BIOL 2102 Demography

What is demography?

The study of population characteristics (births, deaths, migration) and how they change over time to influence population growth.

What does a life table summarize?

Survival rates and reproductive rates of individuals across different age groups in a population.

Why do demographers typically consider females only when constructing a life table?

Because females directly produce offspring, so they determine the population’s reproductive output.

How is reproductive output measured?

As the average number of female offspring produced per female in a specific age group.

Why is age important when measuring reproductive rates?

Because reproduction varies by age—young individuals may not reproduce, middle-aged individuals reproduce most, and older individuals reproduce less.

What are the axes of a survivorship curve?

X-axis: age (or percentage of lifespan); Y-axis: number of individuals surviving (often on a log scale).

What is the shape and meaning of a Type I survivorship curve?

High survival in early/mid life, steep decline in old age; indicates few offspring with high parental care.

What is the shape and meaning of a Type II survivorship curve?

Constant decline; indicates a constant death rate throughout life.

What is the shape and meaning of a Type III survivorship curve?

Steep early drop, then levels off; indicates high early mortality and many offspring with little parental care.

What does a survivorship curve tell you about a population?

How survival changes across the lifespan and when most individuals die.

Give an example of a Type I survivorship curve organism.

Humans or elephants.

Give an example of a Type II survivorship curve organism.

Birds or small mammals.

Give an example of a Type III survivorship curve organism.

Fish, marine invertebrates, or many plants.