5-1 and 5-2 Population Growth Charles Darwin calculated that a single pair of elephants could increase to a population of 19 million individuals within 750 years. The fact that the world is not overrun with elephants is evidence that some factor or factors restrain the population growth of elephants.

1. Characteristics of populations A. 4 important characteristics 1. Density 2. Geographic distribution 3. Growth rate 4. Age Structure 2. Population density A. Number of individuals per unit area. B. Can vary tremendously depending on the ecosystem and species.

3. Population Growth A. Growth rate is the amount by which a population’s size changes in a given time. B. Growth depends on four processes: 1. Number of births 1. Number of births 2. Immigration 3. Emigration 4. Number of deaths

C. Immigration is the movement of individuals into an area 1. Causes the population size to increase. D. Emigration is the movement of individuals out of an area 1. Causes the population to decrease in size.

4. The Exponential Growth A. The exponential growth 1. Organisms in a population reproduce at a constant rate, and the larger the population the faster it will grow. 2. As long as there are no restraints such as predation, space, resources, diseases and competition a population will grow exponentially.

B. Limits to the Exponential Model 1. This happens for a short period of time and under rare conditions. 2. Limiting factors: a factor that restrains the growth of a population, like drought, scarce resources, scarce space, diseases, predation and competition. 3. End result: declining birth rate and an increasing mortality rate.

5. The Logistic Growth A. Logistic growth 1. Accounts for resources becoming less available, which either slows or stops growth rate completely. Usually occurs after exponential growth. 2. Carrying Capacity (K): the number of individuals the environment can support over a long period of time.

Logistic Growth of fur seals

5:2 Limits to Growth Limits to Growth

1. Limiting Factors A. Is a factor that causes population growth to decrease. B. Density Dependent Factors 1. Become limiting when the population density reaches a certain level. 2. Affect large, dense populations. 3. Include factors such as competition, predation, parasitism, and disease.

C. Density Independent factors 1. Will affect all populations in similarways, regardless of the population size. 2.. Examples include: weather, Natural disasters, seasonal cycles, damming rivers and clear-cutting forests. 2.. Examples include: weather, Natural disasters, seasonal cycles, damming rivers and clear-cutting forests.

7. Predator prey relationship A. Population size is often regulated by nature. B. Ex. Lynx and Snowshoe hare 1. Each species keeps the others population size in check, or under control for the environment.

Snowshoe hare and Lynx populations (classic example)