In migratory insects performing multigenerational migration, such as the painted lady butterfly Vanessa cardui, successive generations face a wide variety of predator communities and may be subject to different predation risks. Here, we analyze the pattern of wing damage of over 2000 butterflies to investigate, for the first time, the risk of predation of adult painted ladies across a latitudinal range of ca 3500 km extending from the northern Mediterranean through the Maghreb to sub-Saharan West Africa. Large number of butterflies showed substantial wing damage attributable to failed attacks, with birds, mantids and lizards being the most likely predators. The risk of attack increased towards the equator, even after controlling for wing wear. In addition, there was a strong effect of butterfly size on predation risk, with larger butterflies facing a higher risk compared to their smaller counterparts, and clear evidence that females suffered more attacks than males. Although size is a major factor, latitude was a stronger predictor of predation risk across the migratory system, as evidenced by greater wing damage in butterflies at lower latitudes, even though their size notably decreased. These results raise an interesting evolutionary conflict, with a tradeoff between size and predation risk, as larger butterflies are likely to be more fecund and efficient in migratory flight but, at the same time, more vulnerable to predation.

Population and community dynamics of butterflies are relatively well known in Europe thanks to citizen science and academic efforts to cover large spatio–temporal scales. However, there are still gaps of knowledge about which life–history traits have a large influence on the dynamics of particular species and the ecological factors that influence those traits. We conducted a capture–recapture demographic study on the comma butterfly Polygonia c–album in a high mountain deciduous forest. We estimated daily survival in breeding adults caught while foraging on thistles and we calculated the probability of dispersal between two close sites. Thistle growth was enhanced by nitrification in cattle grazing in the study area. Local survival was higher for males (0.920, 95 % CI: 0.851–0.959) than for females (0.869, 95 % CI: 0.799–0.917). Short–range dispersal mostly occurred in absence of wind. Light winds and high levels of solar radiation likely enhanced foraging activity. In contrast with findings in most butterfly demographic studies, recapture rates were significantly higher in females than in males, likely due to the latter moving each afternoon to establish territories along sunny forest edges away from the foraging habitat. Further demographic studies are needed to assess the effects of climate stochasticity and habitat transformation caused by changes in extensive cattle grazing on the population dynamics of the comma butterfly.

Mountains harbour a disproportionate amount of biodiversity that is explained by both biotic and abiotic factors. Understanding the ultimate factors that shape these gradients including the interaction between trophic levels is important to highlight management practices that may help maintain biodiversity. Here we report an experiment carried out in a Pyrenean valley where a transhumant cattle herd grazes every year subalpine grasslands in a 700 m altitudinal range (1300–2000 m). In 2018 we measured species richness and abundance of plants and two groups of herbivorous insects (butterflies and grasshoppers) in 20 plots, and then we established 10 exclusion plots to study the effect of grazing during 2019 and 2020. Our results show that there were differences among the relative weight of abiotic and biotic factors that shape biodiversity gradients. Overall, the elevation gradient strongly affected plant, butterfly and grasshopper richness, as well as insect abundances. Plant and butterfly richness’s were correlated via a cascading trophic effect while the slope played a very important role for grasshoppers. Livestock exclusion had a negative effect on plant richness through rapid growth of grass species but there were almost no changes in insect community composition after two years. The intra-annual effects of grazing showed early grazing to be positive for butterflies flying later during the season, as seen for a subset of plots within a narrow altitudinal range. In grazed plots, butterfly richness and abundance increased over the summer when the herd moved to alpine environments and exceeded those of non-grazed plots, indicating that a traditional transhumance management system can help sustain biodiversity in subalpine grasslands as a type of extensive grazing. Implications for insect conservation. Traditional grazing by transhumance systems allows grasslands maintenance in subalpine areas, which helps sustain butterfly and grasshopper populations.

