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