Population: A group of organisms of the same species, living together and interbreeding.

• Populations usually are too large or spread out to study every individual.

• Ecologists use graphs to organize information about populations.

• The human population has changed drastically in the history of mankind.

• Populations affect and are affected by their environment and the other organisms in it.

Population Growth

• Growth curve: graph showing the number of individuals in a population over time.

• Biotic Potential: rate at which a population will grow if all individuals survive and reproduce at maximum capacity.

Linear Growth

Linear Growth:

Growth that occurs in a straight line. (This generally doesn’t happen in nature.)

Exponential Growth of Cells

Exponential Growth:

Growth at an ever-increasing rate; calculated using exponents. (The population has reached biotic potential)

J-shaped curveShows 2 phases:

1.Lag phase: little or no increase in population.

2.Exponential phase: period of exponential growth.

(Can you label these on the graph?)

http://www.biologycorner.com/bio4/notes/popgrowth.php

S-shaped CurveDepicts limits on population due to environmental factors.

Carrying capacity: maximum number of individuals that an ecosystem is capable of supporting.

(Label lag phase, exponential phase and carrying capacity.)

Limiting Factors: Variables in the

environment that limit the growth

rate.• Food

• Disease

• Forest Fires

• Dutch Elm Disease

• Kaibab deer

• FIV virus: Evolutionary Arms Race- Wildcats

Human Population Growth

Demographic Trends

Demography: the study of human population growth characteristics.

Why is the human population so successful?

1. Better Sanitation.

2. Increased food productions (agriculture).

3. Control of disease. (medical technology)

Video Clip: Population Explosion

Growth Rate

Birth Rate: the number of individuals being born into a population.

Death Rate: The number of individuals dying from a population.

The difference between the birth rate and death rate is the growth rate.

population equilibrium

• a situation in which the population stays at the same level, because the number of deaths is the same as the number of births

The Population of the World

The solid line in this graph shows estimates of the size of the world's population over the last two millennia. The estimates from 1800 to 1991 are based on more accurate data than

those before. The dotted line shows what would happen if

exponential growth continued to the year 2100.

As you can see, the world's population has been growing exponentially (except during the years of the black death). How long will it continue to do so? (Since the graph was drawn, the world's population has reached 6.5 billion; that is, in 2007 we are still on course.) But can it continue indefinitely?

Surely not.

Influenza and Pneumonia Pandemic

Excess Annual Death Rates from Influenza and Pneumonia: 1887-1921

Age StructureGraph that refers to portions of

populations at different age levels.

http://www.uwlax.edu/faculty/skala/Age-Structure.htm

What does this graph tell us about the population?

Is this population stable?

Yes?

http://www.uwlax.edu/faculty/skala/Age-Structure.htm

How do we know?There are the same number of Pre- reproductive and post-reproductive

individuals.

http://www.uwlax.edu/faculty/skala/Age-Structure.htm

In 1980, does country X exhibit an age structure more typical of a developing nation or an industrialized nation? Explain.

What might account for the age structure predicted for the year 2080?