Lecture 26 27 Population Demography KRG

Lecture 26 27 Population Demography KRG - How Does Age...

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How Does Age Affect Growth of Populations? How Does Age Affect Growth of Populations? The logistic model assumes : 1. Birth/death and density influences impact growth instantaneously 2. All individuals genetically the same 3. All individuals equal in terms of birth and death – age doesn’t matter
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But We Know This Isn’t Realistic Individuals have different probabilities of living, dying and reproducing … Age structure alters population growth Baby boomers Baby boomers’ babies
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Which country’s population is growing fastest? Life Tables assist with age-specific dynamics h Life tables summarize mortality and survival rates = static life table (“vertical life table”) h Or life tables follow a cohort of individuals and measure survival and fecundity = cohort life table (“horizontal life table”) Lagrangian Lagrangian Eulerian Eulerian
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Static Life Table Dall Mountain Sheep - Alaska Static life tables h show survivorship with age h 3 basic shapes Annual plant High overall survivorship High overall survivorship Constant risk of mortality Constant risk of mortality Low juvenile survivorship Low juvenile survivorship
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Static life tables don’t tell everything… h Show survivorship and mortality h But don’t tell us if population is increasing, decreasing or remaining the same h We need to know something about reproduction h Cohort life table follows individuals (usually females) through time … 10 Cohort Life Table Annual Grass
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R o , the net reproductive rate • If R o > 1, population is increasing • If R o = 1, population is steady • If R o < 1, population is decreasing R o is simply whether a female is replacing herself, or not How Do Species Vary in Survival and
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Lecture 26 27 Population Demography KRG - How Does Age...

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