Bumblebees are a key taxon contributing to the provision of crop pollination and ecosystem functioning. However, land use and climate change are two of the main factors causing bee decline across the world. In this study, we investigated how the flight period of bumblebee spring queens has shifted over the last century in Sweden, and to what extent such shifts depended on climate change, landscape context, latitude, and the phenology of bumblebee species. We studied ten species of bumblebees and used observations from museum specimens covering 117 years from the southernmost region in Sweden (Scania), combined with citizen-reported observations during the past 20 years across Sweden. We found that the flight period of bumblebees has advanced by 5 days on average during the last 20 years across Sweden. In the agriculture-dominated region of Scania, we found that in the late 2010s bumblebee spring queen activity in simplified landscapes had advanced by on average 14 days, compared to 100 years ago. In addition, in simplified landscapes the flight period of early species was significantly earlier compared to in complex landscapes. Our results provide knowledge on the intraspecific variation of phenological traits, indicating that early species (often common species) exhibit a higher plastic response to the environment, which may facilitate adaptation to both climate and landscape changes, compared to the late species of which many are declining.

1. Dramatic declines of some arthropod populations have recently received a lot of attention. Identified declines have mainly been attributed to changes in agriculture, climate, pathogen prevalence and light pollution, as well as cross-regional effects of, e.g., drifting pesticides. However, the overall picture is complex and debated, and there is a need for systematically collected long-term data, not least from areas relatively unaffected by humans.2. We monitored the abundance of arthropods (mainly insects) in subalpine birch forest in Swedish Lapland over a period of 53 years , in an area comparatively unaffected by human activities. Arthropod abundance was assessed by yearly systematic counts on 24,000 birch shoots, in the second half of June. Animals were categorised into 17 different groups directly upon counting, dependent on taxonomy and life stage (imago, larva).3. Overall, there was no significant change in arthropod numbers. Nor did estimates of the total biomass of arthropods (using group-specific indices of the mass of individuals) show any significant trend. 4. Accordingly, there are no signs that the arthropod abundance or biomass on birch in this subarctic study site has gone through the same declines as have been reported from sites in other habitats. The reason may be that the impact of factors identified worldwide as drivers of arthropod declines so far are small or nonexistent because of the low human population density in this area.

No abstract

No abstract