Chapter 9: Properties of Populations

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Lecture 6

• Chapter 9 Properties of Populations

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Learning Objectives

• Recognize
• 3 types of dispersion
• Contrast
• Dispersal vs. Migration
• 3 major age structures
• Define
• Dendrochronology

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Dispersal vs. Migration

• Both affect populations
• Dispersal movement of particular individuals to
  new habitat
• Usually involves young establishing own
  territories
• Migration movement of a WHOLE POPULATION to new
  habitat
• Usually involves a return trip

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Dispersal

• Movement into a population is immigration
• Think of i in
• Movement out of a population is emmigration
• Think of e exit

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Patterns of Dispersion

• Dispersion can be thought of as the product of
  dispersal

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Uniform Dispersion

• Typical of immense competion between individuals
• Desert plants competing for water
• Birds competing for nest sites

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Random Dispersion

• Position of each is independent of others
• Ex Perhaps the position of dandelion seeds

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Clumped Dispersion

• Very common occurs when resources are patchy
  (and they usually are)
• Animals at watering holes
• Poplar trees on creeks

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Dispersal of Yellow Poplar Seeds

• Like most plants, dispersal is passive
• Oaks dont ever disperse very far. Why?
• Other plants use animal dispersers
• Cherries
• Tomatoes

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Metapopulation

• A group made of many different populations
• Especially characteristic of modern, fragmented
  landscapes
• Dispersal occurs between populations (emmigration
  immigration)
• Can be an important source of genetic diversity
• Can boost populations that are failing

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Migrations

• Typically annual
• Gray whales
• Ring-necked ducks
• Can be daily
• Zooplankton in the ocean
• Once in lifetime
• Pacific salmon
• Some are unusual
• Monarch butterflies take three lifetimes

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Problem

• Density can vary, depending upon dispersion
• How do we deal with this?

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7th Inning Stretch
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Age Structure

• Many populations have 3 ecologically important
  age classes
• Prereproductive
• Reproductive
• Postreproductive

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Age Structures

• Stable
• Each person has one offspring!
• Typical of developed nations
• Declining
• Older populations tending to have lower birth
  rates
• Growing
• Characteristic of developing nations
• Hard on natural resources

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Age Pyramids
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Countries Compared
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Determining Age Structure of Animals

• Need to know age of each individual
• Teeth eruptions and wear pattern in deer
• USGS website
• Scale growth patterns of fish
• NPS website

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Tree Age Structure

• Each ring roughly one year
• Can be done by cutting down tree, or by taking
  small core sample
• The Bristlecone site
• Climate change site

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Tree Age Distributions

• Can be done by size class
• SD seedling
• SP sapling
• 8 cm classes
• By age
• Whats wrong with this oak population?