Population Dynamics

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Population Dynamics

• Factors influencing the expansion,
• decline or maintenance of
• populations
• A key to
• Preventing population declines
• Control of pest species
• Maintenance of important
• species

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Properties of Populations

• Before
• Distribution of species in space
• Movement among
• Distribution of individuals
• Abundance of individuals

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Properties of Populations

• Now
• Population structure
• Stable, expanding, or declining
• How will they change over time?

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Population Size
Population size
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Population Size

• To predict change
• Must know patterns of births
• Must know patterns of deaths
• Or patterns of survival

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Dispersal

• Can increase or decrease local population size
• Ongoing dispersal can join subpopulations to form
  a metapopulation
• Under studied

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Dispersal
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Patterns of Survival
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Patterns of Survival

• How do we estimate the likelihood of surviving to
  a certain age?
• Cohort life table
• Static life table
• Age distribution

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Cohort Life Table

• Cohort group of individuals born in the same
  time period
• Follow cohort until all die
• Historically accurate but not helpful for
  management

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Static Life Table

• Sample population at one point in time
• Generate age distribution
• Determine proportion of population at each age
  class
• Determine age at time of death
• Age skulls

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Aging Organisms
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Gray Squirrel Life Table
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Gray Squirrel Survivorship
Fairly constant chance of surviving from one year
to the next
1.0 0.1 0.01
0 1 2 3 4 5
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Bull Trout Survivorship
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Bull Trout Survivorship
1.0 0.1 0.01 0
Very high mortality among the young
0 1 2 3 4 5 6
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Dall Sheep Survivorship
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Dall Sheep
High survival among young
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Survivorship Curves
lx
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Survivorship Curves
Type I
Type II
Type III
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Survivorship Curves

• Type I
• High survival among young
• Low survival among old
• Humans other large vertebrates
• Some annual plants and inverts
• On shortened time scale

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Survivorship Curve

• Type II
• Nearly constant rate of survival
• Many birds, reptiles, small mammals, and plants

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Survivorship Curve

• Type III
• High mortality among young
• Marine fish
• Many trees, invertebrates

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Age Distribution

• One way to get static life table
• Also can suggest
• Population growing
• Population declining
• Population stable

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Age Distribution
Rapid growth Kenya
Post repro
Reproductives
Pre-reproductives
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Age Distribution
Slow growth United States
Post repro
Reproductives
Pre-reproductives
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Age Distribution
Zero growth Or Declining Italy
Post repro
Reproductives
Pre-reproductives
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Age Distributions
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Population Size

• To predict change
• Must know patterns of births
• Must know patterns of deaths
• Or patterns of survival

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Birth Rate

• Measures production of new individuals
• Seed production
• Eggs laid
• New shoots with vegetative repro
• Cell division for bacteria
• Babies born

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Birth Rate

• Usually changes with age
• Calculate average births per individual of each
  age
• mx
• For sexual species completely ignore males in
  life tables
• females and their daughters

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Gray Squirrel Birth Rate
How many babies does the average female squirrel
have in her lifetime?
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Gray Squirrel Production
Will this Population Increase, Decrease,
or Stay the same?
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Net Reproductive Rate

• R0 net reproductive rate
• R0 ?lxmx
• R0 1 -- population growing
• R0 population declining
• R0 1 -- no growth, replacement