Downtown Diet: A global meta-analysis of urbanization on consumption patterns of vertebrate predators

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Siria Gámez and Nyeema C. Harris, Ecology and Evolutionary Biology, Applied Wildlife Ecology (AWE) Lab, Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, Abigail S. Potts, Kirby L. Mills and Aurelia Allen, Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, Allyson Holman, Peggy M. Randon and Olivia Linson, University of Michigan

Background/Question/Methods
Predation is a fundamental ecological process that shapes communities and drives long-term evolutionary dynamics. As the world rapidly urbanizes, it is critical to understand how the built environment and human perturbations alter predation across taxa. We conducted a meta-analysis to quantify the effects of urban environments on three components of trophic ecology in predators: dietary species richness, dietary evenness, and stable isotopic ratios (δ13C and δ15N IR). We then evaluated whether intensity of anthropogenic pressure, using the human footprint index (HFI), explained variation in effect sizes of dietary attributes using a meta-regression. We calculated Hedges’ g effect sizes from 44 studies including 11,986 samples across 40 predatory species in 39 cities globally.
Results/Conclusions
The direction and magnitude of effect sizes varied among predator taxonomic groups with reptile diets exhibiting the most sensitivity to urbanization. Effect sizes revealed that predators in cities had comparable diet richness, evenness, and nitrogen ratios, though carbon isotopic ratios were more highly enriched with δ13C in cities, indicating a shift in diets to include anthropogenic food sources rich in sugar, corn, and wheat. We found that HFI did not explain variation in effect sizes, a result consistent between the 1993 and 2009 editions of this metric. Our study provides the first assessment of how urbanization has perturbed predator-prey interactions for multiple taxa at a global scale, revealing that the functional role of predators is conserved in cities and urbanization does not inherently relax predation, despite diets broadening to include anthropogenic food sources.