1. 5.1 Populations I. What is a population?
A. Def- made up of a group of organisms (same species) that live together in one place at one time & interbreed.
1. Can be large or small
B. Important because populations of different species interact & affect one another
1. including human populations

2. II. Population Growth
A. Factors that affect growth
1. Births
2. Deaths
3. Immigration
a. movement of individuals into a population
4. Emigration
a. movement of individuals out of a population

3. B. Exponential Growth
1. More births than deaths
2. Causes a J-shaped curve when graphed
3. Numbers increase by a certain factor in each successive time period
4. Starts slowly when small population
5. Increases speed as population gets larger
a. ex- bacteria
1. 1 bacteria, copies itself every min.=10 million bacteria in 10 hrs.

5. C. Logistic Growth
1. Populations do not grow unchecked forever
2. S-shaped curve when graphed
3. Limiting factors
a. food availability, predators, & disease
4. Ecosystems can only support so many organisms
a. Carrying capacity
1. the largest population an environment can support
5. Eventually birth rate = death rate, which = no more growth

7. 6. Density-dependent factors
a. variable affected by number of organisms present in an area
1. not enough nesting sites for birds = less birds born
7. Density-independent factors
a. affect a population regardless of population density
1. weather, fire, floods

8. III. Factors that affect population size
A. Abiotic
1. Most important- weather & climate
a. harsh weather slows growth rate
B. Biotic
1. Often density dependent
a. Crowding causes stronger influence
2. Food (ex- grass or other animals)
a. plenty = growth, scarce = decline
3. Predators
a. too many = decline
4. Bacteria & disease

9. 5. Humans affect populations
1. cause populations to decrease
a. disrupt habitats, introduce disease, or introduce non native species
IV. Human Population
A. More than 7 billion
B. Decreased death rate
1. Reasons - better sanitation, hygiene, disease control, & agricultural technology
C. Industrial Revolution
1. Rapid increased growth of human population

10. D. Beginning to put pressure on Earth’s ecosystems
1. possibly 9 billion humans in 50yrs.
E. Science & technology
1. agricultural tech. has allowed efficient production of crops.
a. more food = more people
2. Medical advances
a. Vaccines allow more children to grow to adulthood