Population Ecology NotesMrs. Walker

Demography• Demographers are scientists who study population growth.

When studying population growth, you will often refer to charts and graphs. The following graphs and charts display examples of population growth.

Linear Growth• Linear Growth – In other words, growth in a straight line. Your

hourly wage would grow constantly.

Logistic Growth• Logistic or S-Shaped Growth Curve – Most populations grow

this way!!

Population Growth• Point A: Lag Phase Many organisms are reproducing and

the population is just getting started.

Population Growth Continued• Point B: Exponential Growth The numbers of organisms are

increasing rapidly because there are good environmental conditions, enough food and shelter and few predators.

Population Growth Continued

• Point C: Carrying Capacity (represented by the letter K) the maximum number of organisms the environment can support.

Population Growth Continued

• This population has reached carrying capacity because of two types of limiting factors….

• Density-Dependent Factors: factors that limit the population size because there are too many organisms. • Examples are: food, shelter, & disease

• Density-Independent Factors: factors that limit the population size regardless of the number of organisms. • Examples are: weather, natural disasters, & temperature

Population Growth Continued• Point D: Stabilization Phase The population levels out and

will remain at or below the carrying capacity.

What other factors limit population size?• Other Factors that Limit the Population Size are:

predation, competition, and crowding/stress.• Predation: Predatory-Prey Relationships are important for the

health of natural populations. Usually in natural populations, the young, weak, or diseased members are caught by predators.

What other factors limit population size?• Competition: When the population number increase in an area,

competition increases until eventually the demand is greater than the supply and the population size will reach its carrying capacity and the population will stabilize.

• Crowding/Stress: Crowding of organisms can cause stress-related effects such as fighting, disease, infertility, and other odd behaviors.

Human Population Growth• Human Population: The human population has been growing

exponentially over the past 100 or so years. This is because of the introduction of medicine, technology, and longer life spans.

Human Population Growth• What are some consequences of the rapid growth of the

human population?