Rudisser, J. | bioRxiv Science

bioRxiv2025

The interplay of climate change, urbanization, and species traits shapes European butterfly population trends

Species populations naturally fluctuate, yet long-term trend analysis can reveal patterns of success, decline, or stability under global change pressures. While responses to climate change are well-documented, its synergy with another major global driver, urbanization, remains understudied. Here, we analyzed long-term monitoring data from over 8,400 populations of 145 butterfly species across Europe, representing a high diversity of species traits, to assess population trends in response to climate change and urbanization. We examined how population responses vary between urban and rural contexts, providing insights into the influence of site-specific conditions. Climate warming was associated with population declines, which were more pronounced in urban areas. The effect of precipitation varied between environments: increases in precipitation generally benefited populations in rural areas but had detrimental effects in urban ones. Aridity consistently drove population declines across environments, with slightly stronger effects in urban areas. Species with colder climatic niches declined the most in response to warming, increased aridity, and reduced precipitation, while trophic specialists were particularly vulnerable to aridity and precipitation changes in urban environments. Although increasing urbanization did not explain overall population trends, its effects became evident when considering species traits, with certain traits being more vulnerable to urbanization. Specifically, species with narrow climatic niches declined the most in response to urbanization in rural areas, while those and larger body sizes decline the most in urban environments. Our findings highlight the complex interplay between environmental change, landscape context, and species traits in shaping biodiversity outcomes. Importantly, our results suggest that urbanization generally amplifies the impact of climate change on insect population trends.

ecology↗

bioRxiv2025

Urbanisation and Habitat Shape Resource-Driven Dietary Shifts in Wild Birds

Urbanisation affects bird ecology and evolution, with changes in nutritional intake considered a key driver. However, most studies provide only snapshots of urban bird feeding ecology due to methodological limitations in analysing diets across space and time. Here, we address this gap by examining the diets of two common species with differing feeding ecologies: the great tit (Parus major) and blue tit (Cyanistes caeruleus). Diet samples from 370 birds, captured over a year at 147 locations across an urbanised landscape in Innsbruck, Austria, were molecularly analysed. Results revealed species-and season-specific diet patterns influenced by urbanisation: urban great tits exhibited higher diet diversity but reduced arthropod consumption during the breeding season, while urban blue tits compensated for lower moth intake by increasing their consumption of crab spiders and aphids. Prey consumption mirrored prey availability, highlighting resource-driven dietary shifts. Habitat type also played a significant role, with urban green spaces enhancing plant-based food diversity and residential areas increasing anthropogenic food consumption. These findings support the hypothesis that diet drives fitness and phenotypic differences between urban and rural bird populations. They highlight the need to consider both urbanisation levels and habitat characteristics to fully understand its ecological and evolutionary impacts.

ecology↗