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Chapter 5 How Populations Grow Characteristics of Populations Population density The number of individuals per unit area. Varies depending on the species and its ecosystem. Population Growth 3 factors that affect population size The number of births The number of deaths The number of individuals that enter or leave the population. Population Growth A population can grow IF: The number of births is higher than the number of deaths. More individuals move into the population than out of it. (Immigration) Population Growth A population will stay the same size IF: There are the same number of births as deaths. The same number of individuals move into the population as move out of the population. Population Growth A population will decrease in size IF: There are more deaths than births More individuals move out of the population than into it. (Emigration) Immigration vs. Emigration Immigration is the movement of individuals into a population. Immigration = In Emmigration = Exit Exponential Growth When the individuals in a population reproduce at a constant rate. * Under ideal conditions, a population will grow exponentially. Exponential Growth of an Elephant Population Logistic Growth Occurs when a populations growth slows or stops following a period of exponential growth. Usually caused by a population reaching carrying capacity. Logistic Growth

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