Population Ecology

Chapter 19

Understanding Populations (Ch. 19.1)

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 Expectancy

Age Structure – distribution of individuals among different ages in a population.

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 rateTotal Growth rate = (B – D) + (I – E)

Population Growth Type 1

Exponential Growth…”J” shaped curve.

The larger the population gets, the faster it grows.

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)

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 – 12,000 years ago). Population began to grow fast because of increased food supply.

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

1650…Mortality rates decrease…reason = better sanitation and hygiene, control of disease, better sources of food, improved economics.

World War II…kaboom!

World Population Distribution Today

Asia – 60.5%Africa – 13.4%Europe – 11.9%Latin America – 8.5%North America – 5.2%Oceania - .5%

US Statistics:Growth Rate = .9%Fertility Rate = 1.9Literacy Rate = 99%GNI Per Capita = $47,000