Community%20Attributes

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Community Attributes

• Kenneth M. Klemow, Ph.D.
• Wilkes University

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Communities defined

• Assemblage of interacting populations in an area.
• Typically categorized according to trophic level
  / functional group
• Size of communities varies
• Depends on size of species and degree of mobility
• For vegetation, concept of stand important
• Have important attributes

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Species composition

• List of species in an area.
• Can range from monocultures to assemblages of
  hundreds of species.
• Floras and faunas

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Species area curve

• Look at accumulation of species with increasing
  number of plots sampled
• Get saturation effect
• Used in conservation biology to predict species
  loss with habitat loss

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Density

• Number of individuals in an area
• Each broad taxonomic group presents own
  challenges
• Plants - ramets vs genets
• Animals - deal with mobility
• Fungi - Whats an individual?
• Calculate relative density

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Calculating relative density
Species Density Rel. Dens.
A 400 37.0
B 60 5.6
C 370 34.3
D 80 7.4
E 170 15.7
Total 1080 100.0
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Frequency

• Proportion of times that a species will appear in
  a defined number of samples.

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Species Frequency Rel. Freq.




Total 10
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Concepts relating to frequency

• Commonness vs rarity
• Common gt60
• Rare lt20
• Raunkiaers law
• A 0-20
• B 20-40
• C 40-60
• D 60-80
• E 80-100
• AgtBgtCDltE

A
B
C
D
E
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Abundance patterns in communities

• Counts of species abundance or frequencies often
  yield interesting patterns.

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Now sort the data

• Order of decreasing abundance

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And categorize to yield frequency distribution

• Place into categories of 25

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Now create a histogram
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Now set up categories to follow geometric
progression

• 0-1
• 1-2
• 2-4
• 4-8
• 8-16
• 16-32
• 32-64
• 64-128
• 128-256

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Now create a new histogram
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Ecologists have found lognormal distribution in
nature
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Diversity

• Measure of heterogeneity among species in a
  community
• Has two components
• Richness
• Evenness

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Measures of Diversity

• Species richness - S
• Shannon-Weiner index
• H -?(pi x ln pi)
• Accounts for both richness and evenness
• Evenness
• J H/ln S
• Simpsons index
• ?(pi)
• Accounts for dominance
• Inverse Simpsons index
• 1/ ?(pi)
• Accounts for diversity

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Look more closely at Shannon-Weiner index
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Stress-subsidy relationships important
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???????? diversity

• ? diversity - within specific community or
  habitat
• ? diversity - across several communities along a
  gradient
• ? diversity - across range of habitats in
  landscape or geographic area

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Dominance

• Degree to which one species intercepts resources
  and regulates community function
• Typically related to biomass
• Concept of keystone species

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Stability

• Ability of a community to remain constant over
  time, especially in face of perturbation.
• Two components
• Resistance
• Resilience