Latitudinal gradients in seed predation persist in urbanized environments

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. Seed predation increases from the Arctic to the tropics, but it is unknown whether urbanization disrupts this latitudinal pattern. An experimental study conducted across the Americas shows that the latitudinal gradient in predation holds in urban areas, even though total seed predation is reduced.