1. Populations and Population Growth

2. Populations
Population - a group of interbreeding organisms of the same species that live together at the same time in the same place

3. Population size - number of members in a population
2 ways to estimate population size:
Random sampling – used mainly for plants; samples and counts organisms in random plots
Mark & recapture – used mainly for animals; captures, marks, and releases animals, then samples the population again

4. Population growth – an increase in the size of a population
2 kinds of population growth:
Exponential
Logistic
Why do populations grow???

5. Population Growth Exponential – “J” curve
- population growth is slow at first then increases rapidly
- more members = more reproduction
- continues as long as there are unlimited resources

6. Why is exponential unrealistic?
Resources (food, space, etc.) are limited in nature!
There are other limiting factors.
Things that limits the survival of an organism
Ex. Predators, diseases, natural disasters

7. Populations cannot grow indefinitely.
They will reach their carrying capacity
The maximum number of individuals in a population that an area can support

8. Population Growth Logistic – “S” curve
Shows a population growing with limits such as food and space
Levels off at carrying capacity
Carrying capacity can be raised or lowered depending on the amount of available resources

9. Even more realistic…

10. Human Population Growth

11. Human Population Graph

12. Human Population Human population remained stable for many years
Human population has grown exponentially since the time of the industrial revolution
Humans have not reached their carrying capacity yet because we can:
Plant/raise food
Build for shelter
Control/treat diseases

13. Growth Rate Growth Rate = Birth – death
Birth rate - # of births per year
Factors affecting birth rate: religious/social beliefs, use of birth controls
Death rate - # of deaths per year
Factors affecting death rate: diseases/medicines, nutrition, homicides

14. If birth rate is greater than death rate…
Population increases
If birth rate is less than death rate...
Population decreases

15. Age Structure
Distribution of various age groups in an area