Section 1: How Populations Grow Chapter 5: Populations Section 1: How Populations Grow

Properties of Populations Population – a group of organisms of the same species that live in a specific geographical area and interbreed Population Size – the number of individuals in the population Population Density – measure of how crowded a population is the number of individuals per unit of area Dispersion – the spacing of organisms in a population clumped even random

Changes in Population Size Birth Rate: the number of births occurring in a period of time in the U.S. there are about 4 million births per year Death Rate: the number of deaths in a period of time in the U.S. there are about 2.4 million deaths per year Growth Rate: birth rate – death rate depends on birth rate, death rate, emigration, and immigration Immigration: individuals move into its range from elsewhere Emigration: individuals move out of the population’s range Age Structure: the number of males and females of each age a population contains

Age Structure

Age Structure The shape of the age structure diagram tells you: if a population is increasing, stable, or shrinking Population growth momentum; even if people are having less children, the effect won’t take place until much later when the children reach reproductive maturity. Scientists use age structure diagrams to: Compare age groups such as pre-reproductive ages Compare the number of males to females Scientists use the shape of the graph to determine: If a population is growing, shrinking, or staying the same Growth momentum; how soon overpopulation will become a problem

Age Structure

Population Growth Exponential Model – a model of growth describing an unrestricted population that increases very rapidly forever assumes birth rates and death rates are constant with births outnumbering deaths & that there are unlimited resources not realistic because resources become limited as the population grows

Population Growth Logistic Model – a model of growth describing a population that increase very rapidly but then levels off ; levels off(population stabilizes) at the carrying capacity which is the largest population that an environment can support at any given time assumes birth rates & death rates are not constant & that birth and death rates vary with population size the death rate increases when resources become limited When there is no population growth the line is horizontal; at this time the number of births and deaths are equal Logistic Models display in a ‘S” shape

Section 2: Limits to Growth Chapter 5: Populations Section 2: Limits to Growth

Limiting Factors Limiting Factor: factor that controls the growth of a population Acting separately or together, limiting factors determine the carrying capacity of an environment for a species Charles Darwin recognized the importance of limiting factors (natural selection) in shaping the history of life on Earth

Density-Dependent Limiting Factors Density Dependent Factors – something that affects the population size due to the population density examples: competition, herbivory, parasitism, disease, and stress from overcrowding application example: millions of people moving to California will cause a food shortage there

Density-Independent Limiting Factors Density Independent Factors – something that affects the population size regardless of the population density examples: hurricanes, droughts, or floods and natural disasters such as wildfires application example: millions of people moving to California won’t cause an earthquake

Section 3: Human Population Growth Chapter 5: Populations Section 3: Human Population Growth

Historical Overview Human Population Growth – the number of people on the planet is still growing rapidly. We are now just above 7 billion people. If our population gets too high, it could put a strain on the environment; the ever growing population is the greatest threat to the world’s future increased emissions competition for water, space, food, etc. destruction of natural habitat

Patterns of Human Population Growth Demography: the scientific study of human populations Examines characteristics of human populations and attempts to explain how those populations will change over time Birthrates, death rates, and the age structure of a population help predict why some countries have high growth rates while other countries grow more slowly Demographic Transition: a dramatic change from high birthrates and death rates to low birthrates and death rates US, Japan, & Europe