Chapter 19-1 Populations

Objectives

• Explain the difference between population size, density, and dispersion

• Describe the three main patterns of population dispersion

• Explain the importance of a populations age structure

• Contrast the three main types of survivorship curves

Populations

• Defined by place & time

• Size: number of individuals– How do you find size? Count everyone?

• U.S. census

– Estimation: take a small sample and extrapolate to a larger area

• Density: How crowded?– Individuals per unit volume

Density by country

Country Population Area (km²) Density—World 6,445,398,968 148,940,000 43Singapore 4,425,720 692.76 389United States 295,734,134 9,631,418 30Australia 20,090,437 7,686,850 2

Density by city

Dispersion patterns

Population dynamics

• Birth rate: number of births over a period of time– Also fertility rate: How many offspring each female

has• Developed ~ 1/2• Developing ~ 5/6

• Death/mortality rate: number of births over a period of time

• Life expectancy: how long an individual is expected to live– Girls live longer

Age structure Shows distribution of individuals among different groups.

Explain how it is possible to conclude that the life expectancy of a person in a stable population is longer than that of a person in an expanding population.

How can you tell that women have a longer life expectancy than men?

Predictions from survivorship curve

• Which countries population has the potential for rapid growth?

• Bottom heavy curves indicate that many young have been added to the youngest & most reproductive age group.

Survivorship curves

• Show how many individuals survive over time

• Three different trends• Type I: you’ll probably live until old age

– Elephants: Few young, lots of care

• Type II: you have an even chance to survive no matter how old

• Type III: you’ll probably die young, but if you survive you’ll live to an old age.– Insects: Many young, little care

Explain how populations can be the same size but have different

densities• It depends on both

the number of people and on space. Two populations with the same number can have different numbers depending on the space.

Explain why even distributions usually result from social interactions between individuals

• Even distributions result when organisms attempt to get as far away from each other as possible. Carnivores have well defined territories that keep individuals apart.

Stay out of my territory

Why might natural selection favor a high reproductive rate in Type III

organisms?• Though many young die the surviving

young are well adapted to the environment

• More young

also means more

variation

• Define Birth Rate– Number of births over a period of time

• Define Death Rate– AKA mortality Rate– Number of deaths over a period of time

Explain two difficulties an ecologist might have in counting a population of migratory birds. Develop & explain a method for estimating the size of such

a population• Flocks are too

numerous, widespread and mobile.

• Tagging individuals is one solution

• Find a bottle neck• Count numbers

passing over a period of time

Counting a herd of zebras can be tough