Stepping in Eltons footprints: a general scaling model for body massesand trophic levels across ecosystems

Background/ Despite growing awareness of the significance of body-size and predator–prey body-

mass ratios for the stability of ecological networks, our understanding of their distribution within ecosystems is incomplete.

Question/ How is allometry  distributed across ecosystems?

Methods/ Here, we study the relationships between
predator and prey size, body-mass ratios and predator trophic levels using body-mass
estimates of 1313 predators (invertebrates, ectotherm and endotherm vertebrates) from
35 food-webs (marine, stream, lake and terrestrial). Across all ecosystem and predator
types, except for streams (which appear to have a different size structure in their
predator–prey interactions), we find that (1) geometric mean prey mass increases with
predator mass with a power-law exponent greater than unity and (2) predator size
increases with trophic level.

Results/ Consistent with our theoretical derivations, we show that the
quantitative nature of these relationships implies systematic decreases in predator–prey
body-mass ratios with the trophic level of the predator. Thus, predators are, on an
average, more similar in size to their prey at the top of food-webs than that closer to the
base.

Conclusions/ These findings contradict the traditional Eltonian paradigm and have implications
for our understanding of body-mass constraints on food-web topology, community
dynamics and stability.