Monitoring Changes in Populations

ScienceBennett

Population Growth

• The population of humans on the planet remained stable for thousands of years before the invention of agriculture.

• When a significant number of human societies switched from hunting and gathering to agriculture, the population began to grow.

• In the mid-1960s the global human population reached about 500 million.

• Given a current annual growth rate of 1.55 %, which adds 80 million people a year, it is estimated that the global human population will be 8 billion by the year 2013.

Factors that affect population size

• Natality (births) = the number of offspring of a species born in one year

• Mortality (deaths) = the number of individuals of a species that die in one year

• Immigration = the number of individuals of a species moving into an existing population

• Emigration = The number of individuals of a species moving out of an existing population

Open and Closed populations

• In most natural ecosystems, all four factors (natality, mortality, immigration and emigration) are acting on the population of each organism. These populations are said to be open populations.

• In populations where immigration and emigration do not happen (for example in laboratory settings or game reserves), these are considered closed populations.

Factors that cause changes in populations

• Density-independent factors affect members of a population regardless of density:

• flood• fire,• spraying with pesticides• change in climate or temperature• destruction of the habitat• drought

• Density-dependent factors affect the population because of the density:

• food shortage• Competition for mates, breeding areas, habitat• Disease• Introduction of an exotic species• Increased predation• Competition for water and other resources

Population Histograms

• Population histograms are useful when studying populations of long-lived organisms, such as humans.

• The shape of the pyramid helps us to predict the changes in the population.

Examples of Population Histograms

• See page 75, Nelson Science 10

• See Blackline Master 2.9c- Population Graphs