Population Ecology
Population-a group of organisms ofone species living in the same placeat the same time that interbreedand compete with each other forresources (ex. food, mates, shelter)
What characteristics are used todescribe a population?
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Geographical distribution – Describeshow a population is spaced
Population Density – The # of
individuals divided by the area
Growth Rate – The change in # within apopulation due to births, deaths,immigration, & emigration
What factors affectpopulation 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 thatenter or leave the population
A population can grow when itsbirthrate is greater than its death rate.
Immigration: the movement of individualsinto an area, is another factor that cancause a population to grow.
Emigration: the movement of individualsout of an area, can cause a population todecrease in size.
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What are exponentialgrowth and logisticgrowth?
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Exponential Growth
Under ideal conditions withunlimited resources, a populationwill continue to grow
Exponential growth occurs when theindividuals in a populationreproduce at a constant rate.
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Exponential Growth
Kruger National Park, South Africa
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Logistic Growth
As resources become less available,the growth of a population slows orstops.
Logistic growth occurs when apopulation's growth slows or stopsfollowing a period of exponentialgrowth.
Logistic growth is characterized by an S-shaped curve.
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Occurs when resources become lessavailable (Slows population growthrate)
Slow population growth rate due to
1.Decrease in birthrate
2.Increase in deathrate
3.Immigration decreases
4.Emigration increases
The largest # ofindividuals anenvironmentcan support
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Limiting Factor: is a factor that causespopulation growth to decrease.
Limited resources
Food
Water
Space
Shelter
Mates
Sunlight
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Density-Dependent Factors
A limiting factor that depends onpopulation size is called a density-dependent limiting factor.
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•Density-dependent limiting factorsinclude:
competition
predation
parasitism
disease
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Density-Independent Factors
Density-independent limiting factorsaffect all populations in similar ways,regardless of the population size.
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unusual weather
natural disasters
seasonal cycles
certain human activities—such asdamming rivers and clear-cuttingforests
