Abstract
Urbanization is creating a new global biome, in which cities and suburbs around the world often resemble each other more than the local natural areas they replaced. But while urbanization can profoundly affect ecology at local scales, we know little about whether it disrupts large-scale ecological patterns. Here we test whether urbanization disrupts a macroecological pattern central to ecological and evolutionary theory: the increase in seed predation intensity from high to low latitudes. Across 14,000 km of latitude spanning the Americas, we compared predation intensity on two species of standardized experimental seeds in urbanized and natural areas. In natural areas, predation on both seed species increased fivefold from high latitudes to the tropics, one of the strongest latitudinal gradients in species interactions documented so far. Surprisingly, latitudinal gradients in predation were equally strong in urbanized areas despite significant habitat modification. Nevertheless, urbanization did affect seed predation. Compared with natural areas, urbanization reduced overall predation and vertebrate predation, did not affect predation by invertebrates in general, and increased predation by ants. Our results show that macroecological patterns in predation intensity can persist in urbanized environments, even as urbanization alters the relative importance of predators and potentially the evolutionary trajectory of urban populations.
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Data availability
Data used in analyses are publicly available on Borealis, the Canadian Dataverse Repository at https://doi.org/10.5683/SP3/I5DWFQ ref. 69.
Code availability
R code for analyses and figures are also publicly available on Borealis69.
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Acknowledgements
We thank P. Morales, M. MacLaren, V. Javidi, P. Caissy, C. Mulder, P. Hargreaves and F. Baccaro for contributing experimental runs; J. Lane, M. Moffat, J. Best, P. Gomes, B. Ricci and A. Iglesias for help with fieldwork; and É. Charbonneau, É. Meunier, C. Ostiguy, E. and M. Lafond, Gault Nature Reserve for access to sampling sites. The primary funding for this BIG experiment was from an NSERC discovery grant, McGill Liber Ero Conservation Fund grant, and NFRF-R grant to A.L.H. We also acknowledge support from an NSERC graduate scholarship (E.M.); MITACs award (A.R.-C.); NSERC and McGill undergraduate summer research awards (K.L., A.P., V. Javidi, M. Maclaren); and FONCyT (PICT 2019 00969) and CONICET (PIBAA 2022-2023) to M. Chiuffo.
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Authors are listed in order of contribution. A.L.H. designed and coordinated the study, analysed the data and wrote the manuscript. All authors contributed to fieldwork, except O.R.; O.R. and K.L. developed greenness methods and collected greenness data. E.D.-G. made cages and shipped standardized seeds to collaborators in the USA. O.R., J. Burkiewicz, S.H., M.B.B.-B., E.M., M.L.C., T.L.S., M.C.C., I.J.M.TG., S.K.-N., L.P., S.J., K.M., J.F.B., B.F., J.L. and E.S. helped edit the manuscript.
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Extended data
Extended Data Fig. 1 Separate models per predation types vs. one overall model for all predation types.
Top row is the same as Fig. 2, and shows results from 1 model per predation type (column a: total predation by vertebrates and invertebrates, measured using uncaged sunflower seeds; column b: predation by invertebrates only, measured using sunflower seeds caged to exclude vertebrate predators; column c: predation by mostly vertebrates, measured using oat seeds), each with fixed effects Latitude × Urbanization + Elevation. Bottom row shows results from a single overall model including all predation types, with fixed effects Latitude × Urbanization × Predation type + Elevation. Overall conclusions are the same (full statistical results in Extended Data Table 1). Thick lines, shaded polygons and points show means, 95% CI, and partial residuals, respectively. Sample sizes are as in Fig. 2: 156 experimental runs at 36 natural sites and 181 runs at 45 urbanized sites, with 2912, 2394, and 2718 seed depots measuring total, invertebrate, and vertebrate predation, respectively.
Extended Data Fig. 2 Seed predation declined toward higher elevations.
While our study was not designed to test for elevational patterns in seed predation (unlike13, which systematically sampled across elevations within each latitude), we included elevation as a covariate in all analyses of seed predation to account for its effects, and it was always significant (Extended Data Table 3). Elevational trends (mean ± 95% CI) and partial residuals are extracted from one binomial GLMM per predation type (fixed effects: Latitude (absolute) × Urbanization (categorical) + Elevation), plotted for the median absolute latitude (45.0°). While we did not test for interactions between elevation and other fixed effects, we have plotted the elevational trends separately for natural (a) and urbanized (b) sites for illustration. Statistical results in Extended Data Table 3).
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Hargreaves, A.L., Ensing, J., Rahn, O. et al. Latitudinal gradients in seed predation persist in urbanized environments. Nat Ecol Evol 8, 1897–1906 (2024). https://doi.org/10.1038/s41559-024-02504-7
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DOI: https://doi.org/10.1038/s41559-024-02504-7
