Transcript Community Development

Community Development
and Species-Area
Relationships
BIOL400
2 November 2015
Community
Development:
Ecological
Succession
Primary vs. Secondary Succession
 Primary

succession occurs on bare soil
Ex: Mt. Saint Helens
 Secondary
succession follows
disturbance in areas having some
vegetation already

Ex: Old-field succession
Figs. 18.10—18.12 pp. 366-67
Clements’ View of Succession

Community-asSuperorganism Concept
• aka Relay Floristics Model


Seres (= successional
stages) analogous to
developmental stages of
an organism
Monoclimax: single,
predictable climax
community (the
community that remains
stable, ending
succession)
Fig. 18.5 p. 358
Egler's Initial Floristic
Composition Model
 Much

more individualistic
Contingency: what plant species happen to
colonize first will greatly influence both the
sequence and the climax
 Inhibition
of earlier stages by later stages
Connell and Slatyer's Facilitation,
Inhibition, and Tolerance Model
drives Clements’ relay
floristics model
 Facilitation
• A modifies environment favorably for B, etc.
drives Egler’s initial floristic
composition model
 Inhibition
• B suppresses growth of A, etc.
 Tolerance
refers to the ability of a species
at any one stage to tolerate…
• …resource levels (important early in sequence)
• …level of competition for soil nutrients and light
(important later in sequence)
Succession and
Plant Life Histories
 Whether
a species predominates in early
vs. late succession tends to correlate with
features of its ecology and life history


Ability to colonize
Ability to tolerate competition with other
species
Table 18.1
p. 359
Fig. 18.7 p. 364
The Climax Community

Climax vegetation is stable and self-perpetuating
 Clements—monoclimax
 Tansley—advocated polyclimax idea


Historical contingency determines climax composition
Whittaker—developed idea of pattern climax—
a continuum of climax-condition possibilities
based on entire suite of physical factors
Other Concepts of
Ecological Succession
 Communities

Ex:
that do not climax
Prairies, which remain stuck in
early sere because of frequency of
disturbance by fire
 Transient
succession—no climax possible
due to gradually diminishing resources

Exs:
Dung piles
Carcasses
Fig. 18.14 p. 368
Fig. 18.15 p. 369
HANDOUT—Lundsten et al. 2010
Species-Area
Relationships:
Island Biogeography
Arrhenius equation (1921)
S
= cAz
•
•
•
•
S = species richness
A = island area
z = slope
c = constant
 Linear
form:
logS = logc + zlogA
Explaining the Arrhenius
Species-Area Relationship
 Increased
area = increased habitat
heterogeneity (more niches to fill)
 Increased area = increased population
sizes of resident species

Less chance of their stochastic local
extinction
 Increased
area = larger “target” for
dispersing would-be colonizing species
Figs. 21.19 & 21.20 p. 442

c depends on units of
area that are used, but
z does not
 Typically, z ranges
between 0.20 and 0.35
z = 0.32
z = 0.30
The Theory of Island Biogeography



1967 book by Robert A.
MacArthur (Princeton)
and Edward O. Wilson
(Harvard)
Colonization curve:
declines with rising S, as
fewer species are
available to colonize
Local extinction curve:
rises with rising S, as
interspecific interactions
intensify
Fig. 21.21 p. 442
The Dynamic Equilibrium

Point at which the two lines cross
 Balance of new colonists arriving and resident
species going locally extinct

Gains = Losses
Fig. 21.22 p. 443
Krakatau





Indonesian island wiped clean of all life by
enormous volcanic eruption in 1883
1883: 0 bird spp.
1908: 13 bird spp.
1921: 2 bird spp. lost, 16 gained (27 total)
1935: 5 bird spp. lost, 5 gained (27 total)
MacArthur and Wilson’s
Area Effect

Larger areas house larger resident populations
less prone to stochastic extinction
Fig. 21.22 p. 443
MacArthur and Wilson’s
Distance Effect

More isolated habitat islands are more difficult to
reach
Fig. 21.22 p. 443
Area and Distance
Effects Combined

Small, isolated islands:




Rare colonists
High local extinction rate
Low Sequilibrium
Large, nearby islands:



Frequent colonists
Low local extinction rate
High Sequilibrium
Fig. 21.22 p. 443
HANDOUT
Simberloff and Wilson 1969
Nonequilibrium
Island Biogeography
 Dynamic
equilibria are possible only when
colonization can occur
 “Stranded” populations may show
ecosystem decay, with an area effect on
S but no distance effect on S


Islands slowly “bleed” species richness
More rapid loss for smaller islands
 Occurs
naturally, but esp. important in
anthropogenically-isolated habitats
HANDOUT—Brown 1971
HANDOUT—Diamond 1984
HANDOUT—Newmark 1987