Els prats subalpins del Pirineu estan sotmesos a pressions creixents d’abandonament i sobrepastura, amb efectes importants sobre la biodiversitat. Aquest estudi analitza la resposta de les comunitats de plantes i papallones a gradients d’intensitat de pastura i condicions ambientals en deu parcel·les de la Coma de Burg (Pallars Sobirà), utilitzant dades precises de comportament del ramat obtingudes per GPS. S’hi calculen índexs de comunitat basats en valors indicadors ambientals, comparables entre els dos grups taxonòmics. Els resultats mostren que la riquesa de papallones segueix la hipòtesi de la pertorbació intermèdia i que la pastura intensa redueix l’especialització de les comunitats. Els índexs de comunitat de plantes i papallones mostren correspondències coherents, la qual cosa reflecteix la dependència tròfica entre els dos grups. La topografia i la pastura estructuren la biodiversitat de forma independent i complementària, amb implicacions rellevants per a la gestió ramadera adaptativa en el context del canvi climàtic.

In response to increasing human pressures on biodiversity, conservation targets have been set to reduce these pressures and halt biodiversity decline. However, consequences of these objectives on common species are rarely studied. We analyse the effect of a range of drivers related to climate, land use and land-use intensity on 265 common bird and 144 common butterfly species from more than 20,000 sites between 2000 and 2021 across 27 European countries. We use land use and land-use intensity scenarios produced previously using the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) Nature Futures Framework and climate change scenarios to project biodiversity drivers in Europe up to 2050. We translate these driver changes into abundance variations for common bird and butterfly species and for multi-species indicators used to monitor common biodiversity status in Europe. The projected trends relatively improve, while still declining for birds, notably farmland species, under the scenarios meeting conservation objectives, with few effects on butterflies. No scenario shows a stop or a reversal in the average decline in abundance of bird and butterfly species. Our results therefore question the common biodiversity future under current conservation policies and highlight the need for other anticipatory frameworks not implicitly based on a growing need for natural resources.

Abstract The distributions of ecological traits are commonly used to infer the processes structuring ecological communities, as these processes (deterministic or neutral) select and filter species, leading to distinct trait patterns across communities. Trait distributions are frequently characterised by their average, the community‐weighted mean, but increasing evidence exists for non‐Gaussian trait distributions in empirical communities. In such situations, community‐weighted means are insufficient to capture the patterns of community traits and to infer the implied ecological processes. We analysed the empirical distributions of six functional traits of butterflies from a natural community and a filtered community from an urban area across 6 years. All trait distributions were non‐Gaussian, asymmetrical, with relatively long tails (high values of skewness and kurtosis) and multimodal. Results indicate the co‐dominance of some trait values, while others rarely occur, and clear differences between the natural and filtered communities; patterns are only adequately described via statistical descriptors beyond community‐weighted means. Our analyses allowed us to infer that the filtered community is shaped by a mixture of directional and stabilising assembly filters. The consistent results across the 6 years of data provided further evidence of deterministic processes shaping the assembly of our urban community. Overall, we provide evidence of the ubiquity of non‐Gaussian trait distributions across natural and filtered communities, combine multiple statistical descriptors for understanding and comparing such distributions and identify filtering processes structuring these communities.

LepEU, the European Lepidopteran Population Genomics Consortium, was launched in 2023 to coordinate continental-scale collections and generate population-level genomic data for butterflies and moths across Europe. Its whole-genome resequencing strategy takes advantage of the growing availability of reference genomes for Lepidoptera. LepEU supports scalable, standardized sampling and sequencing to quantify genetic diversity and population resilience. These data will allow addressing long-standing questions about geographic patterns of biodiversity in this iconic clade for evolutionary ecology, while also filling critical gaps in biodiversity monitoring and conservation. The consortium's first in-person workshop was held in Montpellier (France) in 2025 and was supported by the COST Action 10kLepGenomes. It gathered 23 researchers from 10 countries, including experts in Lepidoptera ecology, evolution, and population genomics. Building on 2 years of video conferencing, the workshop enabled participants to draw a roadmap for trans-continental standardized sampling, isolate DNA of specimens collected during 2024, outline key research questions for LepEU, and discuss an outreach strategy to engage additional stakeholders. LepEU is coordinating with other international networks and consortia to develop a collaborative platform for tracking European lepidopteran biodiversity and evolution. Looking ahead, LepEU is focused on training and mentoring the next generation of scientists, empowering them to integrate genomic analyses with phenotypic and ecological data to address ecological, evolutionary, and conservation questions.

