COMMUNITY CHANGE (SUCCESSION)

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COMMUNITY CHANGE (SUCCESSION)

• Krebs cpt. 21 pages 403-424 431

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• Connell and Slatyer 1977
• Succession driven by interactions between
  species
• FACILITATION
• TOLERANCE (COMPETITION)
• INHIBITION

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SUCCESSION PATHWAYS
A
B
C
D
Facilitation
Tolerance Inhibition
A
B
D
C
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Succession models (Krebs 5th Fig. 21.4)
Species interactions
- o
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FACILITATION only certain pioneer species can
establish after disturbance. Early species
enhance the ability of later species to establish.
INHIBITION any species can invade. Once
established, species resist further invasion and
are displaced only by death or further
disturbance.
TOLERANCE any species can invade. Early species
have little or no effect on abilities of later
species to invade. Later species can displace
early species by reducing resources to levels
below those tolerated by earlier occupants.
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A study from abandoned farmland illustrates some
aspects of Facilitation, Tolerance and Inhibition
(see Krebs pp 419-422)

• FIELD ABANDONED IN FALL
• 1. INITIAL INVASION
• Horseweed
• a winter annual
• produces abundant seed
• self-allelopathic

Conyza canadensis
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• 2. NEXT SEASON
• Asters
• More susceptible to decaying roots of horseweed,
  than horseweed
• Tolerant of dry conditions

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• 3. SECOND AND THIRD SEASONS
• Bluestem
• Seedlings invading since initial abandonment
• Broomsedge
• Seedlings invading since initial abandonment
• More tolerant of dry conditions than Asters
• Decaying roots of Horseweed promote growth

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Bluestem
Broomsedge
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SUMMARY

• FACILITATION
• Broomsedge is promoted by decaying roots of
  horseweed aster
• TOLERANCE
• Broomsedge displaces aster through competition
  for water
• INHIBITION
• Horseweed litter prevents aster from persisting

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FORCIER 1975 Succession driven by interaction
of disturbance life history traits of species

• Studied trees in a New Hampshire forest
• Trees with dbh gt2 cm (400 plots)
• 90 of canopy
• Sugar maple
• American beech
• Yellow birch

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Eastern deciduous hardwood forests Several tree
species
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Grey Birch, Betula populifera
Black Gum, Nyssa sylvatica
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Beech, Fagus sylvatica
Red Maple, Acer rubrum
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SUGAR MAPLE
YELLOW BIRCH
BEECH
r K
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SPECIES Density (/m2) (dmin/dmax ) x 100 plots with at least 1 seedling Mass/ind (mg)
Yellow birch 21.3 2 92 8
Sugar maple 10 57 73 268
Beech 3.9 66 55 569
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Number of cohort alive at beginning of interval Number of cohort alive at beginning of interval Number of cohort alive at beginning of interval
Age interval Yellow birch Sugar maple Beech
0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 1000 70 lt30 1000 583 317 225 166 118 84 54 48 42 1000 410 262 188 138 121 110 92 87 83
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CANOPY SEEDLINGS SEEDLINGS SAPLINGS
lt 0.5m tall lt 0.5m tall 0.5 2 m tall
Yellow birch Yellow birch Sugar maple Beech 0 - -
Sugar maple Yellow birch Sugar maple Beech 0 0 0
Beech Yellow birch Sugar maple Beech 0 0 0 0 Sprouts (seeds -)
significantly present 0 no relation -
significantly absent
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CLIMAX MICROSUCCESSION
Beech (seed)
Beech (sprouts)
MINOR DISTURBANCE
Sugar Maple
Yellow birch
CATASTROPHIC DISTURBANCE
Successional communities