1. Populations
Biology

2. http://www.worldometers.inf o/world-population/
Populations
Objective: to understand the way that populations of different organisms grow and shrink, and what factors cause these changes in a population
o/world-population/

3. I. Describing a population
Geographic Distribution: the area inhabited by a population
Map shows the Geographic Distribution of the California Quail

4. 2. Population density: number of individuals per unit area

5. few individuals in a unit area: example: trees High density:
Population Density:
b. Low density:
few individuals in a unit area: example: trees
High density:
lots of individuals in one area: example grass

6. 3. Growth rate: how quickly a population changes in size
Example: Some bacteria can double their population in minutes! 
45 Minutes

7. 3. Growth rate: how quickly a population changes in size
Example 2: Trees can not double their population in 45 minutes. Its takes years and years for a population of trees to double in size. 
45 years

8. II. Factors affecting population growth
Birth rate
Death rate

9. Birth = Death 
Stays the same
100 Born Die

10. b. Birth > Death 
Increases
150 Born Die

11. Birth < Death 
Decreases
50 Born Die

12. 3. Immigration: movement of individuals into an area
Example:
The Bison immigrates to a meadow full of grass because it provides a good source of food.

13. 4. Emigration: movement of individuals out of an area
Example:
The Bison Emigrates away from a meadow without grass because it does not provide a good source of food.

14. 5. You must emigrate from somewhere in order to immigrate to somewhere.
Emigrate from..
Immigrate to..

15. Exponential Growth: individuals reproduce at a constant rate
III. Types of Growth
Exponential Growth: individuals reproduce at a constant rate
Conditions necessary for exponential growth
Example:
Shape of graph
Graph
1. Unlimited Resources
2. Absence of disease and parasites
Bacteria J

16. Exponential Graph

17. 2. Logistic Growth: Population grows rapidly until some factor limits growth
When does population growth slow or stop?
Birthrate: Death rate:
Immigration: Emigration:
b. Example:
c. Shape of Graph
d. Graph
Down Up
Down Up
Most animal populations in nature S

18. Logistic Graph

19. e. Carrying capacity: Maximum # of individuals that an area can support

20. IV. Limits to Growth
Limiting Factor: Condition that controls population size ex: food, land
Animals in a population may not have enough food to go around

21. IV. Limits to Growth example: Effect on evolution:
2. Competition: Two or more species attempt to use same resource
example:
Effect on evolution:
Bird and squirrel both eat berry

22. b. Effect on evolution:
both species under pressure to change in ways that decrease their competition
Squirrel eat nuts
Bird eat worm

23. 3. Predation: one organism eats another
a. example: Mouse and Snake b. predator: Hunter c. prey: Hunted

24. 3. Predation: one organism eats another
d. Effect on evolution: prey species evolve defenses against predators, predators evolve counter defenses
Snake: forked tongue and heat vision
Mouse: Camouflage

25. 4. Parasitism: organisms live and feed inside/on a host organism
examples: Fleas, ticks, leaches, tape worm

26. 5. Random events: Unusual weather, human activities, natural disasters.