IB 153 Alternate Stable States and
Maintenance of Species Diversity
Alternate Stable States
Can there be more than one stable
community composition in a given habitat?
Classical succession theory assumes that the changes
in community structure following a disturbance follow a
repeatable sequence that ends in a single, selfreplacing, climax state
Lewontin (1969) suggested that during the course of
community development, “pulse” perturbations might
shift the same assemblage of species into alternate
stable states under the same environmental conditions.
The states might then maintained by positive
feedbacks (e.g. adults create environmental conditions
that favor their own offspring)
11/7/2006
• Alternative stable states (the
community perspective)
– Parameters are constant
– “State” variables change
– Different community states
result from:
• Differential recruitment or
initial conditions (“history
matters”)
• An acute perturbation
sufficiently large
to move the
system to a new
(local) basin of
attraction
• Regime shifts (the ecosystem
perspective)
– “State” variables are constant
– Parameters change through
time
– Different regimes are caused
by:
• New interactions among state
variables
• A chronic (directional)
perturbation to the
system changes the
landscape of the
attractor(s)
Figure from Beisner et al.
(2003) Frontiers Ecol.
Env. 1: 376-382
Minimum criteria for demonstrating the existence
of multiple stable states
1. States must be shown to occur in the same
environment
2. Disturbance or experimental manipulation
must be a “pulse” (one-time) perturbation
3. Observations or experiments must be carried
out over a sufficiently long time and over a large
enough area to ensure that the alternative states
are self-sustaining
Nonequilibrium theories
1.
2.
3.
Intermediate disturbance hypothesis
Equal chance hypothesis
Gradual change hypothesis
Shortcoming of most
Alternative Stable State examples
1. Evidence is inapplicable since physical
environment is different in the alternative
states
2. One or both states persist only when artificial
controls are applied
3. Evidence is simply inadequate (e.g. records
not sufficient to demonstrate turnover of
component populations)
Equilibrium hypotheses
4.
5.
6.
Niche diversification
Circular networks
Compensatory mortality
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IB 153 Alternate Stable States and
Maintenance of Species Diversity
11/7/2006
Intermediate disturbance hypothesis
Heron Island, Great Barrier Reef, Australia
Equal chance hypothesis
An intermediate rate of
disturbance maintains diversity
Force to
move
boulder (N)
Surface area
(cm2)
Mean percent
disturbed / mo
Mean species
richness
Mean
eH’
eH’
= 49
= 139
42
1.7
1.5
0.41
50 - 294
144 - 1364
9
3.8
2.5
1.05
> 294
> 1364
0.1
2.9
1.6
0.40
Variance
Peter Sale
1. Species have very similar resource requirements
2. Species have very similar life history characteristics
(recruitment and longevity)
3. “First-come, first-served” competitive interactions (first
individual to occupy space, holds it until it dies)
4. Recruitment rates not tied to local adult abundance
(long-distance dispersal of larvae or seeds)
Gradual change hypothesis
(Hutchinson 1961, Paradox of the Plankton)
Niche diversification hypothesis
Hypothesis developed to explain the
“paradox” of multiple phytoplankton species
coexisting in an apparently homogeneous
environment (water column of a lake)
If the competitive abilities of the species
differ with environmental conditions, and
such conditions shift back-and-forth at a rate
that is faster than the rate of competitive
exclusion, the species can coexist (e.g.
seasonal turnover in lakes).
Diversity increases with:
• More kinds of resources
• More specialization
• Greater allowable overlap
2
IB 153 Alternate Stable States and
Maintenance of Species Diversity
Compensatory mortality hypothesis
(Selective consumption of dominant competitor)
Circular networks hypothesis
(Buss and Jackson 1979)
11/7/2006
The Janzen-Connell hypothesis for
maintenance of rain forest diversity
Networks in crytpic coral reef communities
Usually assume interpecific interactions to be
transitive (A > B > C, and A > C)
But they may sometimes be non-transitive or circular
(A > B > C, but C > A). May occur when
mechanisms of competition differ among species
pairs, especially in interphyletic interactions
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