Chapter 10: Population Growth

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Lecture 7

• Chapter 10 Population Growth

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Learning Objectives

• Construct
• Life table (columns 1-5)
• Explain
• All columns (1-8) of life table
• Contrast
• All the different types of life tables
• Discuss
• Mortality and survivorship curves

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Life Insurance Premiums
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Life Tables

• Constructed using age data from a population
• Help ecologists to understand life history of
  organisms
• Help life insurance agents predict the
  probability that youll reach a certain age

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Columns

• Each column of a life table gives different
  information
• First two are easiest, others require a little
  math

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First Column

• Gives the interval for each age (x)
• Could be years, months, days
• Could be life stages egg, larva, adult

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Second Column

• Second column called nx
• Gives the number of individuals

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Third Column

• Called lx or survivorship
• How to remember?
• Gives proportion surviving to stage x
• Hint l1 is always 1.00

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Fourth Column

• Proportion of the original cohort that dies
• Derived from 3rd columnDifference between lx and
  lx1
• Can you think of another way to calculate?

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Fifth Column

• Called age specific mortality rate or qx
• Divide dx by lx
• Can you think of another way?

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Gypsy Moth Life Table

• Eggs from single cohort followed until death
• Note first column is different

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Annual Plant Life Table

• Question what is an annual plant?

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Yield Table

• This style is interesting to foresters
• Note the dbh measurement
• Diameter at Breast Height
• Why might this be better for them?

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Life Tables Two Types

• Cohort
• Static

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Dynamic Life Tables

• Made by following groups of individuals over time
• Also called cohort life table
• All individuals born in same time period
• Usually take a long time to make
• Must wait for every individual to die

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Cohort Life Table Example

• Galapagos finch study
• Marked every single bird born
• Followed fates for decades!!!
• Noted age at death

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Static Life Table

• Relatively quick to make
• Assembled from observations of many cohorts
• Based upon age of death
• No need to wait for death to occur
• Also called time-specific life table

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Static Life Table Example

• Study of bighorn sheep
• Age of death determined by horns

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7th Inning Stretch
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Mortality Curves

• Plots age specific mortality rate from life table
• How are these similar?
• Why are they similar at that point?
• How do they differ?

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Survivorship Curves

• Made from survivorship data in life tables
• Specifically, lx data
• Show percent of population living as a function
  of time
• Draw all three

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Type I Survivorship Curve

• Low infant mortality
• High survival to old age
• Humans

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Type II Survivorship Curve

• Equal chance of survival at every stage of life
• Squirrels

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Type III Survivorship Curve

• High infant mortality
• Little chance of surviving to adulthood
• Oysters, clams

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Birds vs. Deer

• Song sparrow
• Red deer

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