biol 302 introduction1 community structure (cpt. 20) biological structure: composition and abundance...
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Biol 302 Introduction 1
COMMUNITY STRUCTURE (cpt. 20)COMMUNITY STRUCTURE (cpt. 20)
Biological structure:
• composition and abundance
• temporal changes (succession)
• relationships between species
• (interactions, dominance, Keystone’s etc.)
Biol 302 Introduction 2
COMMUNITY STRUCTURE (cpt. 20)COMMUNITY STRUCTURE (cpt. 20)
Biological structure determines how
the community functions:
• Productivity
• Trophic levels
• Nutrient cycling etc.
Biol 302 Introduction 3
VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:
1. LIFE FORMS
2. HORIZONTAL STRUCTURE
3. VERTICAL STRUCTURE
Biol 302 Introduction 4
VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:
1. LIFE FORMS
2. HORIZONTAL STRUCTURE
3. VERTICAL STRUCTURE
Biol 302 Introduction 5
LIFE FORMS
In the 1920’s, 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.
Biol 302 Introduction 7
RAUNKIAER’S LIFE FORMSRAUNKIAER’S LIFE FORMS
Phanerophytes (trees)
Chamaephytes (shrubs)
Hemicryptophytes (perennial herbs)
Cryptophytes (bulbs etc.)
Therophytes (annuals)
Biol 302 Introduction 13
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.
Biol 302 Introduction 15
Phanerophytes (trees)
Chamaephytes
(shrubs)
Hemicryptophytes
(perennial herbs)
Cryptophytes (bulbs etc.)
Thero
phytes (annuals)
World or NormalWorld or Normal 4646 99 2626 66 1313
LATITUDE
Tropical rain forest 96 2 2
Sub tropical forest 65 17 2 5 10
Warm temperate forest 54 9 24 9 4
Cold temperature forest
10 17 54 12 7
Tundra 1 22 60 15 2
Biol 302 Introduction 16
Phanerophytes (trees)
Chamaephytes
(shrubs)
Hemicryptophytes
(perennial herbs)
Cryptophytes (bulbs etc.)
Thero
phytes (annuals)
World or NormalWorld or Normal 4646 99 2626 66 1313
MOISTURE
Mesophytic forest 34 8 33 23 2
Oak woodland 30 23 36 5 6
Dry grassland 1 12 63 10 14
Semi-desert 59 14 27
Desert 4 17 6 73
Biol 302 Introduction 17
SEVERAL POINTS EMERGE FROM THESE COMPARISONSSEVERAL POINTS EMERGE FROM THESE COMPARISONS:
1. 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.
2. Under ideal growth conditions (constant warmth and moisture) trees are dominant, simply because the competitive spoils go to the tallest individuals.
3. 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)
Biol 302 Introduction 18
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)
4. 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)
Biol 302 Introduction 19
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.
Biol 302 Introduction 20
VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:
1. LIFE FORMS
2. HORIZONTAL STRUCTURE
3. VERTICAL STRUCTURE
Biol 302 Introduction 21
HORIZONTAL STRUCTUREHORIZONTAL STRUCTURE:
1. Random
• Probably never occurs
2. Regular or Systematic
• Plantations of crops
• Behavioural interactions
3. Aggregated or Clumped
Biol 302 Introduction 22
HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:
1. Random
• Probably never occurs
2. Regular or Systematic
• Plantations of crops
• Behavioural interactions
3. Aggregated or Clumped
Biol 302 Introduction 24
HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:
1. Random
• Probably never occurs
2. Regular or Systematic
• Plantations of crops
• Behavioural interactions
3. Aggregated or Clumped
Biol 302 Introduction 25
REGULAR REGULAR
[OR SYSTEMATIC][OR SYSTEMATIC]
ARRANGEMENTARRANGEMENT
Biol 302 Introduction 27
HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:
1. Random
• Probably never occurs
2. Regular or Systematic
• Plantations of crops
• Behavioural interactions
3. Aggregated or Clumped
Biol 302 Introduction 28
AGGREGATED:AGGREGATED:
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions
Biol 302 Introduction 29
AGGREGATED:AGGREGATED:
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions
Biol 302 Introduction 30
AGGREGATED:AGGREGATED:
• ants and termites
• fish and phytoplankton
• plants
• distribution from parent
• environmental heterogeneity
• species interactions
Biol 302 Introduction 35
VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:
1. LIFE FORMS
2. HORIZONTAL STRUCTURE
3. VERTICAL STRUCTURE
Biol 302 Introduction 36
VERTICAL STRUCTURE:VERTICAL STRUCTURE:
• Forest (usually associated with light diminution)
• Warblers in a coniferous forest
• Aquatic systems
• Soil layers
• Root systems