BIOLOGY 301
A. Succession terminology
1. Succession: changes in a community at a site following
either habitat disturbance or colonization of a new
substrate
2. Primary succession: establishment and subsequent changes
in a community from newly formed habitats without
plants (sand dunes, lava flows, newly exposed rock,..).
Involves much modification of the environment by early
colonists = pioneer species (such as lichens and
mosses, beach grasses) which in terrestrial
environments stabilize and enrich or even generate soil
3. Secondary succession: changes at a site that previously
had a community and then suffered a major perturbation
which reset the stage of the community to an earlier
point in the succession process but did not reset it to
the primary succession stage
4. Climax: the ultimate stable association of plants and
animals. It is self-perpetuating i.e. plants and
animals can succeed themselves. The climax for a site
is dependent on the topography, climate, disturbance,
etc. characteristic of that site.
5. Sere: the organisms in a community at a given point in
the successional sequence. The final sere is the
climax.
B. Primary succession
1. Sand dunes on Lake Michigan (Indiana sand dunes of
Clements)--can walk through the seral stages on a line
perpendicular to the lake shore, going from young to
older and older seral stages.
a. Sand dunes on shore
b. Perennial grasses: stabilize and add organics
c. Annuals: further enrich soil and stabilize
d. Shrubs
e. Pines
f. Forest: first black oak and then beech and maple
2. Atlantic coastal sand dune pattern is similar
a. Sea oats and beach grass: stabilize and add organics
b. Bayberry and beach plum and other shrubs: stabilize
and catch sediments
c. Pines
d. Coastal forest
3. Receding glaciers in Alaska (thin clay deposits)
a. Mat-forming mosses and sedges
b. Prostrate willows
c. Shrubby willows
d. Alder thicket
e. Spruce-hemlock forest C. Secondary succession--reset of established community to an
earlier stage by physical or biotic process
1. Clearcut forest
a. Annuals
1. Crabgrass to horseweed to ragweed
2. Aster to broomsedge--both of these are biennial
b. Herbaceous perennials and shrubs
c. Pines
d. Hardwoods such as oak and maple
2. Size of disturbance determines the amount of the reset
and from where the colonists come
a. Forest
1. Decrease number of limbs on trees--neighbors
fill in
2. Cut/blowdown tree in forest--saplings already
present fill in
3. Cut/blowdown number of trees in forest so a
much larger gap--colonize by seeds and
usually the plants of the mature forest
cannot live in such large open gaps due to
amount of sunlight
a. Colonists dependent on availability at the
time of disturbance (potential
importance of seed bank), state of the
habitat and the ability of the recruit
to live there
b. Mussel bed in the rocky intertidal
1. Remove a mussel--surrounding individuals close
gap
2. Remove number of contiguous individuals--gap
will often grow due to wave forces and such
large gaps are colonized by water borne
propagules
D. Climax for a given locale
1. Is a function of climate and topography and presence of
disturbance factors such as fire, landslides, and
predators
2. Fire dependent
a. Shrubby vegetation of Californian foothills is the
chaparrel
1. without fire the vegetation is replaced by oaks
b. Prairie
1. Grasses root sprout following a fire while
hardwood seedlings are killed
2. Grasses produce lots of litter, increase
probability of fire
3. Biotic disturbance dependent
a. Predator
1. Rocky intertidal with mussels and Pisaster
b. Burrowing organisms
1. Prairie dog mounds in grasslands
2. Badgers in grasslands
3. Infaunal holothurians
E. Mechanisms of succession
1. Facilitation
a. Each seral stage changes the characteristics of the
environment making it unsuitable for itself
(especially for its seedlings) and suitable for
the members of the next seral stage
b. Pine seedlings do not survive in shade but maple
seedlings do
c. Hydroids increase mussel recruitment
2. Inhibition
a. Species can prevent colonization of another
b. Course of succession is dependent on which species
arrive first and the next seral stage will only
occur following the death of those individuals and
the successful colonization of the next' set of
species
c. Black oaks change the soil pH to 4.0 which inhibits
the establishment of the beech-maple climax which
prefers pH 7.0
3. Tolerance
a. Whatever can live there will and the best competitor
for resources will win
b. No large amount of inhibition or facilitation
c. Progress of succession dependent upon the lifespans
of the individuals and the competitive abilities
of the colonists
F. Climax characteristics
1. Propagules can survive under adults i.e. individuals of
same species can succeed the adults
2. Characteristics of plants:
Early stage Late stage
Number of seeds ## few
seed size small large
dispersal wind, stuck gravity, eaten
to animals
seed viability long short
(seed bank)
root:shoot ratio low high
growth rate rapid slow
mature size small large
shade tolerance low high
3. As go up in seral stage:
a. Increasing amount of nutrients in organic materials
b. Increasing amount in supportive tissue (less edible)
c. Soil loss of nutrient reduced due to roots
d. Canopy buffers heat and desiccation stress i.e.
greater impact of organisms on local physical
conditions
4. Study by
a. Count numbers per area and size and age per
individual
b. Determine replacement