Changes in Population What is a Population? ? A group of organisms of the same species ? living in the same habitat ? at the same time ? where they can freely interbreed How Can Populations Change MortalityNatality (Fertility) Immigration & Emigration Fertility ? Crude Birth Rate (CBR) live births per 1,000 people ? Total Fertility Rate (TFR) avg. number of children born to a woman ? Life Expectancy ? number of years an infant can expect to live ? Natural Increase Rate (NIR) ?Excess of births over deaths results in natural increase ?Excess of deaths over births results in natural decrease Mortality ? Crude Death Rate (CDR) deaths per 1,000 people ? Infant Mortality Rate (IMR) ? number of children who die before their first birthday