1. Populations
Objective: A4 - Analyze how populations & communities respond to abiotic & biotic factors and recognize that long-term survival of a species is dependent on changing resources that are limited
Review:
Population - a group of organisms, all of the same species living in a specific area.
Density - # of organisms
3 important characteristics of a population are:
distribution
density
growth rate

2. the number of individuals per unit area 1
Population density –
the number of individuals
per unit area
3 factors that can affect population:
- number of births
- number of deaths
- number of individuals that enter or
leave the population
Immigration – movement of individuals into an area
Emigration – movement of individuals out of an area

3. Population Growth Population Growth of Houseflies2
Population Growth of Houseflies
1 million
500,000
100
One year
Population size
● J-shaped growth curve
— illustrates exponential population growth

4. Population Growth of Houseflies
1 million
500,000
100
One year
Population size 3
Exponential growth – occurs when the individuals in a population reproduce at a constant rate
(as a population gets larger, it also grows at a faster rate)
No limits on growth
Under ideal conditions with unlimited resources
Could not occur indefinitely in nature

5. Logistic growth – occurs when a population’s growth slows or stops 4
Logistic growth – occurs when a population’s growth slows or stops
- as resources become less available, following a period of exponential growth
Exponential
Limits on growth
A S-shaped curve illustrates logistic growth

6. Carrying capacity 5
Carrying capacity – largest number of individuals of a population that a given environment can support

7. 6

8. Limiting factor – a factor that causes population growth to decrease7
Limiting factor – a factor that causes population growth to decrease
Any biotic or abiotic factor that restricts the existence, numbers, reproduction, or distribution of organisms
Examples
Lack of food
Overcrowding
Competition for resources

9. Characteristics of Population Growth8
Characteristics of Population Growth
Exponential growth
Carrying capacity
J curve
S curve
Population
Time
DISEASE
SPACE
PREDATORS
FOOD

10. 2 kinds of limiting factors:9
2 kinds of limiting factors:
Density-dependent limiting factor
Exp. competition, predation,
parasitism, disease
Density-independent limiting factor
Exp. Unusual weather, natural
disasters, seasonal cycles,
certain human activities
biotic
abiotic

12. Resources Glenco Interactive Chalkboard 2003
Prentice Hall Biology 2004