Monitoring Changes in Populations Science Bennett

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