population growth sc.912.l.17.5. population growth what factors affect population size? copyright...
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Population Growth
SC.912.L.17.5
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Population Growth
What factors affect population size?
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Population Growth
Three factors can affect population size:• the number of births• the number of deaths• the number of individuals that enter or leave the
populationA population can grow when its birthrate is greater than its death rate.
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Population Growth
Immigration, the movement of individuals into an area, is another factor that can cause a population to grow.
Emigration, the movement of individuals out of an area, can cause a population to decrease in size.
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Exponential Growth
What are exponential growth and logistic growth?
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Exponential Growth
Under ideal conditions with unlimited resources, 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.
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Exponential Growth
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Exponential Growth
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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.
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Carrying Capacity: the maximum number of individuals the environment can hold
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Limiting Factors
– What factors limit population growth?
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Limiting Factors
• The primary productivity of an ecosystem can be reduced when there is an insufficient supply of a particular nutrient. • Ecologists call such substances limiting nutrients.
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Limiting Factors
• A limiting nutrient is an example of a more general ecological concept: a limiting factor.
• In the context of populations, a limiting factor is a factor that causes population growth to decrease.
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Density-Dependent Factors
• Density-Dependent Factors• A limiting factor that depends on population size is
called a density-dependent limiting factor.
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Density-Dependent Factors
– Density-dependent limiting factors include: • competition• predation• parasitism• disease
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Density-Dependent Factors
– Density-dependent factors operate only when the population density reaches a certain level. These factors operate most strongly when a population is large and dense.
– They do not affect small, scattered populations as greatly.
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Density-Dependent Factors
– Competition• When populations become crowded, organisms
compete for food, water space, sunlight and other essentials.• Competition among members of the same species is a
density-dependent limiting factor.
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Density-Dependent Factors
• Competition can also occur between members of different species.
• This type of competition can lead to evolutionary change.
• Over time, the species may evolve to occupy different niches.
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Density-Dependent Factors
– Predation• Populations in nature are often controlled by
predation. • The regulation of a population by predation takes place
within a predator-prey relationship, one of the best-known mechanisms of population control.
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Density-Dependent Factors
Wolf and Moose Populations on Isle Royale
Moose Wolves
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Density-Dependent Factors
– Parasitism and Disease• Parasites can limit the growth of a population.• A parasite lives in or on another organism (the host)
and consequently harms it.
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Density-Independent Factors
• Density-independent limiting factors affect all populations in similar ways, regardless of the population size.
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Density-Independent Factors
– Examples of density-independent limiting factors include: • unusual weather
• natural disasters
• seasonal cycles
• certain human activities—such as damming rivers and clear-cutting forests