Chapter 5 – Populations

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How do ecologist study populations?
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By studying their geographic range, density and distribution, growth rate and age structure.
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Population density
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The number of individuals per unit area
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Geographic Range
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The area inhabited by a population
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Growth Rate
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Determines whether the size of the population increases, decreases, or stays the same.
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Age Structure
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The number of males and females of each age a population contains
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What factors affect population growth?
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Birthrate, Death rate and the rate at which individuals enter or leave the population(immigration and emigration)
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Immigration
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The process where a population may grow if individuals move INTO its range from elsewhere.
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Emigration
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The process where a population may decrease in size if individuals move OUT of the population.
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What happens during exponential growth?
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Under ideal conditions with unlimited resources, a population will grow exponentially.
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Exponential Growth
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When the size of each generation of offspring will be larger than the generation before it.
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What is logistic growth?
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This occurs when a population’s growth slows and then stops, following a period of exponential growth.
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What are the phases of logistic growth?
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Phase I = Exponential growth Phase II = Growth slows down Phase III = Growth stops
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Carrying capacity
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The maximum number of individuals of a particular species that a particular environment can support.
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What factors determine carrying capacity?
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Limiting factors
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What limiting factors depend on population density?
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Density-DEPENENT limiting factors such as: competition, predation, herbivory, parasitism, disease, and stress from overcrowding.
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What limiting factors do NOT typically depend on population density?
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Density-INDEPENDENT limiting factors such as: unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires.
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Limiting factor
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A factor the controls the growth of a population
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Density-dependent limiting factors
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competition, predation, herbivory, parasitism, disease, and stress from overcrowding.
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Density-independent limiting factors
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unusual weather such as hurricanes, droughts, or floods, and natural disasters such as wildfires.
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How has human population size changed over time?
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Tends to increase dramatically over time
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Why do population growth rates differ among countries?
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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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Demography
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The scientific study of human population.
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Demographic transition
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A dramatic change from high birthrates and death rates to low birthrates and death rates.
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The number of individuals of a single species per unit area is known as what?
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Population density
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The movement of individuals into an area is called what?
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Immigration
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The area inhabited by a population is known as its what?
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Geographic range
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The maximum number of organisms of a particular species that can be supported by an environment is called what?
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Carrying capacity
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What is the difference between immigration and emigration?
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Immigration -> move In Emigration -> move out
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Name an example of a density-INdependent limiting factor?
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Weather such as – Hurricanes, droughts, floods Natural disasters such as – wildfires
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The scientific study of human populations is called what?
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demography
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When is the demographic transition considered complete?
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A population growth stops
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What factors did Thomas Malthus think would eventually limit human population?
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Competition (war), limited resources (famine), parasitism (disease) + other density dependent factors

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