COMMUNITY STRUCTURE cpt. 20

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• COMMUNITY STRUCTURE (cpt. 20)
• Biological structure
• composition and abundance
• temporal changes (succession)
• relationships between species
• (interactions, dominance, Keystones etc.)

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• COMMUNITY STRUCTURE (cpt. 20)
• Biological structure determines how
• the community functions
• Productivity
• Trophic levels
• Nutrient cycling etc.

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• VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURE
•  
• LIFE FORMS
• HORIZONTAL STRUCTURE
• VERTICAL STRUCTURE

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LIFE FORMS In the 1920s, a Danish botanist,
Raunkiaer, provided a classification (1934) based
on the position of the perennating tissue (buds,
bulbs, seeds etc.).   This can be used to
characterize a community because certain life
forms are dominant in certain environments.
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RAUNKIAERS LIFE FORMS
Phanerophytes (trees)
Hemicryptophytes (perennial herbs)
Therophytes (annuals)
Cryptophytes (bulbs etc.)
Chamaephytes (shrubs)
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• The great biomes of the world show a remarkable
  degree of convergence in their physical
  appearance, despite wide variation in the
  species involved.
•  
• It is difficult to distinguish between
• chaparral of California and Chile
• nutrient-poor heaths of S. Africa and Australia
• Arctic and Antarctic fell fields
• rain forest in Brazil and SE Asia
•  
• These divergences are vivid testimony of the
  importance of climatic factors as agents of
  natural selection.

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LIFE FORMS IN DIFFERENT BIOMES
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• SEVERAL POINTS EMERGE FROM THESE COMPARISONS
• Where there is no unfavorable season, or the less
  favorable is not too severe, then tree-like
  plants (phanerophytes) predominate in the flora
  as a whole.
• Under ideal growth conditions (constant warmth
  and moisture) trees are dominant, simply because
  the competitive spoils go to the tallest
  individuals.
• In less equable climates, trees may still be the
  dominant plants in most communities, but the
  flora as a whole is made up predominantly of
  other life forms (hemicryptophytes in northern
  temperate latitudes)

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  Where the summer is arid (as in deserts and
Mediterranean climates), there is a preponderance
of annual plants (which avoid drought by passing
the dry period as dormant seeds) and geophytes
(which avoid drought by die-back of their
above-ground parts and survive by means of
underground storage organs). Other desert plants
that tolerate drought may appear to be dominant
if the vegetation is surveyed during the dry
season (xerophytic shrubs and stem succulents)  

• Where the summer is arid (as in deserts and
  Mediterranean climates), there is a preponderance
  of annual plants (which avoid drought by passing
  the dry period as dormant seeds) and geophytes
  (which avoid drought by die-back of their
  above-ground parts and survive by means of
  underground storage organs). Other desert plants
  that tolerate drought may appear to be dominant
  if the vegetation is surveyed during the dry
  season (xerophytic shrubs and stem succulents)

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5. Where extreme cold and exposure characterize
the unfavorable season, there is a shift towards
cushion-forming plants and other species whose
buds are held close to the ground surface
(chamaephytes). Many Arctic plants have their
perennating buds protected by the dead leaf-bases
of last year's shoots, because both the exposed
aerial environment and the frozen soil are
extremely inhospitable conditions for bud
survival.
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• VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURE
•  
• LIFE FORMS
• HORIZONTAL STRUCTURE
• VERTICAL STRUCTURE

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• HORIZONTAL STRUCTURE
• Random
• Probably never occurs
• Regular or Systematic
• Plantations of crops
• Behavioural interactions
• Aggregated or Clumped

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RANDOM ARRANGEMENT
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• HORIZONTAL STRUCTURE
• Random
• Probably never occurs
• Regular or Systematic
• Plantations of crops
• Behavioural interactions
• Aggregated or Clumped

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REGULAR OR SYSTEMATIC ARRANGEMENT
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REGULAR, OR SYSTEMATIC, ARRANGEMENT
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• HORIZONTAL STRUCTURE
• Random
• Probably never occurs
• Regular or Systematic
• Plantations of crops
• Behavioural interactions
• Aggregated or Clumped

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• AGGREGATED
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions

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• AGGREGATED
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions

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• AGGREGATED
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions

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Solidago canadensis
Solidago nemoralis
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Buttercup (Ranunculus sp.)
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BullrushCattail
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Krebs Fig. 7.9 p94,95,137
Chthamalus
Balanus
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• VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURE
•  
• LIFE FORMS
• HORIZONTAL STRUCTURE
• VERTICAL STRUCTURE

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• VERTICAL STRUCTURE
• Forest (usually associated with light
  diminution)
• Warblers in a coniferous forest
• Aquatic systems
• Soil layers
• Root systems

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WARBLERS
(Krebs Fig. 12.15 p193)
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(Krebs Fig. 12.15 p193)
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