1. POPULATION BIOLOGY

2. Principles of Population Growth
Increase in size of a population over time.
Bacteria/yeast may be plated on agar in a petri dish and the colonies counted over time.
Plants or animals may be introduced into a new environment with plentiful resources and their growth observed.

3. How fast do populations grow?
Population growth is never linear.
Carrying Capacity
Number of organisms
S shaped curve
J shaped – exponential increase overtime where there is unlimited resources
S shaped - limited resources – level carrying capacity – supported by the environment
TIME

4. POPULATION GROWTH
*resources – light predators

5. Limits of the environment
Limiting factors such as food, space and water control the size of a population.
“Leveling off” of population results in S- shaped growth curve.
CARRYING CAPACITY (K) is the number of organisms that can be supported in an environment.
Population below K births exceed deaths
Population above K deaths exceed births

6. Patterns of population growth
Rapid life history pattern organisms in an unpredictable environment.
Mosquito: small body size, mature quickly, reproduce early, short life span. Population fluctuate rapidly depending upon conditions.
Long life history pattern organisms living in stable environments.
Elephants: large, mature and reproduce slowly, longer life span. Population size near carrying capacity
Which one do we fit into? We are growing exponentially – technology, med, food supply

7. Environmental limits to growth population
DENSITY - DEPENDENT FACTORS
Effect increases as population increases
Disease, competition, parasites, food
DENSITY - INDEPENDENT FACTORS
Affects all population regardless of size
Temperature, floods, habitat destruction, drought

8. Organism Interactions Limit Population Size
Predation
Predator-prey relationship cycles:
Ex: lynx and rabbits
Effects of competition
Population low, resources are plentiful, no problems, as population increases resources become limited and competition increases.
Effects of crowding and stress
Overcrowding leads to stress. Individuals become more aggressive, show less parental care, decreased fertility

10. HUMAN POPULATION GROWTH
1400 pop black plague -
Disease

11. Demographic trends
Demography: study of human population growth characteristics.
Demographers study population growth rate, age structure and geographical distribution.
Human population has increased exponentially
Humans are able to reduce environmental effects.

12. Effects of birthrates and death rates
Slow population growth rate if deaths, exceed births Fast population growth rate if births exceed deaths

13. Does age affect population growth?
A population with more young than old people will grow faster than the reverse.
Age structure is shown on graphs and helps predict growth rate of population
Broader base has faster population that is increasing

14. AGE STRUCTURE GRAPHS

15. Mobility has an effect on population size
Immigration: movement of individuals into an area.
Emigration: movement of individuals out of a population
International migration does not affect world population
National and local populations are affected by internal migrations