Community ecology

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Community ecology

• Outline
• Community structure attributes
• Factors influencing the structure of communities
• Community dynamics
• Chapter 16-18

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Community attributes

• of species
• Relative abundance of species
• Nature of species interactions (food webs)
• Physical structure

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Community structure

• Species richness ( of species within community)

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Community structure

• Relative abundance ( each species contributes to
  the total number of individuals)

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Stand one
Stand two
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Simpsons diversity index

• D 0 - 1
• 0 high diversity
• 1 low diversity
• Stand one (Table 16.1) D0.13
• Stand two (Table 16.2) D0.36

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Dominance
Yellow-poplar
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Food webs
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Keystone species
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Functional groups

• Feeding level
• Exploitation of common resources (guilds)
• Photosynthetic pathway
• Shade tolerance
• Life history

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Physical structure
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Zonation
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supratidal
intertidal
subtidal
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Association

• Relatively consistent species composition
• Uniform general appearance
• Distribution that is characteristic of a
  particular habitat

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Organismic concept of communities
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Continuum concept of communities
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Factors controlling community structure
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Fundamental niche
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Species interactions
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Keystone predation
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Apparent competition
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Indirect commensalism
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Top-down vs. bottom-up control
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The number of trophic levels regulates plant,
herbivore and carnivore numbers
trophic levels
B/comp numbers limited by availability of
resources (bottom-up regulation). Competition
strong, predation weak. T/pred numbers limited
by predation (top-down regulation). Competition
weak, predation strong.
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Stress tolerance and competition
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Black needle rush
Salt meadow cordgrass
Smooth cordgrass
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Environmental heterogeneity
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Relationship between the number of plants per
300m2 plot beside the hood river, NWT, and an
index (ranging from 0 to 1) of spatial
heterogeneity in abiotic factors associated with
topography and soil. More spatially
heterogeneous plots had higher species richness.
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Environmental quality
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Plant species diversity in a control plot and a
fertilized plot in the Parkgrass experiment in
Rothamstead, England. Fertilized plots have
lower species diversity. The Parkgrass
experiment, which began in 1856, is the longest
running ecological experiment.
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Community stability

• Types of stability
• Resilient community returns to former state
  after disturbance
• Resistant community changes little in response
  to disturbance

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Community dynamics Succession
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Primary succession
Pioneer species
Late successional species
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Secondary succession
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beach grass
shrubs
pines
oak
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Primary succession newly exposed substrate
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Dryas sp.
An early succession species on glacial moraines
in Glacier bay. Dryas is a symbiotic N-fixing
plant
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Salix arctica
Populus trichocarpa
After Dryas, cottonwood and willows become
established
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Alnus incana
Alders become the dominant tree after 50 years
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Climax mixed spruce-hemlock forest
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Secondary succession after disturbance
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Autogenic vs. allogenic change
Density
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Allogenic environmental change
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Species diversity during succession
Oak-pine forest
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Intermediate disturbance hypothesis
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Intermediate disturbance hypothesis
High
Low
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In New Zealand streams, less disturbed sites
support more complex communities (i.e.,
communities with larger, more connected food webs)
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Succession of heterotrophs
Bark beetle/wood-boring beetle
Invertebrates/mice/salamanders
Predatory insects
Moss and lichen
Fungi/bacteria
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Changes over geologic time
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Concept of community revisited
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Concept of community revisited
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