Understanding population responses to environmental conditions is key in the current context of climate change and the extreme climatic events that are threatening biodiversity in an unprecedented way. In this work, we provide a framework for understanding butterfly population responses to weather and extreme climatic seasons by taking into account topographic heterogeneity, species' life-cycles and density-dependent processes. We used a citizen-science database of Mediterranean butterflies that contains long-term population data (28 years) on 78 butterfly species from 146 sites in the Mediterranean mesic and alpine climate regions. Climatic data were obtained from 93 meteorological stations operating during this period near the butterfly sites. We studied how seasonal precipitation and temperature affect population growth while taking into account the effects of density dependence. Our results reveal (i) the beneficial effects of winter and spring precipitation for butterfly populations, which are most evident in the Mediterranean region and in univoltine species, and mainly affect the larval stage; (ii) a general negative effect of summer rain in the previous year, which affects the adult stage; and (iii) a consistent negative effect of mild autumns and winters on population growth. In addition, density dependence played a major role in the population dynamics of most species, except for those with long-term negative population trends. Our analyses also provide compelling evidence that both extreme population levels in previous years and extreme climatic seasons in the current year provoke population crashes and explosions, especially in the Mediterranean mesic region.

Parasitism is a key factor in the population dynamics of many herbivorous insects, although its impact on host populations varies widely, for instance, along latitudinal and altitudinal gradients. Understanding the sources of geographical variation in host-parasitoid interactions is crucial for reliably predicting the future success of the interacting species under a context of global change. Here, we examine larval parasitism in the butterfly Aglais urticae in south-west Europe, where it is a mountain specialist. Larval nests were sampled over 2 years along altitudinal gradients in three Iberian mountain ranges, including the Sierra Nevada, home to its southernmost European population. Additional data on nettle condition and adult butterflies were obtained in the study areas. These data sources were used to investigate whether or not differences in parasitism rates are related to the geographical position and phenology of the host, and to the availability of the host plants. Phenological differences in the host populations between regions were related to the severity of summer drought and the corresponding differences in host plant availability. At the trailing-edge of its distribution, the butterfly's breeding season was restricted to the end of winter and spring, while in its northern Iberian range the season was prolonged until mid-summer. Although parasitism was an important source of mortality in all regions, parasitism rates and parasitoid richness were highest in the north and lowest in the south. Moreover, within a region, there was a notable increase in parasitism rates over time, which probably led to selection against an additional late summer host generation in northern regions. Conversely, the shorter breeding season in Sierra Nevada resulted in a loss of synchrony between the host and one important late season parasitoid, Sturmia bella, which may partly explain the high density of this butterfly species at the trailing-edge of its range. Our results support the key role of host phenology in accounting for differences in parasitism rates between populations. They also provide insights into how climate through host plant availability affects host phenology and, ultimately, the impact of parasitism on host populations.

Los impactos del cambio global sobre la biodiversidad muestran con frecuencia heterogeneidad de respuestas a nivel espacial. Los programas de ciencia ciudadana como el Catalan Butterfly Monitoring Scheme (CBMS) permiten estudiar el estado de las poblaciones de mariposas a largo plazo y en amplias escalas espaciales, y entender así los motores de cambio global que las afectan. En este trabajo se han calculado, utilizando una nueva metodología, las tendencias de un centenar de especies con los datos del CBMS para tres regiones climáticas: alpina, mediterránea húmeda y mediterránea árida. Se han comparado las tendencias de algunas especies comunes entre regiones, así como la relación de dichas tendencias con las características ecológicas de las especies. También se ha estudiado la evolución y cambios de índices ecológicos a nivel de comunidad a partir de transectos de la región alpina con series temporales largas. Los resultados muestran que en las tres regiones el porcentaje de especies en declive supera el de especies en incremento, aunque las comparaciones se han hecho mayormente con especies generalistas y probablemente subestiman el declive que pueden estar experimentando las especies raras. Para las especies comunes, las regresiones han sido más severas en la región mediterránea árida que en la región alpina. En esta última región no se ha encontrado una relación entre las tendencias poblacionales y los índices ecológicos de las especies, pero por el contrario sí se detectan cambios significativos de diferentes índices de la comunidad a nivel local, como resultado principalmente de procesos de abandono del pastoreo y el avance de especies termófilas hacia mayores altitudes.

