Lecture graphics

Modern discussions of the community concept include the following elements:

1. Vegetation and climate are inseparable

   Greek philosopher Hippocrates (400-370 B.C.) recognized effect of environment on plants

   Biggest advocate was Clements, but even Gleason agreed with this concept

   Clements defined climax as a product of, and controlled by, climate (organismic view)

   Shreve, then Gleason and Raminsky--species vary gradually along environmental gradients

   We can extend the concept of inseparability to environment (vs. merely climate)

   Extrinsic factors--environment per se

   Intrinsic factors--environment as influenced by plants

   
   
   
   
   

   Jack Major (1951, J. Ecol. 32:392-412) modified Hans Jenny's equations of state for soil-forming factors to formalize the relationship between vegetation and environment: veg = f(organisms, climate, soil, time) (i.e., veg = f (environment)

2. Species in community interact--at least some of the species, some of the time (degree of interaction is focus of considerable debate)

   Demonstrating interaction does not infer that the interaction shapes community structure

   However, to the extent that interactions dictate resource allocation, these interactions can contribute to the organization of plants into communities

   Westhoff (1951, Synthese 8:194-206) summarized these two concepts (with a Clementsian slant):

   The notion of the plant community as a collection of individuals that are more or less regularly grouped in space is not only a statement of fact derived from experience, but it is also an hypothesis: that plants in such groupings are interrelated and that their combination is not merely the result of a selection by an extrinsic environment.

3. Communities are delimitable in space and time; thus, communities have boundaries

   Two interpretations of community

   ~ stand (concrete): acc. to proponents of the individualistic view, no two are identical; therefore, community as an organism does not exist

   ~ association (abstract): class concept, of which members are stands (examples) of the concept

   
   
   
   

4. Communities are characterized by some degree of compositional and structural homogeneity

   Disturbance and/or development --> inability to recognize the community

   Usu. based only on spp. composition and abundance, but Drake (1990 TREE 5:159-164) indicates that energy flow should be the basis. Drake acknowledges this will be difficult to measure, but writes: "nature proceeds without regard to human logisitical and analytical sophistication."