1. Population
Ecology and
Human Impact
By : Mmatsela Kobe

2. - Is the study of interactions among
organisms and their environment

3. Population Dynamics
Population:
All the individuals of a species that
live together in an area
Demography:
The statistical study of populations,
allows predictions to be made about
how a population will change

4. Population Dynamics
Key Features of Populations

5. Population size
… is the number of individuals present at a given time.
The passenger pigeon was once
North America’s most numerous
bird, but it is now extinct.

6. Population density
… is the number of individuals per unit area.
In the 19th century, the flocks of passenger pigeons showed high
population density.

7. Population distribution
…is the spatial arrangement of individuals.



Random- No patterns
Uniform- Interactions among individuals
Clumped- Often correlates with resources

8. Population
Distribution

9. Changes in a Population
•
factors determine population changes
1.births
2.deaths
3.migration
• immigration
• emigration

10. How Do You Affect Density?
 Immigration: movement of individuals into a
population
 Emigration: movement of individuals out of a
population
 Density-dependent factors: Biotic factors in the
environment that have an increasing effect as
population size increases (disease, competition,
parasites)
 Density-independent factors: Abiotic factors in the
environment that affect populations regardless of
their density (temperature, weather)

11. How Are Populations Measured?
• Population density = number of individuals in a given area or
volume
• Count all the individuals in a population
• Estimate by sampling
• Mark-Recapture Method

12. Formula for capture-recapture method
Marked animals in 2nd sample
Total caught in 2nd sample
=
Marked animals in 1st sample
Total population size

13. How Do Populations Grow?
Idealized models describe two kinds of population growth:
1. Exponential Growth has no upper limit and populations grow very quickly
2. Logistic Growth has a limit and growth approaches this limit in a sigmoidal fashion
Logistic growth is more realistic in real life, but exponential growth is a better model
for bacterial cultures, etc. that have unlimited resources and space

14. Exponential Growth
• Also known as a J-curve
• Growth is a fixed percentage of the whole
(e.g., 10% per day or year)
• Population is growing at its full biotic
potential

15. Exponential Growth Curve
• A J-shaped growth curve, described by the
equation G = rN, is typical of exponential
growth
– G = the population growth rate
– r = the intrinsic rate of increase, or growth
rate in an ideal environment (births-deaths)
– N = the population size

16. Logistic Growth
• Also known as S-curve
• Growth slows as the population
approaches Carrying Capacity
• Populations stabilize at carrying capacity

17. Logistic Growth Curve
– K = carrying capacity
– The term
(K - N)/K
accounts
for the
leveling
off of the
curve

18. Carrying Capacity
• Carrying Capacity (k):
• The maximum population size that can be
supported by the available resources
• There can only be as many organisms as the
environmental resources can support

19. Survivorship
• three types of survivorship curves
• late loss (Type I)
• have a high survival rate of the young, live out most of their expected life span and die
in old age.
• constant loss (Type II)
• relatively constant death rate throughout their life span - death could be due to hunting
or diseases.
• early loss (Type III)
• have many young, most of which die very early in their life.

21. Factors Limiting Growth Rate
• Declining birth rate or increasing death rate are caused
by several factors including:
• Limited food supply
• The buildup of toxic wastes
• Increased disease
• Predation

22. Reproductive Strategies
r Selection (many
offspring)






Short life span
Small body size
Reproduce quickly
Have many young
Little parental care
Ex: cockroaches,
weeds, bacteria

23. Reproductive Strategies
 K Selection (few
offspring)
 Long life span
 Large body size
 Reproduce
slowly
 Have few young
 Provides
parental care
 Ex: humans,
elephants

24. Age Distribution
• Distribution of males and females in each age group of a population
• Used to predict future population growth

25. Human Population Growth
• J curve growth
• Why doesn’t environmental resistance take effect?
• Altering their environment
• Technological advances
• The cultural revolution
• The agricultural revolution
• The industrial-medical revolution

26. Communities in Transition
• Ecological succession: process by which organisms occupy a site and
gradually change environmental conditions by creating soil, shelter,
and increasing humidity.
• Primary succession: community begins to develop on a site previously
unoccupied by living organisms.
• Secondary succession: existing community is disrupted and a new one
develops.

28. The Human population
•World population increases every year.
•Increased population=increased needs.
•Uncontrolled population growth=problems in the avaibility of
resources needed by people.
•Increase environmental damage.
•Therefore, some effort to control the population growth should be
put into action in order to minimize the problems that may occur.

29. The Human Population
Doubled three times in the last three centuries
About 6,1 billion and may reach 9.3 billion by the year 2050
Improved health and technology have lowered death rates

30. Human Impacts on Ecosystems
Habitat degradation and fragmentation
Ecosystem simplification
Genetic resistance
Predator elimination
Introduction of non-native species
Overharvesting renewable resources
Interference with ecological systems

31. References
• This presentation is a mash up of 5 presentations by the following:
 Choudhury, S.M.(2009). Population Ecology.
http://www.slideshare.net/Shohail/population-ecology-1968004?qid=d37f2617-c106-4648-847b-08e9a5820e9b&v=default&b=&from_s
(Accessed on 06/03/2014).
 Pointer, K. (2011).Population ecology : Populations.
http://www.slideshare.net/coachpointer/population-ecology-9976847?qid=d37f2617-c106-4648-847b-08e9a5820e9b&v=default&b=&fr
(Accessed on 06/03/2014)
 Tnewberry. (2008). Population ecology. http://www.slideshare.net/tnewberry/population-ecology-514438?qid=d37f2617c106-4648-847b-08e9a5820e9b&v=default&b=&from_search=3.( Accessed on 06/03/2014)
 Bombon, R. (2008). Population ecology. http://www.slideshare.net/gobuktaragang/population-ecology?qid=2c884cb11ff2-41dd-90c8-f87a735d8bb9&v=qf1&b=&from_search=28. (Accessed on 05/03/2014).
 Kesturi, A. (2013). Human population and its impact. http://www.slideshare.net/alfikesturi/7-7-human-population-and-itsimpacts?qid=f2191318-2cf8-4777-bac7-6e29c191e56b&v=qf1&b=&from_search=1. (Accessed on 05/03/2014)