Ella Martin

Urbanization is causing unprecedented ecological and evolutionary change worldwide. However, empirical evidence of local adaptation to urban environments is limited. Here we conduct a reciprocal transplant experiment using white clover (Trifolium repens) originating from urban and rural populations and distributed equally into five urban common gardens and five rural common gardens. Half of the plants in each garden produced the antiherbivore chemical defence hydrogen cyanide (HCN), and the other half lacked the defence, as this trait is known to exhibit genetic clines along urbanization gradients. Based on measurements of multiple vegetative and sexual fitness traits as well as ecological interactions with herbivores, pollinators and mutualistic root bacteria, we detect divergent selection on HCN between urban and rural environments, where HCN improved fitness in rural environments and reduced fitness in urban environments. Urban and rural white clover populations show genetic divergence that drove a tradeoff in life history strategies: urban plants invested more in vegetative growth, whereas rural plants produced more flowers and seeds in both urban and rural gardens. Finally, we demonstrate eco-evolutionary feedbacks, with increased herbivory at rural sites, and increased pollinator visitation to acyanogenic plants at urban sites. This study contributes to understanding how urbanization affects evolution and feeds back to influence broader ecosystem processes.

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.

As urbanization expands, it is becoming increasingly important to understand how anthropogenic activity is affecting ecological and evolutionary processes. Few studies have examined how human social patterns within cities can modify eco‐evolutionary dynamics. We tested how socioeconomic variation corresponds with changes in trophic interactions and natural selection on prey phenotypes using the classic interaction between goldenrod gall flies (Eurosta solidaginis) and their natural enemies: birds, beetles, and parasitoid wasps. We sampled galls from 84 sites across neighbourhoods with varying socioeconomic levels, and quantified the frequency of predation/parasitism on flies and natural selection by each enemy. We found that bird predation was higher in the highest income neighbourhoods, increasing the strength of selection for smaller galls. Wasp and beetle attack, but not their strength of selection, increased in lower income neighbourhoods. We show that socioeconomic variation in cities can have strong unintended consequences for the ecology and evolution of trophic interactions.

Urbanization can profoundly disrupt local ecology. But while urban areas now stretch across latitudes, little is known about urbanization’s 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 Summary Across 56,000 seeds and 112° of latitude, latitudinal gradients in seed predation are equally strong in natural vs. urban areas