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Populations

Populations. Chapter 8 section 1. Population. Population: All the same members of a species living in the same place at the same time. Properties of Populations. Density: The number of individuals per unit area Dispersion: The relative arrangement of a population’s individuals Even

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Populations

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  1. Populations Chapter 8 section 1

  2. Population • Population: All the same members of a species living in the same place at the same time

  3. Properties of Populations • Density: The number of individuals per unit area • Dispersion: The relative arrangement of a population’s individuals • Even • Clumped • Random

  4. Density

  5. Dispersion

  6. Three factors can affect population size: the number of births, the number of deaths, and the number of individuals that enter or leave the population. The J-shaped curve indicates that the population is undergoing exponential (eks-poh-NEN-shul) growth. Exponential growth occurs when the individuals in a population reproduce at a constant rate.

  7. In the context of populations, a limiting factor is a factor that causes population growth to decrease. • A limiting factor that depends on population size is called a density-dependent limiting factor. Density-dependent factors become limiting only when the population density—the number of organisms per unit area—reaches a certain level. Density-dependent limiting factors include competition, predation, parasitism, and disease. Density-independent limiting factors affect all populations in similar ways, regardless of the population size. Unusual weather, natural disasters, seasonal cycles, and certain human activities—such as damming rivers and clear-cutting forests—are all examples of density-independent limiting factors. In response to such factors, many species show a characteristic crash in population size. After the crash, the population may soon build up again, or it may stay low for some time.

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