Population Distribution

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Chapter 9

• Population Distribution
• and Abundance

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Climate and Distribution
Species distribution is based on climate at large
scales Often, related species segregate
spatially based on climatic differences
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Climate and Distribution
Climate is influenced by many factors and can
result in unusually shaped range maps
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Ecological Niche
Across wide distributions, many species are
adapted to a specific climate
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Temperature-Moisture Gradient
Species segregate on smaller scales based on
physical properties of the environment such as
temperature and moisture
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Light Absorption
Pubescence on leaves prevents overheating and
reduces light absorption in Encelia
farinosa Encila frutescens keeps cool by
transpiring water
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Microenvironment and Distribution
Encila frutescens can afford to stay cool using
transpiration because it inhabits the moistest
microclimates of the area
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Distribution Patterns
Species can exist within their ranges in clumped,
regular, or random patterns
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Causes of Distribution Patterns
Distribution patterns can be influenced by
interactions among individuals, permitting
greater space for more aggressive species
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Changes in Distribution Patterns
Distribution patterns can change as populations
and individuals mature
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Large Scale Distribution Patterns
Populations tend to exhibit clumped distributions
at large scales
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Community Continuums
Observing clumping by populations within a
community allows for the isolation of continuums
along which species are abundant and then less
abundant. Largely based on physical properties
of the environment
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Distribution and Body Mass
Mammal density decreases with increasing body size
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Distribution and Body Size
Decreasing density with increasing body size
holds true for many groups of animals
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Distribution and Plant Size
Plant density also decreases with increasing
adult size Densities of juvenile individuals can
be much greater than that of adults
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Summary

• The physical environment limits the distribution
  of species
• Small scale distributions can be clumped,
  regular, or random
• On larger scales, populations are clumped
• Density decreases with increasing organism size
• Rarity is influenced by geographic range, habitat
  tolerance, and population size
• Rare species are vulnerable to extinction