Describing PopulationsCh. 4 sec. 2

From 1900 to 2000, the white-tailed deer population of New York state

grew from about 20,000 to more than 1 million. Densities of more than 100

deer per sq mi occur in some metropolitan areas.

• All the members of a species living together in the same place at the same time.

• Ex. Daisies found in a field in Latrobe, PA. They are NOT in the same population as all of the daisies found in a field in Buffalo, NY.

Population Defined

• Number of individual organisms present in a specific population at a specific time.

• Size is an indicator of overall health and changes over time can indicate success or struggle.

• The story of the Passenger Pigeon. LINK • Video

Population Size

Did You Know? The passenger pigeon was once North America’s most abundant bird. Hunting drove them to extinction in less than 100 years.

• Number of individuals within a population per unit area.

• High population density can be good and bad.– The good: easy to group together, easy to find

mates, protection from predators. – The bad: conflict, competition, disease

transmission, vulnerability to predators, etc.

Population Density

• Random = no particular pattern.

• Uniform = evenly spaced throughout an area.

• Clumped= arranged according to availability of resources needed to survive. – This is the most common pattern.

Population Distribution

• Age structure: relative numbers of organisms of each age in a population.

• Sex ratio: proportion of males to females.

• Lack of balance in either can cause problems.– What issues can you

think of?

Age Structure and Sex Ratio

1. How is a population’s size related to its well being?2. Which population of flamingos is most dense: 15

flamingos in a 5-square meter area, or 40 flamingos in a 10 square meter area?

3. Paleontologists use fossils to study past life on Earth. They have documented several times in Earth’s history when massive numbers of species have declined and then disappeared from the fossil record all at once. Why do you think population ecologists studying living organisms might be interested in these mass extinction events?

Review Questions