Most bumblebee species in Europe are currently not considered endangered. However, given global warming and human land use, this could change dramatically in the future. This is the result of a study that analyzed the past and current distribution of 46 European bumblebee species and made forecasts up to 2080 based on various climate scenarios. Accordingly, if CO2 emissions continue unabated, more than 75 percent of bumblebee species could be threatened with extinction in the future.
Around 90 percent of all wild plants and most crops grown by humans benefit from pollination by animals. In temperate climatic zones in the northern hemisphere, bumblebees are among the most important pollinators alongside honey and wild bees. Although most European species are not yet considered endangered according to the International Union for Conservation of Nature (IUCN), most bumblebee populations have declined significantly over the past few decades and many species have become locally extinct. The reason for this is changes in land use by humans and rising temperatures, which are a problem especially for animals such as bumblebees that are adapted to cold and moderate temperatures.
Past, present and future of bumblebees
“Despite these already serious findings, it has so far been unclear whether the decline has already reached its peak or whether we are just at the beginning of a much more dramatic collapse in bumblebee populations,” writes a team led by Guillaume Ghisbain from the Free University of Brussels in Belgium. “To address this question, we analyzed the past, present and future ecological suitability of the European continent for 46 bumblebee species.”
To do this, the researchers used current and historical data on the distribution and ecological requirements of the various bumblebee species and combined this with data on land use, human population and climate. The historical observation data covers the period from 1901 to 1970, the current ones refer to the period from 2000 to 2014. To forecast future developments up to the year 2080, the team used three different scenarios from the Intergovernmental Panel on Climate Change. The most optimistic scenario assumes an immediate massive reduction in greenhouse gas emissions, the most pessimistic assumes an unabated increase and the middle one simulates a moderated increase.
Ecological niches are shrinking
“Our data shows that bumblebee populations have declined significantly in most parts of Europe since 1900,” the team reports. “We also find that the distribution area will shrink significantly under all future climate and land use scenarios and the species will become extinct.” According to the researchers, the current IUCN assessment, according to which 38 of the 46 species recorded in the study are not endangered, is too optimistic. "For many species currently classified as 'least concern', the regions with suitable ecological niches are shrinking in the face of global change," they explain.
According to the analysis, even in the climate scenario with the lowest emissions, 32 percent of bumblebee species not currently classified as threatened will lose at least 30 percent of their habitat by 2080. Arctic and alpine species such as the alpine bumblebee (Bombus alpinus), which is already endangered, could lose more than 90 percent of their habitat in the same period. From a climatic point of view, parts of Scandinavia could possibly be considered as new refuges. However, it is unclear whether bumblebee populations are able to relocate to these areas and whether human land use is also making these regions uninhabitable for bumblebees.
Bumblebee diversity only in the far north?
While most bumblebee species are experiencing significant population declines, individual species such as the dark bumblebee (Bombus terrestris) and the tree bumblebee (Bombus hypnorum) have benefited from the changes so far. Because they cope better with climate change and human land use than most other species, their populations have increased in recent decades. During the same period, however, several other species disappeared locally in Germany and other European countries.
“If human activities continue unabated, it can be assumed that Europe below 60 degrees north latitude will become largely unsuitable for the continued existence of numerous bumblebee species,” the researchers write. South of Oslo, Stockholm and Helsinki, most bumblebee species would become extinct. “Our results highlight the critical role of global change mitigation measures as effective levers to protect bumblebees from human-induced change in the biosphere,” the team said.
Source: Guillaume Ghisbain (Université Libre de Bruxelles, Brussels, Belgium) et al., Nature, doi: 10.1038/s41586-023-06471-0