1. Honors Biology – Chapter 5
Populations
Honors Biology – Chapter 5

2. What is a Population?
A group of the same species living in a given area
It is populations of organisms that interact in ecosystems
Example:

3. An Introduction – Sea Otters of the Pacific Northwest
Life in kelp forest community

4. An Introduction – Sea Otters of the Pacific Northwest
Sea urchins as food
Sea urchins eat kelp
Sea otters nearly eliminated due to hunting
Sea urchin populations rise
Kelp forests decline
Restoring balance: Sea otters declared endangered – protected from hunting

5. Predator/Prey Population Relationships
Hare / Lynx
Hare population goes up
Lynx population goes up
Lots of food (hares) available
Causes hare population to go down
More lynx = more predation on hares
Causes lynx population to go down
Hare population decrease means less food for lynx and they die

6. Hare/Lynx

7. 4 Characteristics of Populations
Geographic distribution
Range
Area inhabited by a population
Density
Number of individuals per unit area
Growth rate
Age structure

8. Population Growth 3 factors affect population size Number of births
natality
Number of deaths
mortality
Number of individuals that enter or leave a population
Immigration - enter
Emigration - leave

9. Population Growth
A population will increase or decrease in size depending on how many individuals are added to it or removed from it
Growth occurs if
More individuals are born than die
If birth rate equals death rate the population will stay near the same size

10. Movement into or out of a population
May be caused by
Young animals mature and leave the area
Shortage of food in an area

11. Exponential Growth
Individuals in a population reproduce at a constant rate
Initially, growth is slow
Overtime the population becomes larger and large until it approaches an infinitely large size
Ideal conditions with unlimited resources required

12. Bacteria Fastest rates of reproduction among living things
20 minutes for population to double
Why don’t they take over the Earth?
NOT unlimited resources

14. Logistic Growth
Growth pattern that occurs when a population’s growth slows or stops following a period of exponential growth.
Things that slow a population’s growth
Natality (birth rate) decreases
Mortality (death rate) increases
Rate of immigration decreases
Rate of emigration increases

15. Logistic Growth
Also, when birth and death rates are the same, the population growth will slow or even stop for a time
Even when a population stops “growing”, the population is still rising and falling somewhat – though the ups and downs average out to the same population size.

16. Logistic Growth Curve Slow growth Exponential growth Growth levels off
Carrying Capacity K
Dotted line
The maximum number of individuals that an environment can support

17. Limits to Growth Limiting Factors
Factors that cause population growth to decrease
Competition
Predation
Parasitism
Drought
Human disturbance

18. There are TWO types of limiting factors
Density Dependent
Density Independent

19. Density Dependent Limiting Factors
Depends on the size of a population
Usually greatest impact when the population is large and dense
Include
Competition
Predation
Parasitism
Disease

20. Density Independent Limiting Factors
Affects all populations (large or small) in similar ways.
Unusual weather
Natural disasters
Human activities
Like Habitat Destruction

21. Human Population Growth
Like other populations of organisms, the human population tends to increase with time.

22. Human Population Growth Curve
Initially slow
Food scarce
Life harsh
500 years ago
More rapid growth
Currently EXPONENTIAL
Why?
Agriculture and industry advances
Food supply increased
Improved sanitation
Medicine

23. Human Population Growth Curve

24. Demography The study of human populations
Examines human populations and tries to predict how they will change over time.

25. Demographic Transition
Population growth in some countries has slowed
U.S.
Japan
Much of Europe
Why?
Hypothesis: These countries have completed the “demographic transition

26. Demographic Transition
A dramatic change in birth and death rates
What happens
Initially both birth and death rates high
Advances in nutrition, etc. lower death rate
Population increases rapidly
Societies modernize – increase education, etc.
Families have fewer children
Birthrate falls to meet the death rate
Population growth stops

27. Populations that have NOT completed the demographic transition
Most countries
India
China

28. Age Structure Diagrams
Shows how many people of different ages and genders are in a population
Useful in predicting future population growth

29. Age Structure Diagram

30. Predicting Future Population Growth
Factors to consider
Age structure of each country
Prevalence of life-threatening diseases
Predictions for 2050
9 billion people on Earth

31. Effects of Human Population Growth
Some scientists suggest if human population growth rate does not become LESS than 0 (deaths outnumber births)
Serious damage to environment
Serious damage to global economy
Some economists say that technology advances and changes in societies can control negative impacts