Bees perform a critical role as pollinators in the ecosystems humans depend upon for food. Unfortunately, climate change poses significant risks to the habitats of important organic elements of the food cycle such as bees. Given the prevalence of Colony Collapse Disorder and various vectors and pathogens already ravishing Europe’s continental bee populations, Roberts et al. (2012) seeks to assess extinction threats to six species of pollinating bees by projecting climatic changes across Europe through 2050. By modeling temperature changes and growth rates of key plant species, the researchers hope to better understand where, if anywhere on the continent, these bee species will be able to survive. This is the largest geographic area ever studied for an experiment of this kind; the continental scope allows researchers to compare local and distant climatic changes which they believe will assist in predicting migration patterns for threatened bee species. The study found significant risks posed by climate change in the coming decades to all six bee species researched.
Roberts, Stuart P.M., Potts, Simon., Biesmeijer, Koos., Kuhlmann, Michael., Kunin, Bill., Ohlemüller, Ralf., 2011. Assessing continental-scale risks for generalist and specialist pollinating bee species under climate change. BioRisk 6 1–18.
Roberts et al. selected six well-dispersed bee species in Europe, three of which were generalist species, meaning that they pollinate many different plants, and three of which were specialist species, meaning that they only forage for a specific plant. The researchers took 125 years of distribution data for the six bee species and organized it on a presence/absence map of Europe made up of 10’ grid cells. They also gathered distribution data for the chosen plants of the specialized species as well as records of climatic conditions from the past fifty years and predictions for the next fifty. Combining these data, Roberts et al. were able to create bioclimate models which determined the preferred climates of the six species in question. When they tested the model in present conditions, its results overlapped closely with the actual bee populations. By 2050, the model predictions showed all six species suffering severely curtailed local and continental suitable habitats. One species, C. impunctactus, was predicted to have little to no suitable climate in all of continental Europe by 2050.
An interesting component of this project was the testing of both generalist and specialist species of bee. Given that the specialist forage plants are widely distributed across the continent, Roberts et al. conclude threats to bees are not related to specialization. Rather, the major common threat to all six species is a severe reduction in climatically suitable ranges and growing isolation between these shrunken ranges. Most dramatically, the aforementioned C. impunctatus would have to travel over 100 km to find any climatic region in which they could conceivable live. For the specialist species C. Wolfi, 70% of regions local to its current location will become uninhabitable, however most of Europe will remain habitable if the species manages to disperse. In the best case, the model predicts two of the specialist species, C. anchusae and C. hederae should have significant local and continental habitats still suitable by 2050. Even though the latter two species might fair better, all six face increased isolation which could negatively impact rates of pollination.
While Roberts et al. argue that greater research is required to generate a fuller understanding of climate change on pollination, they do offer a few conclusions from their research into six species of bee. They demonstrate the strong likelihood that decreased populations and increased isolation will become more common as temperatures raise through 2050. It seems logical to suggest that many more of Europe’s 2,250 species of bee could also be at risk from climate change. One possible consequence of a decline in suitable climatic regions could be the spread of parasites as colonies are forced to migrate. Two of the species studied are believed to be transmitters of parasites. A spread of vectors could significantly decrease the already dwindling bee populations, even in areas with suitable climates.