van Swaay, C. | 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↗

bioRxiv2022

Large-scale assessment of habitat quality and quantity change on declining European butterflies

The rapid decline of biodiversity as a consequence of increased environmental impact by human activities requires urgent action against the ongoing crisis. At the heart of conservation policy is the debate on quality versus quantity: should the post-2020 Global Biodiversity Framework focus on maximising total protected area, or pursue instead qualitative targets? To improve conservation practices, we need to both understand the current trend of biodiversity and the factors driving the decline. We address this by: (1) projecting current European butterfly population trends for the next 50 and 100 years, (2) comparing the decline in species richness, phylogenetic diversity and habitat specialization among different habitats, and (3) estimating the relationship between recent trends in habitat quality or quantity and the decline of multiple metrics of European butterfly diversity. We do not find any significant relationship between diversity loss and habitat area loss and conclude that neither long-term nor short-term changes in habitat area are primary predictors of large-scale butterfly decline in Europe. Habitat quality emerges as the most crucial factor in our analyses - both the area affected and the severity of habitat quality reduction. Habitat degradation causes vegetation changes in structure and diversity, which affect butterfly survival. We also estimate a higher decline of habitat specialists than generalist species. We conclude that habitat protection cannot focus solely on the maximization of habitat area but urgently needs to restore high quality ecosystems to provide the full range of ecological requirements for biodiversity.

ecology↗