Stepping in Elton's footprints: a general scaling model for body masses and trophic levels across ecosystems

• 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. 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 endothermvertebrates) from 35 food-webs (marine, stream, lake and terrestrial). Across all ecosystem and predator types, except for streams (whichappear to have a different size structure in their predator–prey interactions), we find that (1) geometric mean prey mass increases withpredator mass with a power-law exponent greater than unity and (2) predator size increases with trophic level. Consistent with ourtheoretical derivations, we show that the quantitative nature of these relationships implies systematic decreases in predator–prey bodymassratios with the trophic level of the predator. Thus, predators are, on an average, more similar in size to their prey at the top of foodwebsthan that closer to the base. These findings contradict the traditional Eltonian paradigm and have implications for our understandingof body-mass constraints on food-web topology, community dynamics and stability.

Nyckelord

Allometry

body-size ratio

ecological networks

food-webs

predationi

predator-prey interactions

NATURAL SCIENCES

NATURVETENSKAP

Natural sciences

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