Transcript Document

COMMUNITY CHANGE
(SUCCESSION)
Krebs cpt. 21; pages 403-424; 431
Connell and Slatyer 1977
Succession driven by interactions
between species:

FACILITATION

TOLERANCE (COMPETITION)

INHIBITION
SUCCESSION PATHWAYS
Facilitation
A
B
C
Tolerance & Inhibition
A
B
D
C
D
Succession models (Krebs 5th Fig. 21.4)
Species interactions
+-o
+
+
+
+
+
-
+
-
o
o
o
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.
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
2. NEXT SEASON:
• Asters
• More susceptible to
decaying roots of
horseweed, than horseweed
• Tolerant of dry conditions
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
Bluestem
Broomsedge
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
FORCIER 1975
Succession driven by interaction of
disturbance & life history traits of species
Studied trees in a New Hampshire forest
• Trees with dbh >2 cm (400 plots)
• 90% of canopy:
• Sugar maple
• American beech
• Yellow birch
Eastern deciduous
hardwood forests
Several tree
species
Grey Birch, Betula populifera
Black Gum, Nyssa sylvatica
Beech, Fagus sylvatica
Red Maple, Acer rubrum
YELLOW
BIRCH
r
SUGAR
MAPLE
BEECH
K
Many small offspring (r-type)
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
Beech
3.9
SPECIES
Variable density and high dispersal
57
73
268
More even density and lower dispersal
66
55
Fewer large offspring (K-type)
569
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
<30
1000
583
317
225
166
118
84
54
48
42
1000
410
262
188
138
121
110
92
87
83
CANOPY
SEEDLINGS
< 0.5m tall
SAPLINGS
0.5 – 2 m tall
Yellow birch Yellow birch
Sugar maple
Beech
+
+
0
+
-
Sugar maple Yellow birch
Sugar maple
Beech
Beech
Yellow birch
Sugar maple
Beech
0
+
+
0
0
+
0
0
++
0
0
Sprouts + (seeds -)
+ = significantly present
0 = no relation
- = significantly absent
Beech
(sprouts)
Beech
(seed)
MINOR
DISTURBANCE
Sugar
Maple
Yellow
birch
Successional
communities
CATASTROPHIC
DISTURBANCE