Bumblebees are not just welcome visitors to our gardens. As efficient pollinators, they also play an important role in agriculture. But in addition to habitat loss, climate change is increasingly endangering these industrious insects. As a study now shows, the bumblebees are disappearing drastically in many regions of Europe and North America. This phenomenon appears to be related to the more frequent occurrence of weather extremes such as heat waves and droughts, the researchers report.
Without insects, there would be significantly fewer fruits and vegetables. Because many crop plants rely on pollination by bumblebees and the like. The development that agricultural ecologists and biologists have been observing for some time is all the more worrying: the drastic decline in many important pollinator insects. The main reason for the disappearance of the hard-working helpers is intensive agriculture and changing land use. Because they lead to the insects finding less retreat and food. In addition, the pesticides, which are widely used in fields and fields, are a problem for them. But there is another factor that could contribute to insect death. Experts suspect that climate change also plays a role. However, researchers are only just beginning to understand how exactly certain species react to changing climatic conditions.
Climate change factor
Peter Soroye from the University of Ottawa and his colleagues have now investigated what influence global warming has on bumblebees in particular. For their study, they evaluated a large data set on the distribution of 66 species of bumblebee in Europe and North America. They compared the two periods 1901 to 1974 and 2000 to 2014 and also evaluated local weather data from these years. The terrifying result: the bumblebees seem to disappear in many places. For example, the average likelihood that a region is populated by bumblebees has declined by 46 percent in North America and 17 percent in Europe. The bumblebee populations in southern climes such as Spain or Mexico are particularly affected by this decline.
The crucial point: the disappearance of the insects seems to be directly related to the more frequent occurrence of weather extremes such as heat waves and droughts. Such extremes affected the spread of bumblebees more than the permanent rise in average temperature, the team reports. The results also showed that the bumblebees sometimes move to more northern, cooler regions. However, they colonize far fewer of these alternative habitats than they have lost in the south. “We have known for a long time that climate change means an increased risk of extinction for many animals,” says Soroye. “For bumblebees, this is apparently due to hotter and more frequent extreme temperatures.”
Questionable shrinkage of pollinators
According to the researcher, the observed rate of bumblebee shrinkage corresponds to that of a mass extinction. “If the decline continues at this rate, many of these species could disappear forever within a few decades,” he warns. The consequences would be serious: “Since bumblebees have a social lifestyle and are active even at low temperatures, they are considered extremely efficient pollinators and are also used as pollinators in agriculture for fruit and vegetables and in garden centers. Among the wild bees, they are the species group with the highest pollination efficiency, ”comments Axel Hochkirch from the University of Trier, who was not involved in the study.
The biologist explains that the bumblebee shrinkage on our continent is less strong than in North America due to the additional pressure caused by the intensification of the agricultural economy: “Intensive agriculture in very large regions of the USA – for example in the so-called ‘corn belt’ – could play a role. In Europe, small replacement habitats can often be found in the vicinity of agricultural land, ”explains Hochkirch. Nevertheless, it seems clear that something must be done to prevent bumble bee dying in this country too: “It is possible that the consequences of climate change can be mitigated by offering insects more habitats with protection from the heat like trees. Ultimately, however, we have to tackle global warming ourselves. The faster the better, ”emphasizes Soroyes colleague Jeremy Kerr.
Extinction risk at a glance
The scientists believe that the method they developed can also be used to draw conclusions about the endangerment status of other species. Using the temperature tolerances of individual species that have been observed in the past, they were able to predict relatively precisely where climate change caused conditions that the bumblebees cannot withstand. “With our approach, we were able to surprisingly accurately predict changes for individual species as well as entire bumblebee communities,” says Soroye. A similar method could therefore be used to estimate the extinction risk of reptiles, birds and mammals. For example, areas could be identified in which nature conservation measures are necessary and useful.
Source: Peter Soroye (University of Ottawa, Canada) et al., Science, doi: 10.1126 / science.aax8591