American Society of Naturalists

A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.

“Detecting the signature of body mass evolution in the broad-scale architecture of food webs”

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John P. DeLong (Oct 2020)

Resource-based optimization of predator body mass generates macro-scale patterns of predator-prey mass relationships

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A Bold jumping spider (<i>Phidippus audax</i>) consuming a long-jawed orbweaver (<i>Tetragnatha</i> sp). Location: Cedar Point Biological Station, Ogallala, Nebraska.<br />(Credit: John P. DeLong)
A Bold jumping spider (Phidippus audax) consuming a long-jawed orbweaver (Tetragnatha sp). Location: Cedar Point Biological Station, Ogallala, Nebraska.
(Credit: John P. DeLong)

Ecological communities are connected by predator and prey. Those connections are influence by body size, with bigger predators eating bigger prey. Although the positive relationship between predator and prey size seems intuitive, the slope of that relationship varies across taxa, habitats, and temperature. This variation suggests that the structure of ecological communities depends on features of the environment that might also influence the evolution of body size itself, such as temperature and food availability. In this study, the author showed that the slope of the predator-prey body mass relationship could be predicted from a model of body size evolution. Moreover, variation in the body mass relationship could be linked to the time cost of handling prey, indicating that the size of predators is linked to what and how big their prey is in a predictable way. This finding suggests that the broad-scale pattern of who eats whom in a food web emerges from the small-scale processes that drive the evolution of predator body size.


Aody mass-based links between predator and prey are fundamental to the architecture of food webs. These links determine who eats whom across trophic levels and strongly influence the population abundance, flow of energy, and stability properties of natural communities. Body mass links scale up to create predator-prey mass relationships across species, but the origin of these relationships is unclear. Here I show that predator-prey mass relationships are consistent with the idea that body mass evolves to maximize a dependable supply of resource uptake. I used a global databases of ~2,100 predator-prey links and a mechanistic optimization model to correctly predict the slope of the predator-prey mass scaling relationships across species generally and for nine taxonomic subsets. The model also predicted cross-group variation in the heights of the body mass relationships, providing an integrated explanation for mass relationships and their variation across taxa. The results suggest that natural selection on body mass at the local scale is detectable in ecological organization at the macro scale.