.g., 600), and
o E is the number leaving as emigrants (e.g., 100).
= 2000
Lec 6; MrL 8

9. Age Structure
• Population age structure is the proportion of the
population of each age group.
Lec 6; MrL 9
• The age structure of a population affects
birth rates, death rates, and growth rates;
has an impact on the environment; and has
implications for current and future social
and economic conditions.

10. Declining growth
Slow growth
Rapid growth
Bangladesh
Rapid growth
Lec 6; MrL 10

11. Human Population’s Effects on Earth
• When there were few people on Earth and limited
technology human impacts on environment was local
but not necessarily less. Human has impacts on
environment for a surprisingly long time such as use of
fire to clear land.
• The problem now is that there are so many people and
our technologies are so powerful that our effects on
the environment are even more global and significant.
This could cause a negative feedback—the more
people, the worse the environment; the worse the
environment, the fewer people.
Early stage vs modern stage
Lec 6; MrL 11

12. • Modern technology increases the use of resources and
enables us to affect the environment in many new ways,
• For example, before the invention of chlorofluorocarbons
(CFCs), which are used in spray cans and in refrigerators and
air conditioners, we were not causing depletion of the ozone
layer in the upper atmosphere.
• Similarly, before we started driving automobiles, there was
much less demand for steel, little demand for oil, and much
less air pollution.
• Others
The Human Population’s Effects on the Earth
Lec 6; MrL 12

13. The Human Population’s Effects on the Earth
The danger that the human population poses to the
environment is the result of two factors: the number of people
and the environmental impact of each person.
Total impact (T) of the human population on the environment:
• T = P × I
P is the population size, and
I is the average environmental impact per person
• The impact per person varies widely, within the same nation
and also among nations.
Lec 6; MrL 13

14. • The average impact of a person who lives in high technology
country is much greater than the impact of a person who
lives in a low-technology society.
E.g., CO2 emissions in 2010 (tons/capita): Bangladesh - 0.4;
USA - 17.6, Norway – 11.7
• But even in a low-technology nation the higher number of
people leads to large-scale environmental effects.
E.g., Population (in 2014): Bangladesh - 157,058,000; Norway – 5,090000
Total CO2 emissions: Bangladesh– 157m × 0.4= 62.8mT (low-technology)
Norway– 5.09m × 11.7 = 59.55mT (high technology)
• What will happen if high technology country plus higher
number of population?
USA – 318 m×17.6=5596.8mT
Lec 6; MrL 14

15. References for today’s lecture
• BOTKIN, D. B. & KELLER, E.A. 2011.
ENVIRONMENTAL SCIENCE: EARTH AS A
LIVING PLANET. JOHN WILEY & SONS, INC.
• Some figures are from internet
• If you find anything in the slides but NOT in
Botkin and Keller, then read directly from the
slides. E.g., some examples of slide 13.
15Lec 6; MrL

16. Lec 6; MrL 16
• Group exercise rules and topic allocation

17. Group exercise (20 marks)
Lec 6; MrL
17
Group name Topics
G1 Green economy and Bangladesh
G2 Natural environmental hazards in Bangladesh
G3 Deforestation in Bangladesh
G4 Global warming and Bangladesh
G5 Electronic waste
G6 Environmental effects of industry in Bangladesh
G7 Sustainable Development Goals (SDGs)

18. Instructions
Lec 6; MrL
18
 The group exercise will have two parts: report and
presentation
 A. Report (10 marks)
 Group work is needed.
 Each would contribute equally.
 The report would have at least 5 sections.
 Each student will present at least one section in which he/she
contributed more.
 For writing the report follow any standard format can be followed
such as
http://education.exeter.ac.uk/dll/studyskills/assignment_presentati
on.htm

19. Instructions
Lec 6; MrL
19
 Total length of the report would be 3,000- 4,000
words;
 1st page will have the exercise title, students’ names,
IDs and part of the report prepared by him/her, date
of submission, and course details;
 2nd page would contain table of contents;
 report writing would start after that.

20. Presentation
Lec 6; MrL
20
 Presentation (10 marks) (4 mins for each);
Assessment criteria Marks allocated (10)
Content (quality and quantity) 4
Fluency/style 3
Quality of slides 2
Timing 1

21. Lec 6; MrL
21
 Deadline of report/assignment submission is
22 October for all groups
 Presentation will be on the following week.
 Both hard and soft copies (in my email containing file
name: section_Group number_title) need to be
submitted.

22. Selection of group members and topic
Lec 6; MrL
22
 You select 5 members and a topic by yourself and
give me in the next class.
 In a page write group name, assignment title,
students/members name and IDs

23. Group exercise: roundtable meeting by each group
• Objectives:
• know each other
• explore research
topic more
• Making a table of
contents for the
report/assignment
• Length (words) of
each sub-section
in the report
Lec 6; MrL 23
Topic Length Who is contributing?
1.
Introducti
on
150 words Anika
2. 500 Anika
3. 500 Zahir
4. 600 Faiz
5. 700 Zia
6. 400 Farzana
7.
Conclusion
200 Farzana
Table of contents

24. Any question?
24Lec 6; MrL