No abstract

Although climate-driven phenological shifts have been documented for many taxa across the globe, we still lack knowledge of the consequences they have on populations. Here, we used a comprehensive database comprising 553 populations of 51 species of north-western Mediterranean butterflies to investigate the relationship between phenology and population trends in a 26-year period. Phenological trends and sensitivity to climate, along with various species traits, were used to predict abundance trends. Key ecological traits accounted for a general decline of more than half of the species, most of which, surprisingly, did not change their phenology under a climate warming scenario. However, this was related to the regional cooling in a short temporal window that includes late winter and early spring, during which most species concentrate their development. Finally, we demonstrate that phenological sensitivity—but not phenological trends—predicted population trends, and argue that species that best adjust their phenology to inter-annual climate variability are more likely to maintain a synchronization with trophic resources, thereby mitigating possible negative effects of climate change. Our results reflect the importance of assessing not only species' trends over time but also species’ abilities to respond to a changing climate based on their sensitivity to temperature.

1. One very conspicuous sign that warming is affecting the ecology of butterflies are the phenological advances occurring in many species. Moreover, rising temperatures are having a notable impact – both negative and positive – on population abundances. To date, patterns have generally been analysed at species level without taking into account possible differences between populations, which, when they are noted, are mostly attributed to large‐scale climate differences across a latitudinal gradient. 2. We use a long‐term database (18 years) of butterflies from five sites of the island of Menorca (Balearic Islands, Spain) to investigate how phenology and population dynamics have been affected by climate warming during the past two decades. 3. Both species' phenology and abundance respond differently to warming at a local scale depending on the season. Rising temperatures in spring give rise to greater advancement of the phenology, whereas warming affects population abundance negatively in summer. Additional variability of responses among sites suggests that habitats are involved in the modulation of the aforementioned seasonal effect. 4. We discuss how the effects of temperature could be partially offset in more inland habitats such as forests or deep ravines, especially the latter which represent particularly fresh and humid environments. The positive effect of temperature on ravine populations during the summer suggests that butterflies disperse across habitats as a response to rising temperatures during the season. This dispersal behaviour as a response to warming could be especially important in island ecosystems where the possibilities of modifying altitudinal or latitudinal distributions are often severely limited.

Both the intensification and abandonment of traditional agricultural practices are known to be major threats to biodiversity worldwide, above all in industrialized countries. Although land abandonment in particular has a negative effect on the diversity of both plant and insect communities, few studies have ever analysed these two groups together and none has yet examined the effect on plant-insect interactions using a network approach. In view of the notable decline of pollinator insects reported in past decades, it is essential to understand how the structure of a plant-pollinator network changes during the ecological succession that occurs as traditionally managed habitats are abandoned, and to what extent this network is re-established when habitats are restored. We monitored a butterfly-plant network for 22 years in habitats where land abandonment and restoration have taken place and were able to compare restoration by grazing with restoration combining mowing and grazing. Abandonment leads to significant reductions in the cover of typical grasslands plants and, in turn, rapidly provokes changes in butterfly assemblages and plant interactions. Specifically, it caused a replacement of multivoltine by monovoltine species, increasing network specialization due to the great specificity in the interactions that monovoltine species established with plants. Changes in butterfly communities were also recorded in a nearby unaltered .

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.