THE SCALING OF PLANT AND ANIMAL BODY-MASS, LENGTH, AND DIAMETER

The interspecific scaling exponents of body mass M and diameter D with respect to length L were determined to evaluate the predictions of three scaling hypotheses (geometric, stress, and elastic similitude). The relation between M and L was determined for data from a total of 133 aquatic and terrestrial species (66 plant and 67 animal species); the relation between D and L was determined independently for a total of 753 aquatic and terrestrial species (667 plant and 86 animal species). Organisms were crudely classified as to their geometry (spheres, spheroids, cylinders) and shape (defined as the body slenderness factor, L/D) to examine whether geometry and shape evinced size-dependent variations. Regression indicated M = 1.29L(2.95) (r(2) = 0.91, N = 133; alpha(RMA) = 3.09 +/- 0.088). The stress and elastic similitude (which respectively predict alpha(RMA) = 5 and alpha (RMA) = 4) were rejected; geometric similitude was not (alpha(RMA) = 3). For animals and plants, alpha(RMA) = 2.81 +/- 0.061 (r(2) = 0.98), and alpha(RMA) = 2.95 +/- 0.093 (r(2) = 0.94), respectively. For aquatics and terrestrial organisms, alpha(RMA) = 2.82 +/- 0.134 (r(2) = 0.97, N = 36), and alpha(RMA) = 3.08 +/- 0.111 (r(2) = 0.89, N = 97), respectively. These results were interpreted to support the hypothesis of geometric similitude. For the pooled plant and animals data, D = 0.05L(1.00) (r(2) = 0.95; alpha(RMA) = 1.03 +/- 0.009), which was compatible with the hypothesis of geometric similitude. For plants, D = 0.05L(1.06) (r(2) = 0.95; alpha(RMA) = 1.09). For animals, D = 0.29L(0.98) (r(2) = 0.95; alpha(RMA) = 1.O1 +/- 0.025). Also, for aquatics, alpha(RMA) = 0.951 +/- 0.151, whereas for terrestrial plants and animals, alpha(RMA) = 1.03 +/- 0.089. Although the scaling exponent for D differed among individual groupings of animals and plants, the results of regression analyses were interpreted to indicate that, on the average, body diameter scaled isometrically with respect to length as predicted by geometric similitude. For the pooled data set, organic shape varied over 3 orders of magnitude; L varied over 9 orders of magnitude reflecting 22 orders of magnitude of M. In terms of body geometry and the absolute numbers of species in the total data set: spherical shaped species (L = D) < unassigned species < prolate spheroidal species < cylindrical (squat < slender) species. The largest organisms in the data set were slender (L/D > 20) cylindrical plants; the smallest organisms were spherical plants and animals. Although not subject to statistical inference, these data were interpreted to indicate that organic shape and geometry evince size-dependent variations. These variations as well as size-dependent changes in bulk density are hypothesized to account for the scaling exponents of M and D determined for individual plant and animal clades and grades.