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Allometric scaling of plant energetics and population density


Scaling relationships that describe variation in population density with body size in ecological communities, such as the thinning law in plant ecology1,2,3, can be explained in terms of how individuals use resources as a function of their size. Data for rates of xylem transport as a function of stem diameter show that rates of resource use in individual plants scale as approximately the 3/4 power of body mass, which is the same as metabolic rates of animals4,5,6,7. Here we use this relationship to develop a mechanistic model for relationships between density and mass in resource-limited plants. It predicts that average plant size should scale as the −4/3 power of maximum population density, in agreement with empirical evidence and comparable relationships in animals5,6,8, but significantly less than the −3/2 power predicted by geometric models1. Our model implies that fundamental constraints on metabolic rate are reflected in the scaling of population density and other ecological and evolutionary phenomena, including the finding that resource allocation among species in ecosystems is independent of body size5,6,8.

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Figure 1: Relationship between the rate of whole-plant xylem transport and basal stem diameter.
Figure 2: Relationship between average plant mass and maximum population density.
Figure 3: Relationship between total plant biomass (roots, shoots and leaves) and maximal population density30.
Figure 4: Relationship between total xylem flux and average size of the dominant plants in diverse ecosystems.


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We thank G. C. Stevens, C. A. F. Enquist, H. S. Horn, T. K. Lowrey, D. Marshall, K. J. Niklas, J. T. Bonner and J. Damuth for their help. B.J.E. was supported by a Fulbright fellowship and funding by NSF; J.H.B. by NSF; and G.B.W. by the US Department of Energy.

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Correspondence to Brian J. Enquist.

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Enquist, B., Brown, J. & West, G. Allometric scaling of plant energetics and population density. Nature 395, 163–165 (1998).

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