Biol 302 Introduction1 COMMUNITY STRUCTURE (cpt. 20) Biological structure: composition and abundance temporal changes (succession) relationships between.

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.)

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COMMUNITY STRUCTURE (cpt. 20)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 VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:

1. LIFE FORMS

2. HORIZONTAL STRUCTURE

3. VERTICAL STRUCTURE

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VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:

1. LIFE FORMS

2. HORIZONTAL STRUCTURE

3. VERTICAL STRUCTURE

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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.

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Christen C. Raunkiaer 1860-1938

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RAUNKIAER’S LIFE FORMSRAUNKIAER’S LIFE FORMS

Phanerophytes (trees)

Chamaephytes (shrubs)

Hemicryptophytes (perennial herbs)

Cryptophytes (bulbs etc.)

Therophytes (annuals)

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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 BIOMESLIFE FORMS IN DIFFERENT BIOMES

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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

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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

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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)

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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)

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)

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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 VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:

1. LIFE FORMS

2. HORIZONTAL STRUCTURE

3. VERTICAL STRUCTURE

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HORIZONTAL STRUCTUREHORIZONTAL STRUCTURE:

1. Random

• Probably never occurs

2. Regular or Systematic

• Plantations of crops

• Behavioural interactions

3. Aggregated or Clumped

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HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:

1. Random

• Probably never occurs

2. Regular or Systematic

• Plantations of crops

• Behavioural interactions

3. Aggregated or Clumped

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RANDOM ARRANGEMENTRANDOM ARRANGEMENT

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HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:

1. Random

• Probably never occurs

2. Regular or Systematic

• Plantations of crops

• Behavioural interactions

3. Aggregated or Clumped

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REGULAR REGULAR

[OR SYSTEMATIC][OR SYSTEMATIC]

ARRANGEMENTARRANGEMENT

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REGULAR, OR SYSTEMATIC, ARRANGEMENTREGULAR, OR SYSTEMATIC, ARRANGEMENT

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HORIZONTAL STRUCTURE:HORIZONTAL STRUCTURE:

1. Random

• Probably never occurs

2. Regular or Systematic

• Plantations of crops

• Behavioural interactions

3. Aggregated or Clumped

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AGGREGATED:AGGREGATED:

• ants and termites

• fish and phytoplankton

• plants

• distribution from parent

• environmental heterogeneity

• species interactions

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AGGREGATED:AGGREGATED:

• ants and termites

• fish and phytoplankton

• plants

• distribution from parent

• environmental heterogeneity

• species interactions

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AGGREGATED: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; p94,95,137Chthamalus

Balanus

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VARIOUS WAYS TO DESCRIBE VARIOUS WAYS TO DESCRIBE COMMUNITY STRUCTURECOMMUNITY STRUCTURE:

1. LIFE FORMS

2. HORIZONTAL STRUCTURE

3. VERTICAL STRUCTURE

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VERTICAL STRUCTURE: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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