The Biodiversity and Bioindicators research group (BiBIO), based at the Natural Sciences Museum of Granollers, has coordinated four long-term faunal monitoring programmes based on citizen science over more than two decades in Catalonia (NE Spain). We summarize the historical progress of these programmes, describing their main conservation outputs, the challenges overcome, and future directions. The Catalan Butterfly Monitoring Scheme (CBMS) consists of a network of nearly 200 recording sites where butterfly populations have been monitored through visual censuses along transects for nearly three decades. This programme provides accurate temporal and spatial changes in the abundance of butterflies and relates them to different environmental factors (e.g., habitat and weather conditions). The Bat Monitoring Programme has progressively evolved to include passive acoustic monitoring protocols, as well as bat box-, underground- and river-bat surveys, and community ecological indices have been developed to monitor bat responses at assemblage level to both landscape and climatic changes. The Monitoring of common small mammals in Spain (SEMICE), a common small mammal monitoring programme with almost 80 active live-trapping stations, provides information to estimate population trends and has underlined the relevance of small mammals as both prey (of several predators) and predators (of insect forest pests). The Dormouse Monitoring Programme represents the first monitoring programme in Europe using specific nest boxes for the edible dormouse, providing information about biological and demographic data of the species at the southern limit of its distribution range. The combination and complementarity of these monitoring programmes provide crucial data to land managers to improve the understanding of conservation needs and develop efficient protection laws.

The impact of global change on biodiversity often has heterogeneous responses at a spatial scale. Citizen science programs such as the Catalan Butterfly Monitoring Scheme make it possible to study butterfly responses in the long term and over wide spatial scales, which thus helps understand the drivers of global change that are affecting them. In this work a novel methodology and the CBMS data have been used to calculate trends for a hundred species from three climatic regions: Alpine, humid Mediterranean and arid Mediterranean. A comparison between regions of the trends of a number of common species was made, as well as the relationship between these trends and species' ecological characteristics. Changes in the communities at a number of long-term monitored sites were also studied in the Alpine region using several community indices. The results show that in the three regions the percentage of species in decline exceeds that of the species that are increasing. Nevertheless, these comparisons were made using a mainly generalist fraction of the fauna and probably underestimate the declines that certain rare species are suffering. In common species, declines were more severe in the arid Mediterranean region than in the Alpine region. In this latter region there was no relationship between population trends and the ecological indices of the species. Conversely, significant changes were detected in certain community indices at local level, mainly due to the abandonment of grazing and the movement of thermophilic species towards higher altitudes.

In many migratory insects, migration occurs during the prereproductive phase of the life cycle. This trait probably arises from a trade-off between migration and reproduction and in females has been termed the 'oogenesis-flight syndrome'. However, the generality of this syndrome has been questioned, especially for monomorphic insects. We studied the relationship between migration and reproduction in the highly cosmopolitan painted lady butterfly, Vanessa cardui, which in the Palaearctic undertakes the longest known multigenerational migration circuit of any insect. We tested for the oogenesis-flight syndrome in both spring and autumn migrants in two regions linked by migration, North Africa and northern Spain. Field observations were combined with laboratory experiments to determine the life span and the age at first mating to unravel the reproductive strategy observed in wild-caught individuals. Females and males wait on average around 5-6 days before mating, and field data revealed that mating frequencies increased rapidly once females reached a medium wing wear category. There were seasonal differences in mating frequencies in the study regions depending on whether the region acted as a source or as a destination for migrants, and in the latter case there were almost twice as many mated females. Moreover, a great majority of females collected during migratory flights were unmated, the remaining females having mated only very recently. Our results thus strongly indicate that the painted lady fulfils the oogenesis-flight syndrome, as migration is concentrated in its relatively short prereproductive period. Field data also showed a high positive correlation between mating frequency and host plant abundance, which suggests that mated females are able to locate potential breeding areas. This, together with the high fecundity estimated in laboratory trials, makes the painted lady a highly successful migratory insect. (c) 2020 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

