Chapter 10 Population Dynamics

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Chapter 10 Population Dynamics
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Estimating Patterns of Survival

• Three main ways of estimating patterns of
  survival within a population
• Identify a large number of individuals that are
  born about the same time (cohort) and keep
  records of them from birth to death ---gt cohort
  life table
• Record the age at death of a large number of
  individuals ---gt static life table
• Determine patterns of survival for the population
  from the age distribution

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Static Life Tables and Survivorship Curves
Example Survival pattern of Dall sheep
Plotting number of survivors against age produces
a survivorship curve
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Types of Survivorship Curves

• Type I Survivorship Curve
• A pattern in which most of the individuals of
  the population survive to maturity
• Or, most individuals of the population do not
  die until they reach some genetically programmed
  uniform age

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Types of Survivorship Curves cont.

• Type II Survivorship Curve
• Relatively constant death rates with age
• Equal probability that an individual will die at
  any particular age

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Types of Survivorship Curves cont.

• Type III Survivorship Curve
• A pattern in which their is an extremely steep
  juvenile mortality and a relatively high
  survivorship afterward
• Most offspring die before they reach
  reproductive age

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Age Distribution

• Age distribution can tell you a lot about a
  population periods of successful reproduction
  periods of high and low survival whether older
  individuals are being replaced whether a
  population is growing, declining, etc.

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Age Distribution and Stable Populations
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Age Distribution and Declining Populations
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A Dynamic Population in a Variable Climate
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Rates of Population Change Combining a Cohort
Life Table with a Fecundity Schedule

• Fecundity schedule - the tabulation of birth
  rates (the number of young born per female per
  unit time) for females of different ages in a
  population
• By combining the information in a fecundity
  schedule with data from a life table, we can
  estimate several important characteristics of a
  population

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Example A Population with Discrete Generations

• nx, the number of individuals in the population
  surviving to each age interval
• lx, survivorship, the proportion of the
  population surviving to each age x
• mx,average number of progeny produced by each
  individual in each age interval
• lx mx, the product of l and m
• Net reproductive rate, R0
• R0 ?lx mx
• To calculate the number of progeny produced by a
  population in a given time interval, multiply R0
  by the initial number of individuals in the
  population.

Example 2.4177 x 996 plants 2408
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Geometric Rate of Increase

• The ratio of population increase at two points in
  time ? Nt1
• n
• Where, Nt1 is the size of the population at a
  later time, and Nt is the size of the population
  at an earlier time

Example ? 2408 2.4177 996
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More on net reproductive rate

• R0 is an indication of the expected number of
  female offspring which a newly born female will
  produce during her life span
• Its an indication of whether a female replaces
  herself in the population
• R lt 1, the population will decline
• R 1, the population will remain constant
• R gt 1, population will increase (more offspring
  produced than needed to replace the female)

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Mean Generation Time (T)
T ? (x lx mx / Ro where x is
age Example from the common mud turtle These
turtles have an average generation time of 10.6
years 6.4/0.601 10.6
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per capita rate of increase (r)
r ln Ro / T Turtle example r ln (0.601)
/ 10.6 r -0.05