PARENT SESSION
Oral Session #14: Theoretical Ecology. Presiding: C. Klausmeier.
Monday, August 6, 2001. 1:00 PM to 4:30 PM. Hall of Ideas E.
Invariant global allometric scaling relationships for rates of plant biomass production and plant community structure.
ENQUIST, BRIAN1, NIKLAS, KARL2, 1 2
ABSTRACT- Organizing principles are needed to link organismal, community, and ecosystem attributes across spatial and temporal scales. First we compile allometric relationships for plant annualized biomass production (growth) rates, body size (dry weight and length), and photosynthetic biomass (or pigment concentration) for multicellular and unicellular plants. Each of these relationships is described by a single allometric scaling relationship, which spans approximately 20 orders of magnitude in body size. For example, annualized rates of growth G scale as the 3/4-power of body mass M (i.e., G = M 3/4). Second, we extend allometric theory and test its predictions against worldwide data sets for forest communities by quantifying the relationships among tree size frequency distributions, standing biomass, species number, and number of individuals per unit area. As predicted, except for the highest latitudes, the number of individuals scales as the -2 power of basal stem diameter or as the -3/4 power of above ground biomass. Also as predicted, this scaling relationship varies little with species diversity, total standing biomass, latitude, and geographic sampling area. A simulation model in which individuals allocate biomass to leaf, stem, and reproduction and compete for space and light obtains the identical community features. In tandem with allometric theory our results suggest many macroecological features of communities emerge from a few allometric principles operating at the level of the individual. Since these scaling relationships are indifferent to phylogenetic affiliation and habitat, they have far-reaching ecological and evolutionary implications (e.g., community capacity for biomass production is predicted to be largely insensitive to community species composition or geological age).
KEY WORDS: scaling, allometry, biomass, species richness