EnglishAfter years without significant damage, in 2018-2020 an outbreak of the gypsy moth, Lymantria dispar (Linnaeus, 1758), defoliated large areas of cork oaks and holm oaks in the Montnegre mountains. The onset of this outbreak could be related to the collapse of mice and shrew populations that regulate the moth populations when they are at low densities. A literature search reveals the existence of a very extensive complex of natural enemies that prey on the gypsy moth, some of which provoke density-dependent mortality that predictably leads to a return to normal populations levels within a period of 1-4 years. Several species of parasitoids and the beetle Calosoma sycophanta (Linnaeus, 1758) have been detected in the study area. In addition, the monitoring of egg-clusters in 10 defoliated and 10 unaffected localities in 2019 showed that around 50 % of the egg masses suffered predation at the outbreak sites. In May 2020, approximately 2,500 ha of forest were treated with Bacillus thuringiensis (Berliner, 1915) var. kurstaki to combat the pest. To assess the effectiveness of this measure, we designed a systematic survey in 15 areas, whose results show that the use of this insecticide did not reduce defoliation when comparisons were made with antreated areas. Moreover, we noted that defoliated trees, especially cork oaks, recovered well and a month after the peak of the infestation showed defoliations of only 15 %. In Catalonia, we thus consider that there is currently no argument in favour of using this method to combat sporadic outbreaks of L. dispar catalaDespres d’anys sense afectacions severes, l’eruga peluda del suro, Lymantria dispar (Linnaeus, 1758), ha defoliat grans superficies de suredes i alzinars al Montnegre entre 2018-2020. L’inici d’aquest episodi eruptiu podria estar relacionat amb un col·lapse de les poblacions de ratolins i usaranyes, que regulen les poblacions de la papallona quan aquestes es troben en baixes densitats. Un recull bibliografic posa de manifest l’existencia d’un complex molt extens d’enemics naturals al voltant d’aquest lepidopter, alguns dels quals actuen de forma dependent de la densitat i, previsiblement, retornaran les poblacions a nivells habituals en un periode d’1-4 anys. A la zona afectada s’han detectat diverses especies de parasitoides i l’escarabat Calosoma sycophanta (Linnaeus, 1758). A mes, un seguiment en 10 localitats defoliades i en 10 localitats poc afectades el 2019 demostra que, en les zones eruptives, al voltant d’un 50 % de les postes de L. dispar van patir depredacio, possiblement per part d’ocells. El maig de 2020, aproximadament 2500 ha de bosc es van tractar amb Bacillus thuringiensis (Berliner, 1915) var. kurstaki per combatre la plaga. Per avaluar l’efectivitat d’aquesta mesura es va dissenyar un seguiment que demostra que l’us de l’insecticida no ha minimitzat els nivells de defoliacio en relacio a les zones no tractades. Tambe s’ha constatat una recuperacio molt important dels arbres, especialment dels suros, que un mes despres del pic de l’afectacio presentaven defoliacions de nomes un 15 %. A Catalunya, considerem que actualment no hi ha cap argument en favor d’utilitzar aquest metode per combatre els episodis eruptius esporadics de L. dispar

Land abandonment and loss of grazing have been amongst the primary drivers of landscape change in the Mediterranean basin in the recent decades. As a consequence, forest cover has greatly expanded in detrimental of semi-natural grasslands, areas of cultivation and pasture mosaics. Although predictably important, the impact that this phenomenon has on biodiversity has remained largely unexplored, partly because of lack of appropriate data. Here, we make use of an extensive citizen science program, the Catalan Butterfly Monitoring Scheme, to quantify the response of butterfly assemblages to vegetation encroachment in NE Spain. We first adapted an index to describe the preference of 147 butterfly species for open or closed habitats and found a strong association of most species for open habitats. We developed a community index to record changes in 54 long-term monitored sites (10 years or more), where plant communities were also periodically monitored. Butterfly assemblages have undergone changes toward species preferring closed habitats in 72% of the studied sites, in parallel to a process of vegetation encroachment in the region. Community changes were linked to population trends, and could be locally predicted by the interaction of the preference of butterfly species for open or closed habitats and the magnitude of vegetation encroachment at each site. These changes were accompanied by frequent extinction events (4.53% of the studied populations), that were highly biased toward species preferring open habitats. Our study confirms and quantifies the threat that vegetation encroachment imposes on biodiversity in this highly diverse region.

