Rodriguez-Campbell, A. | Search bioRxiv

bioRxiv2023

Latitudinal gradients in predation persist in urban environments

Urbanization can profoundly disrupt local ecology. But while urban areas now stretch across latitudes, little is known about urbanizations effects on macroecological patterns. We used standardized experiments to test whether urbanization disrupts latitudinal gradients in seed predation, a macroecological pattern that shapes community assembly and diversity. Using >56,000 seeds, we compared predation in urbanized and natural areas across 14,000 km of latitude, spanning the Americas. Predation increased 5-fold from high latitudes to the tropics, and latitudinal gradients in predation persisted in urban areas despite significant habitat modification. Urbanization reduced predation by vertebrates, but not invertebrates, and seemed to increase ant predation specifically. Our results show that macroecological patterns in predation intensity can persist in urbanized environments, even as urbanization alters the relative importance of predators. One-Sentence SummaryAcross 56,000 seeds and 112{degrees} of latitude, latitudinal gradients in seed predation are equally strong in natural vs. urban areas

ecology↗

bioRxiv2023

Clay larvae do not accurately measure biogeographic patterns in predation

AimSpatial variation in predation can shape geographic patterns in ecology and evolution, but testing how predation varies across ecosystems is challenging as differing species compositions and defensive adaptations can mask underlying patterns. Recently, biogeography has borrowed a tool from ecology -clay prey models. But clay models have not been adequately tested for geographic comparisons, and a well-known problem -that clay prey only appeal to a subset of potential predators- could lead to inaccurate detection of geographic patterns whenever the relative importance of predator guilds varies among sites. Here, we test whether clay larvae accurately capture geographic differences in predation on real larvae. Location90{degrees} of latitude and >2000 m elevation across the Americas Taxonvertebrate and invertebrate predation on superworms (Zophobas larve) MethodsAcross six sites that vary dramatically in latitude, elevation, and biome, we quantified predation on live, dead, and clay larvae. We physically excluded vertebrate predators from some larvae to distinguish total predation and invertebrate-only predation. ResultsPredation on live superworms almost doubled from our high-elevation high-latitude site to out low-elevation tropical site. Geographic patterns were highly consistent among live and dead larvae, but clay larvae missed extremely high predation at some sites and therefore mismeasured true geographic patterns. Clay larvae did a particularly bad job at capturing geographic patterns in predation by invertebrates. Main conclusionsClay larvae are inappropriate for large-scale tests of predation, and should be abandoned for biogeographic studies. Biogeographic experiments should instead employ realistic baits, and clay prey should be reserved for comparisons within, rather than across, predator communities.

ecology↗