Novel and altered diets and nutrition in urban arthropods.

Urban areas are sprawling and densifying worldwide, with the main negative impacts on biodiversity, yet they are also increasingly valued to contribute to conservation efforts. Urban food resources are typically modified and heterogeneous due to human influence, resulting in pronounced gradients that shape the feeding of urban-dwelling species. These conditions influence biodiversity by filtering species through feeding traits and reshaping the diets of urban-adapted species. Here, I synthesise research on arthropod feeding behaviour in urban ecosystems, focusing specifically on diet breadth and nutrient intake. I highlight that food resource structure and availability, and ecological novelty are two critical, variable features characterising urban habitats, in turn shaping feeding behavioural responses of arthropods. I discuss how altered urban resources can enhance or reduce diet breadth, with variable consequences for nutrient intake depending on species and guild, the degree of dietary flexibility, and the ways altered diet and nutrition could indicate stress and suboptimal feeding landscapes. Lastly, I discuss the influence of cognitive capabilities as a critical feature for navigating urban food resource landscapes, and how their ecological novelty might complicate learning mechanisms, such as associative learning, with unknown consequences for arthropod health and fitness. Furthermore, I identify research gaps and outline research directions to improve our understanding of what drives arthropod diet and nutrition in cities, thereby optimising foraging landscapes to support arthropod biodiversity in a changing world.