Grazing influences the spatial and temporal dynamics of vegetation heterogeneity and structure. Whether due to intensification or abandonment, changes in grazing dynamics may cause a variety of habitat responses at different spatio-temporal scales that significantly influence ecological communities. Despite extensive knowledge on the effects of grazing on mountain ecosystems, there is still a limited understanding of how different grazing histories and their legacy (i.e. past long-term effects) interact to shape biodiversity across broad spatial gradients. We aimed to identify the optimal stage of vegetation conditions resulting from particular grazing dynamics and their legacy effects that would maximise butterfly and plant biodiversity across a large geographical range in the Pyrenees. We sought to assess how grazing (either through legacies or immediate effects) influences the richness, abundance, community composition and functional group structure of both plant and butterfly species. We conducted butterfly and plant surveys in 60-x-60m plots in 12 valleys in the Catalan Pyrenees (western Mediterranean) under four different grazing legacy regimes representing different vegetation conditions, ranging from heavily grazed grasslands to densely scrub-encroached areas. We also conducted participatory mapping with local cattle-herders to gain insights into the spatial-temporal dynamics of the grazing legacy regimes. Intermediate grazing stages exhibited significantly higher plant and butterfly richness and abundance, and also harboured species of greater conservation concern. Grazing legacy was the main driver for butterfly and plant diversity, community composition and functionality. Maintaining low to medium grazing intensity is essential for preserving vegetation heterogeneity and enhancing both butterfly and plant richness and abundance.

Aim To examine how butterfly population trends respond to climate change and urbanisation at a continental scale, and whether responses differ between urban and rural environments. Location 869 sites across 12 European countries, spanning six bioclimatic zones. Time Period 1976-2021. Major Taxa Studied Butterflies (Lepidoptera). Methods We analysed long-term monitoring data from > 8400 populations of 145 species representing a wide range of ecological and life-history traits. Population trends were modelled in relation to climate variables (temperature, precipitation and aridity), urbanisation (built-up surface), and their interactions with urban context (urban vs. rural) and species traits (trophic specialisation, body size, reproductive rate and thermal adaptation). Results Climate warming and aridification were consistently linked to population declines in both rural and urban contexts, while precipitation effects varied by location and species. Urbanisation alone did not predict trends, but the urban-rural context strongly modulated species' responses to warming, indicating potential synergies between climate change and urbanisation. The stronger impact of warming in urban populations likely reflects elevated baseline temperatures and reduced habitat suitability and connectivity in urban landscapes, limiting thermal buffering. Species with colder thermal niches and lower reproductive rates were most vulnerable to warming, as warming exceeds the thermal optima of cold-adapted species and lower reproductive rates limit their capacity to buffer climate-driven population declines. Under aridification, which can reduce host-plant availability, trophic specialists declined more in urban areas, whereas generalists unexpectedly declined more in rural sites, suggesting context-dependent constraints under increasing water limitation. Main Conclusions Our findings highlight the complex interplay between climate change, urban context, and species traits in driving population dynamics. Importantly, our results suggest that urbanisation generally amplifies the negative impact of climate change on insect population trends.

Butterfly communities in Mediterranean metropolitan regions are increasingly altered by urbanisation and landscape fragmentation. Using long-term data from the Barcelona Metropolitan Region, this study examines how habitat composition, local landscape dynamics and ecological traits influence butterfly richness, abundance and population trends. Grasslands emerge as the principal habitat predictor of community diversity and specialisation, whereas urbanised areas are associated with reduced butterfly abundance. Population analyses reveal widespread temporal declines, largely driven by local factors; ecological traits played no role, except for a consistent pattern of larger species showing more positive trends. These findings underscore the importance of semi-natural habitats within urban and peri-urban landscapes for maintaining butterfly diversity and highlight the need for conservation strategies that prioritise the ecological quality and connectivity of these habitats.

Understanding the mechanisms behind interaction turnover over long-term periods is essential to predict how ecological networks respond to global change. We used a high-resolution dataset of butterfly-plant interactions spanning 13-29 years in seven Mediterranean communities to assess how climate fluctuations and community shifts shape interaction turnover and its components-species turnover and rewiring. Rewiring contributed the most to interaction turnover, but its relative importance declined over time as species loss reduced the pool of shared partners between years. Consequently, species turnover became increasingly influential, even though communities shifted toward butterfly species with generalist traits that promote rewiring. Nevertheless, rewiring intensified in years with stronger temperature fluctuations, when populations experienced greater shifts in phenology and abundance and were more likely to rewire. In the context of biodiversity loss, species turnover increasingly governs interaction dynamics, while the short-term flexibility provided by rewiring may collapse as communities become impoverished.

