Abstract
Predation is a fundamental ecological process that shapes communities and drives evolutionary dynamics. As the world rapidly urbanizes, it is critical to understand how human perturbations alter predation and meat consumption 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 (IRs) (δ13C and δ15N IR). We evaluated whether the 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. The direction and magnitude of effect sizes varied among predator taxa with reptilian diets exhibiting the most sensitivity to urbanization. Effect sizes revealed that predators in cities had comparable diet richness, evenness and nitrogen ratios, though carbon IRs were more enriched in cities. We found that neither the 1993 nor 2009 HFI editions explained effect size variation. Our study provides, to our knowledge, the first assessment of how urbanization has perturbed predator–prey interactions for multiple taxa at a global scale. We conclude 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 such as sugar, wheat and corn.
Highlights
Predation is a process that underpins ecological and evolutionary dynamics at various scales, from the individual to the ecosystem
When effect sizes were pooled for all predator taxa, ΔHFI2009 did not significantly affect consumption metrics (DSR: β = 0.029, 95% CI = −0.02 to 0.08; DEV: β = −0.002, 95% CI = −0.19 to 0.15; δ13C: β = −0.003, 95% CI = −0.31 to 0.29; δ15N: β = −0.002, 95% CI = −2.1 to 2.18)
Our global meta-analysis revealed that predator trophic ecology changed significantly in carbon consumption but was conserved for other diet metrics
Summary
Predation is a process that underpins ecological and evolutionary dynamics at various scales, from the individual to the ecosystem. We expected trophic responses to urbanization to differ significantly among predator taxa, owing to implicit differences in diet plasticity, behaviour and natural history as well as biased representation of taxa in urban ecology literature [55,56] Such variation in sensitivity to perturbations in urban ecosystems may drive heterogeneity in the direction and significance of effect sizes among wildlife taxa [57,58]; and (iii) how do urban effects on predation relate to the HFI? Without a unified definition of ‘urban’ or use of standardized response variables in the urban ecology literature, we defined the selection criteria for inclusion in the analysis in that prospective studies needed: (i) direct measures of diet composition through observation, scat, pellets or necropsy, and (ii) summary data of diet metrics for both urban and rural categories to calculate effect sizes. We found little evidence that the degree of anthropogenic change on the landscape significantly influenced the magnitude of effect sizes of urbanization on predation
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