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Population Growth Copyright Pearson Prentice Hall Factors Affecting Population Growth Rate • 3 factors affect population growth rate: –Number of births –Number of deaths –Migration • These factors will be directly affected by the availability of resources. Migration • Immigration—movement of individuals into an area that has an existing population • Emigration—movement of individuals out (exiting) of a population • Zero growth when immigration & birth rate are EQUAL to emigration & death rate Exponential growth is characterized by a J-shaped curve. Did you see exponential growth in either the Paramecium lab or human population growth activity? Copyright Pearson Prentice Hall Exponential Growth Under ideal conditions with unlimited resources, and in the absence of disease or predation a population will grow exponentially. Exponential growth occurs when the individuals in a population reproduce at a constant rate. The population becomes larger and larger until it approaches an infinitely large size. Copyright Pearson Prentice Hall Human Population Growth Activity • When the human population levels off, what will it have reached? • Carrying capacity- the maximum number of individuals that a stable environment can support. Human Population Growth Activity • If the carrying capacity of the earth is 9 billion, what year will this number be reached? • What will happen when the earth exceeds it’s carrying capacity? • What factors contributed to the world’s overall population growth over the past 150 years? • Why does a population not level off during the same year it reaches zero population growth? Logistic growth is characterized by an S-shaped curve. It also shows the carrying capacity of the population. Copyright Pearson Prentice Hall Logistic Growth As resources become less available, the growth of a population slows or stops. Logistic growth occurs when a population's growth slows or stops following a period of exponential growth. Logistic growth occurs in natural populations NOT exponential. WHY? Copyright Pearson Prentice Hall Competitive Exclusion Principle • No two species can occupy the same niche in the same place at the same time. WHY? • One species will be eliminated from a community because of competition for the same limited resource. • How did the Paramecium lab demonstrate competitive exclusion?