Rural abandonment and agricultural intensification are major threats to the conservation of biodiversity in Europe. Butterflies are excellent bioindicators of environmental change and can be used to assess the impact of global change on agroforestry mosaics. We used long‐term spatio‐temporal butterfly data to explore how grazing and mowing practices affect butterfly communities in the semi‐natural grasslands of the northwest Mediterranean Basin. Changes in butterfly richness, abundance and habitat indicators were recorded using standardized transect counts. We focused primarily on the impact of management practices but also considered their interaction with other drivers (climate and habitat configuration). The most intensive levels of grazing did not correspond to the lowest butterfly richness; rather, they were correlated with lower abundances but supported a greater number of open habitat specialists. More intense mowing was also associated with low abundances and communities dominated by common and open‐habitat species. Habitat configuration variables were also influential: open areas favoured greater butterfly richness and abundance, as well as more grassland specialists; greener vegetation, as measured by satellite imagery, led to an increase in butterfly abundance and communities composed of more generalist and forest species. Our study demonstrates the significant impact of grassland management on butterfly communities and offers insights into adaptive rangeland practices. It also indicates that increased levels of mowing and grazing can alter the composition of butterfly communities without necessarily affecting their diversity. This suggests that a dynamic restructuring of butterfly communities may occur in response to the environmental and habitat changes induced by these practices.

The plain tiger Danaus chrysippus is a widely distributed tropical and subtropical butterfly that has expanded its range into the northern Mediterranean in recent decades. This study focuses on its current situation in the Iberian Peninsula, where it was first detected in the early 1980s. Presence records, mainly collated from citizen science portals and Butterfly Monitoring Schemes (BMS), are used to describe the species’ phenology and distribution in the western Mediterranean region, and to assess several hypotheses regarding its summer dispersion. In North Africa and southern Iberia (below 37.5 °N), this species may be present all year, while in the northern Iberian Peninsula (above 37.5 °N) it only occurs seasonally. In both the Iberian Peninsula and the Balearic and Canary Islands, the number of records peaks in autumn. During that season, the plain tiger follows an inland dispersal in the peninsula from the coastline using host plants that grow near rivers and other humid zones. The ecological overlap between the western Mediterranean sub-regions suggests that the ecological characteristics of the southern Iberian Peninsula are more akin to those of North Africa than the north of the Iberian Peninsula and the Balearic Islands. This leads to a partial separation of ecological niches between the northern region and the rest of the area, which helps explain differences in winter survival conditions. The observations of caterpillars and chrysalids during the winter of 2023-2024 in Catalonia provide the first evidence of winter survival at northern latitudes, a phenomenon potentially being driven by climate warming.

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. ### Competing Interest Statement The authors have declared no competing interest.

In response to increasing threats to biodiversity, conservation objectives have been set to halt biodiversity decline by reducing direct anthropogenic drivers. However, the potential effects of these objectives on common species remain rarely studied. We analyse the effect of a range of drivers related to climate, land use and land use intensity, on 265 common bird and 144 common butterfly species from more than 20,000 sites between 2000 and 2021 across 26 European countries. We use land-use and land-use intensity scenarios produced previously using the IPBES Nature Futures Framework, and climate change scenarios in order to project biodiversity drivers in Europe up to 2050. We translate these driver changes into abundance variations for common bird and butterfly species, and for multi-species indicators used to monitor common biodiversity status in Europe. The projected trends relatively improve, while still declining for birds, notably farmland species, under the scenarios meeting conservation objectives, with few effects on butterflies. No scenario shows a stop or a reversal in the average decline in abundance of bird and butterfly species. Our results therefore question the common biodiversity future under current conservation policies and highlight the need for other anticipatory frameworks, not implicitly based on a growing need for natural resources.

Butterflies and moths have often been suggested as suitable indicators for monitoring environmental effects on biodiversity, land use changes and management practices, and many butterfly monitoring schemes are established and run in Europe. In these monitoring programmes, the field counts are only carried out when certain, standard weather conditions considered favourable for butterflies are met. Here, we tested if the prescribed standard weather conditions are suitable across bio-geographic regions, or if the given variance of the weather conditions would still cause effects on monitoring results of butterflies. In addition, we examined how flower density alongside butterfly transects affected the recorded abundance and species number. We operated linear 1-km transect routes in Romania, Spain and Sweden from 2013 to 2015, and recorded butterflies and burnet moths (Papilionoidea, Zygaenidae). The transects were walked back and forth four times per season, and replicated yearly. The following parameters were measured and analysed for their effect on butterfly abundance and species number: country, date and time, temperature, wind speed, sunshine percentage and flower density. In general, weather conditions within the specified range did not cause high variance in recorded butterfly abundance and species richness. In contrast, flower density had a strong impact on butterfly abundance in Sweden and Spain, but less so in Romania. In conclusion, the standard weather conditions imposed and applied in European butterfly monitoring schemes appeared appropriate, for three different bio-geographical and climatic regions across Europe. However, flower density was identified as an important factor affecting butterfly abundance, and is suggested to be routinely recorded as a variable in butterfly monitoring schemes.