The climatic preferences of the species determine to a large extent their response to climate change. Temperature preferences have been shown to play a key role in driving trends in animal populations. However, the relative importance of temperature and precipitation preferences is still poorly understood, particularly in systems where ecological processes are strongly constrained by the amount and timing of rainfall. In this study, we estimated the role played by temperature and precipitation preferences in determining population trends for birds and butterflies in a Mediterranean area. Trends were derived from long-term biodiversity monitoring data and temperature and precipitation preferences were estimated from species distribution data at three different geographical scales. We show that population trends were first and foremost related to precipitation preferences both in birds and in butterflies. Temperature preferences had a weaker effect on population trends, and were significant only in birds. The effect of precipitation on population trends operated in opposite directions in the two groups of species: butterfly species from arid environments and bird species from humid habitats are decreasing most. Our results indicate that, although commonly neglected, water availability is likely an important driver of animal population change in the Mediterranean region, with highly contrasting impacts among taxonomical groups.

1. The painted lady Vanessa cardui is a long‐range migratory butterfly that performs an annual multi‐generational round‐trip between Europe and Africa. Each autumn it returns to northwest (NW) Africa, presumably to track changes in resources that follow a predictable climate‐related spatio‐temporal pattern.2. Data on the abundance of adult and immature stages in the Maghreb in 2014–2016 are used to test several hypotheses regarding the autumn migration of this species.3. A strong seasonal migratory strategy was confirmed by the all but total absence of the species in NW Africa at the end of summer and the arrival of huge numbers migrants in October and November. Migration was timed to coincide with an increase in host plant availability but not with any increase in nectar sources.4. Flower abundance was the main predictor of adult abundance in autumn, with Ditrichia viscosa, Verbesina encelioides, and Medicago sativa being key resources that attracted enormous numbers of butterflies to oases, ruderal habitats, and oueds. The distribution of immature stages was strongly predicted by host plant abundance (with traditional agriculture representing the most important breeding habitat) and latitude (most breeding occurred in the south of the region). Also, both adults and immature stages were more common inland than in coastal areas.5. Changes in age structure of the adult population were also noted. The number of fresh adults slowly increased, indicating that butterflies did not return in a single wave and that the first offspring of the first returners were already emerging when some butterflies were still arriving.

Global change analyses usually consider biodiversity as a global asset that needs to be preserved. Biodiversity is frequently analysed mainly as a response variable affected by diverse environmental drivers. However, recent studies highlight that gradients of biodiversity are associated with gradual changes in the distribution of key dominant functional groups characterized by distinctive traits and stoichiometry, which in turn often define the rates of ecosystem processes and nutrient cycling. Moreover, pervasive links have been reported between biodiversity, food web structure, ecosystem function and species stoichiometry. Here we review current global stoichiometric gradients and how future distributional shifts in key functional groups may in turn influence basic ecosystem functions (production, nutrient cycling, decomposition) and therefore could exert a feedback effect on stoichiometric gradients. The C–N–P stoichiometry of most primary producers (phytoplankton, algae, plants) has been linked to functional trait continua (i.e. to major axes of phenotypic variation observed in inter-specific analyses of multiple traits). In contrast, the C–N–P stoichiometry of higher-level consumers remains less precisely quantified in many taxonomic groups. We show that significant links are observed between trait continua across trophic levels. In spite of recent advances, the future reciprocal feedbacks between key functional groups, biodiversity and ecosystem functions remain largely uncertain. The reported evidence, however, highlights the key role of stoichiometric traits and suggests the need of a progressive shift towards an ecosystemic and stoichiometric perspective in global biodiversity analyses.