Population Distribution

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Population Distribution Abundance
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Population

• Group of individuals of the same species
  inhabiting the same area

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Levels of Analysis

• Species range
• Large scale
• Distribution of populations within species range
• Movement of individuals among populations
• Small scale
• Distribution of individuals within populations

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Species Range

• Limited by physical environment

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Some species have large ranges
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Animals with Large Ranges
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Animals with Small Ranges
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Species Range

• Much environmental variation
• Wide vs. narrow tolerances
• Presence/absence of competing species

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Historical Range Changes
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Large Scale Population Distribution
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Large Scale Population Distribution

• Based on movement of individuals among
  populations
• Or likelihood of breeding with individuals of
  other populations

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Models of Population Structure
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Population Distribution Patterns

• Metapopulation
• Group of populations connected by movement of
  individuals
• Individual populations are born (colonized) and
  die (go extinct)

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Small Scale Individual Distribution

• Within populations individuals can be distributed
• Randomly, Regularly, Clumped
• Determined by interactions between individuals
  environmental structure

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Random Distribution

• Location of each individual independent of others
• Neutral interactions
• Uniform resources

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Regular Distribution

• Individuals evenly spaced
• Further apart than expected by chance
• Antagonistic interactions
• Uniform resources

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Clumped Distribution

• Individuals closer together than expected by
  chance
• Patchy resources
• Attraction of individuals

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Clumped Distributions
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(No Transcript)
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Males arent clumped--regularly distributed
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Population Density

• Density individuals per unit of space
• Abundance individuals

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Measuring Density

• Crude density individuals per unit of space
  (favorable and unfavorable)
• Ecological density individuals per unit of
  available living space (favorable)

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Spotted Owls

• Crude density
• 0.65 / 400 ha
• Ecological density
• 1.71 / 400 ha mature or old growth forest
• 4.8 / 400 ha old growth forest

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Measuring Density

• Whats an individual?
• Many species reproduce asexually
• Many can reproduce both sexually and asexually
• If genetically identical are they individuals?
• Unitary vs. modular organisms

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Individuals?

• Quaking aspen
• Vegetative reproduction
• Oldest clone
• 80,000 yrs
• 47,000 trees
• Genet-individual from sexual reproduction
• Ramet-individual from asexual reproduction

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Modular Organisms
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Measuring Density

• Census count everything
• Estimate
• Quadrat sampling
• Good for sessile organisms
• Mark-recapture
• Good for mobile organisms

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Density Changes Over Time

• Crop damage caused by chinch bugs
• Yellow low densities
• Blue high densities

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Mark-recapture

• Basics
• Trap and mark
• Trap again
• Compare number of recaptures to new captures
• Estimate pop size

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Single Mark-recapture

• Initial phase
• Trap, mark, release
• M marked released
• Second phase
• Trap again
• n trapped in second phase
• R recaptured
• N nM/R
• N pop size

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Mark-recapture Example

• Capture mark 39 rabbits
• Repeat effort
• Capture 34 rabbits
• 15 with tags
• 19 unmarked
• NnM/R
• N34(39)/15
• N88
• N Estimate!

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Quadrat Sampling

• Set up plots of pre-determined size
• Estimate
• species
• individuals of each species
• of area covered by species

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Size vs. Density
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Rarity and Vulnerability