The deadly couch

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The deadly couch cobra -- coiled and alert in
its natural habitat
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Ecosystems, communities relationships

• Ecosystems abiotic biotic, still is somewhat
  abstract to most of us
• Community or Biotic Community the biotic
  portion of the ecosystem and less abstract
• Examples cypress dome, strand (think Student
  Union), pine flatwoods, tundra, coral reefs

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Community is context of critter relationships

• Predation, competition, facilitation, parasitism,
  succession, population growth, extinctions,
  evolution, and more.
• Ecosystem processes tend to be less watched here
  with more emphasis on species

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Scale is important in thinking about biotic
communities

• Space biomes, landscape, community
• Time geologic, historic, yearly, daily
• Change is the rule, change happens

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Community Attributes

• Species diversity
• Relative abundance
• Species dominance
• Growth form and structure or physiognomy

• Community classification
• Succession

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• Classification of Communities in Landscapes
• Biomes are very large scale units that are
  comprised of similar community types
• Community represents a smaller scale unit of
  organization which is considered to be a
  fundamental unit of a landscape
• Are communities real?
• If real, they should be discrete and
  discontinuous
• If imaginary, they should be non-discrete and
  continuous

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• Wetlands of Seminole County
• Deep Marsh
• Shallow Marsh
• Bayhead Swamp
• Wet Prairie
• Hydric Hammock
• Cypress Swamp
• Mixed Hardwood Swamp

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• Two schools of thought on communities
• Association -vs- Continuum school
• Association concept leads to a classification of
  communities
• A community is thought to be of a definite
  composition, presenting a uniform physiognomy and
  growing under uniform habitat conditions
• Continuum concept does not emphasize community
  classification
• It relates community distributions to
  environmental gradients

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• In practical terms, an association is defined on
  the basis of its floristic composition
• 1. Series of stands are studied
• 2. Plant species lists are summarized trees,
  shrubs, herbs
• 3. Stands that share the same dominants are
  grouped
• 4. Stands are real, the association is an
  abstraction
• 5. Stands may be collectively grouped based on
  similarities
• 6. Name usually is from dominants (Oak-hickory,
  longleaf pine-turkey oak, beech-maple)

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Associations repeat themselves in space and time
N-facing slope
S-facing slope
N-facing slope
S-facing slope
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Vegetation Zonation
Marsh/Mangrove Zone Scrub Zone
Forest Zone
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Optimal Conditions
High
Species Abundance
Low Tolerance
Low Tolerance
Low
Low High
Environmental Variable
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• Examples of Environmental Gradients
• Temperature
• Soil Characteristics
• e.g., moisture
• pH ,
• texture,
• nutrients,
• toxic substances (e.g., salt)
• Light
• Frequency of disturbance regimes
• e.g., flood zones (hydroperiod)

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A) Association concept
B
C
A
D
Importance Value
B) Continuum concept
C
A
B
D
Environmental Gradient
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A) Association concept
A
B
C
D
Environmental Variable
B) Continuum concept
A
B
C
D
Distance along Environmental Gradient
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• Direct Gradient Analysis
• Look at continuous variation of vegetation in
  relation to environmental factors
• J. Curtis - Vegetation of Wisconsin
• R. Whittaker - Vegetation of Smoky Mountains
• Altitude subsumes a host of correlated factors,
  e.g.,
• heat
• rainfall
• wind - drying power
• snowfall

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Dry, Southfacing Slopes in Great Smoky Mountains
Virginia Pine Pitch Pine Table-Mountain Pine
80 60 40 20 0
Percentage of Stand
1500 2500
3500 4500
Elevation (ft.)
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Whittakers Findings
Importance Value
Environmental Gradient

• Bell-shaped distributions
• No sharp transitions divide communities
• Individualistic distributions are tied to
  environmental conditions
• Vegetation exists as a continuum
• Discrete units are imagined by the investigator

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Abundance of Clam Species in Monkey Mia, Australia
Average Number/m2
Mean Low Tide
Relative Elevation (cm)
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• Biome
• ?
• Landscapes
• ?
• Communities
• Real, Discrete Imagined, continuous
• ? ?
• Plant association Vegetation as a
  continuum
• ? ?
• 1. Classification 1. Identifies habitat
  mosaic
• 2. Map distribution 2. Identifies dominants
  in relation to habitat features
• 3. Dominants, Species list 3. Emphasizes
  individual distributions and
  environmental gradients