smaller than their animal prey are called parasite chains. If the mass of the
consumer (predator or parasite) is related to the mass of the animal resource
(prey or host) by a power law with exponent less than 1, then, in predator chains,
there is an upper limit to the mass of the largest predator and prey, and in
parasite chains, there is a lower limit to the mass of the smallest host and
parasite. These limits are independent of the number of trophic links in the
chain and independent of the mass of the basal animal species. In a predator
chain that obeys this allometric relation of predator and prey masses, the ratio
of predator mass to prey mass decreases as the trophic level and mass of the prey
increase. In a parasite chain that obeys this allometric relation of predator and
prey masses, the ratio of parasite mass to host mass increases as the trophic level
of the host increases and the mass of the host decreases. In the data on predator
chains here, predator masses generally exceed prey masses. The regression of
the logarithm of predator mass on the logarithm of prey mass has slopebless
than 1 in all cases. While it is possible to calculate maximal predator sizes from
these regressions, estimates of maximal predator size are highly sensitive to
uncertainty in the parameters of the regression lines. For three collections of
data from coastal communities, 0<b<1/2, while for three collections of data
from terrestrial communities, 1/2<b<1. A model of the joint distribution of
consumer and resource body masses predicts a slope of 1/2 for both predator and
parasite chains, and specifies conditions under which the slope should deviate
up or down from 1/2. The theory developed here pertains to isolated chains, but
all the data are drawn from webs with interconnecting chains. An ideal test of
the theory would describe the full frequency distribution of body sizes of each
species in a more or less isolated chain, if such can be found in nature. It would
also be useful to extend the theory from isolated chains to more complex food
webs and to analyze the consequences in the variability of body sizes of both
resources and consumers.Acknowledgements
I am grateful for helpful, critical comments on previous drafts from John Tyler
Bonner, Benni Hansen, Mark Huxham, Tomas Jonsson, Mark Laska, Robert H.
Peters, Dave Raffaelli, Thomas W. Schoener, Alain Ve ́zina and two reviewers; the
support of US National Science Foundation grants BSR92-07293, DEB 9981552
and DMS-0443803; the assistance of Priscilla K. Rogerson; and the hospitality of
Mr and Mrs William T. Golden during this work.References
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694–702.BODY SIZES IN FOOD CHAINS 323