Populations
The way a population changes depends on many things, including its age structure, the rates at which individuals are added or removed from the population, and factors in the environment that limit its growth.
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5.1 How Populations Grow
Researchers study populations’ geographic range, density and distribution, growth rate, and age structure. The factors that can affect population size are the birthrate, the death rate, and the rate at which individuals enter or leave the population. Under ideal conditions with unlimited resources, a population will grow exponentially. Logistic growth occurs when a population’s growth slows and then stops, following a period of exponential growth. |
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5.2 Limits to Growth
Acting separately or together, limiting factors determine the carrying capacity of an environment for a species. Density-dependent limiting factors operate strongly when population density reaches a certain level. Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding. Density-independent limiting factors affect all populations in similar ways, regardless of population size and density. Unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wild-fires, can act as density-independent limiting factors. |
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5.3 Human Population Growth
The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically 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. |
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