Population Ecology

Chapter 19

Properties of Populations What is a population?

Group of organisms that belong to the same species and live in a particular place at the same time.

What classifies a group to be considered a population?

1. Population Size -- # of individuals2. Population Density – how crowded is it3. Dispersion (clumped, even or uniform,

random)

Also known as even dispersion.

Population Dynamics Populations are dynamic…meaning they

change in size and composition over time.

1. Birth Rate2. Death Rate (Mortality)3. Life Expectancy4. Age Structure – distribution of individuals

among different ages in a population.5. Survivorship Curves – mortality rate data of

different species tend to conform to 1 of 3 curves.

AGE STRUCTURE GRAPHS

Type I = Likelihood of dying is small until late in life

Type II = Some species the probability of dying doesn’t change throughout life

Type III = Many organisms are very likely to die when young

SURVIVORSHIP CURVES

Measuring Populations (Ch. 19-2)

Demographers study population dynamics. The size of a population depends on four

factors: birth, death, emigration, and immigration.

1. Emigration- movement of individuals out of a population.

2. Immigration- movement of individuals into a population.

Growth rate = birth rate – death rate

Population Growth Type 1

Exponential Growth…”J” shaped curve.

The larger the population gets, the faster it grows.

Limits on Populations

A limiting factor is an environmental factor that prevents or stops a population from growing.

What would be some examples of limiting factors?

Answers

Some limiting factors --- natural disasters, weather, disease, living space, competition, predation, etc.

Population Growth Type 2 Logistic Growth…”S”

shaped curve.

Builds on the exponential model but takes into account limiting factors.

Carrying Capacity- number of individuals the environment can support over a long period of time.

Population Regulation

Density Dependent --- A factor that has an increasing affect as a population increases. Examples --- disease, competition, parasites, and food.

Density Independent --- affects all populations no matter what their size or density is.

Examples – temperature, floods, storms, drought, and habitat destruction.

Human Population Growth(Ch. 19-3) The history…hunter-gathers (500,000 years ago).

Growth of population was very slow due to small populations and a high mortality rate.

Agricultural Revolution (10,000 years ago). Population began to grow fast because of increased food supply.

Bubonic Plague (1347-1352)…wiped out 25% of Europe’s population.

1650…Why did mortality rates decrease?

World War II

Population Growth Today It took most of human history for the

world’s population to reach 1 billion (Year 1800)

It took 27 years for the population to grow from 3 billion to 5 billion (1960-1987).

20% of the world’s population lives in developed countries. (includes modern, industrialized countries)

80% lives in developing countries. (poorer countries & populations growing faster.)