Multispecies indicators are an important source of information for quantifying changes in biodiversity. An example is the European Grassland Butterfly Indicator, which gives a trend of 17 species characteristic of European grasslands using data from different European Butterfly Monitoring Schemes. However, adapting this indicator to the regional scale is problematic for several reasons, including changes in habitat preferences in different parts of a species’ range, as well as significant loss of information in highly diverse regions where many local species associate with grasslands. Here we develop a regional indicator that uses data of 143 species present in the Catalan Butterfly Monitoring Scheme, but that weights their contribution according to their degree of association with open habitats. This indicator showed a decline of 54.6

Species show intra-specific variation in responses to climate change linked to adaptation to the local climatic conditions. Likewise, species are expected to be more resilient to climate change at the centre of their bioclimatic niche, but this pattern is not general. We show that species sensitivity to climatic anomalies varies with local adaptation and the position in the bioclimatic niche, using long-term butterfly monitoring data for 34 species. Climatic anomalies negatively affected all populations of locally adapted species. Globally adapted species were positively or negatively affected by climatic anomalies, depending on population location and direction of anomalies. These responses impacted population trends as globally adapted species showed steeper declines at the trailing margin. Surprisingly, locally adapted species showed stable abundances at the trailing margin, but declines at the leading; which could be explained by the with the 'warmer is better' hypothesis where thermodynamics limit insect performance at cooler conditions.

The IPCC predicts that events at the extreme tail of the probability distribution will increase at a higher rate relative to less severe but still abnormal events. Such outlier events are of particular concern due to nonlinear physiological and demographic responses to climatic exposure, meaning that these events are expected to have disproportionate impacts on populations over the next decades (so called low-likelihood, high-impact events -LLHI). Because such events are historically rare, forecasting how biodiversity will respond requires mechanistic models that integrate the fundamental processes driving biological responses to our changing climate. Here we built a matrix population model (MPM) from long-term monitored populations of an insect model species in a Mediterranean area. The model simultaneously integrates the effects of extreme microclimatic heat exposure and drought-induced host-plant scarcity on early life stages, a key methodological step forward because these understudied life stages are usually very susceptible to climatic events. This model for the first time allowed us to forecast the demographic impacts that LLHI events will have on a well-known insect considering their whole life cycle. We found that juveniles were the life stage with the largest relative contribution to population dynamics. In line with field observations, simulated population rates in current climatic regimes were importantly determined by drought impacts, producing a regional mosaic of non-declining and declining populations. The simulations also indicated that in future, climate scenarios not meeting the Paris Agreement, LLHI heat extremes triggered regionally widespread and severe declines in this currently abundant species. Our results suggest that LLHI events could thus emerge as a critical new -but overlooked- driver of the declines in insect populations, risking the crucial ecosystem functions they perform. We suggest that process-based and whole-cycle modelling approaches are a fundamental tool with which to understand the true impacts of climate change.

Intraspecific variation in species relative abundance is shaped by a complex interplay of abiotic and biotic factors, making it both necessary and challenging to assess their combined relative importance in explaining variations across space and time. We used two congeneric butterfly species for which extensive count data and a deep understanding of their natural history is available to test three hypotheses explaining intraspecific variation in their abundance: (H1) seasonal dispersal behaviour driven by climate, (H2) resource availability and (H3) apparent competition mediated via shared parasitoids.Gonepteryx rhamni (Brimstone) and G. cleopatra (Cleopatra).NE Iberian Peninsula, where both species coexist, and a nearby archipelago (Balearic Islands), where only Cleopatra occurs.We analysed spatial abundance variations for both species in the mainland and island–mainland differences in the abundance of Cleopatra. Abiotic and biotic factors, including temperature, host plant and overwintering habitat availability, larval parasitism and density dependence, were tested to explain the observed variations.H1 can explain variation in butterfly abundance between mainland regions since in warmer summers populations increased in cooler areas but decreased in warmer areas. H2 explains the variation within mainland climate regions with a strong positive relationship between resource availability and abundance but is unlikely to explain the island–mainland variation in the abundance of Cleopatra. H3 could neither explain biogeographical variation in abundance because although richer parasitoid communities were found on the mainland, larval mortality rates were similar or lower on the mainland than in the islands.Climate and resource availability jointly account for variation in butterfly abundance across the mainland, but neither these factors nor parasitism can explain island–mainland differences. Both coexisting butterfly species and their larval parasitoids may have undergone evolutionary processes, resulting in spatial segregation that promotes the coexistence of the two butterfly species on the mainland.