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Chapter 45Population Ecology: A Summary
AP BiologySpring 2011
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Population Demographics
•Population density: number of individuals per a certain area
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Population Demographics
•Population distribution: where individuals are positioned in a certain area▫3 types
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Population Demographics
•Clumped distribution: pattern is one where all individuals are in a small area▫Ex. Surrounding water supply
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Population Demographics
•Uniform distribution: individuals are evenly spaced
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Population Demographics
•Random distribution: individuals have no uniformity to their placement
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Elusive Heads to Count•Quadrants are plots of land of a standard
size used for counting the number of organisms
•The capture-recapture method is used to estimate the size of a population of animals▫Sample size must be large enough to gather
significant information ▫The animals captured must have no bias, such
as being easier or more difficult to catch
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Population Size and Exponential Growth
•Members of a population may leave (emigration) or enter a new population (immigration)▫Ms. Warren
emigrated from Canada, and immigrated to the US
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Population Size and Exponential Growth •Zero population growth: number of
individuals born equals the number dying •Per capita growth
rate: equals the birth rate minus the death rate ▫If per capita growth rate
is more than zero, the population is exhibiting exponential growth J shaped curve
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Population Size and Exponential Growth •Biotic potential: indicates the largest
amount of increase that can occur in that particular population
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Limits on Population Growth
•Carrying capacity: largest number of individuals that a certain environment can support ▫S shaped
curve indicative of how a population naturally changes
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Limits on Population Growth
•Limiting factors: components that are not plentiful and may restrict population growth ▫Density dependent factors▫Density independent factors
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Limits on Population Growth
•Density dependent factors: those that become more critical as the population increases▫Ex. Food, water, incidence of disease
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Limits on Population Growth
•Density independent factors: those that are not influenced by the size of a population ▫Ex. Floods, fires, earthquakes, natural
disasters
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Life History Patterns •Life tables: illustrate the number of
individuals that survive in various age categories
•Survivorship curve: visual representation of age-specific survival of a population
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Life History Patterns
•Type 1 curve: shows tat the individuals usually survive until old age ▫Animals exhibiting type 1 curve produce
small amount of offspring that require much care
▫Ex. Humans▫These animals exhibit K-selection, few
offspring needing much care
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Life History Patterns
•Type 2 curve: illustrates that the survival rate does not relate to age▫Ex. Squirrels
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Life History Patterns
•Type 3 curve: chows that the majority of individuals do not survive to maturity ▫Animals exhibiting type 3 produce many
offspring that do not require much care▫Ex. Sea urchins ▫These animals exhibit R-selection with
many offspring needing little care
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Life History Patterns
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Natural Selection and Life Histories •Life history traits can change as a
response to an alteration in the types of predators ▫Ex. Shown by 2 isolated populations of
guppies where there were different predators
▫The life history of the cod population in the North Atlantic changed due to over-fishing
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Human Population Growth
•Human population’s current rate of increase is approximately 1.1%
•This rate of growth is due to the fact that humans can spread easily into new habitats
•Man has developed fire, tool making abilities that are passed on from one generation to the next
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Human Population Growth •Humans have developed new technologies
to increase the carrying capacity of the environment▫Man learned how to cultivate crops, raise
livestock
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Human Population Growth
•Human population has learned how to overcome some limiting factors▫Man learned how to combat many diseases
and use fossil fuels for energy production •Density dependent factors may become of
the utmost importance due to overpopulation
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Fertility Rates and Age Structure •Total fertility rate: the average number of children born to each woman of reproductive age
•The fertility rate worldwide has decreased from 6.5 to 2.7 in the last 50 years
•This decrease still puts the worldwide fertility rate above the number that keeps the population at a constant level
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Fertility Rates and Age Structure •One third of the world’s population is not
yet in the reproductive category•China has initiated a system of rewards to
encourage a lower national fertility rate
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Population Growth and Economic Effects •Demographic transition model:
connects industrial development and changes in population growth rates
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Population Growth and Economic Effects •In countries where industrialization has
not yet occurred, the birth rate is high ▫Children are needed to perform duties on a
farm ▫Ex. Many African countries
•In industrial nations, the birth rate declines, ex. United States▫Industrialized nations use a larger
percentage of resources of the world •In post-industrialized nations, the
population size may increase
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Rise of the Seniors
•The amount of individuals over age 65 is increasing
•Fertility rates are declining•Individuals are living longer due to
medical advances•Society may have trouble supporting the
increase in retired individuals