Wednesday, July 15, 2015

Bumblebee populations in steep decline due to climate change in North America and Europe


Bumblebee populations in North America and in Europe are in steep decline and shrinking their ranges due to human caused climate change says new research. The study was conducted across two continents based on over 110 years of data and observations.

This has enormous implications for pollination and eco-system health, as well as for human agricultural productivity. Many trees and plants are dependant to varying extents for reproduction and fruit on pollination by insects including bumble bees.

What was thought to be just one of several factors affecting wild and domesticated bee populations, is now seen to be far more important. Factors affecting the decline of bee populations include Colony Collpase disorder, use of pesticides including neonicotinoids, habitat loss, low genetic diversity and high infection rates with the parasite pathogens, and climate-driven mismatch between the times when flowers open and when bees emerge. (See my 2011 article: A dangerous sting for agriculture: climate change implicated in bee decline)

While many species have been noted as moving north or to higher elevations to match their climate envelope as temperatures increase (See Species biodiversity under threat from the velocity of climate change) , bumblebee species are not behaving the same or as expected. On southern boundaries and the hottest parts of their range bumblebee populations are disappearing, which is expected.

But populations are not expanding on the northern boundary of their range where weather conditions are warming due to climate change. In fact, many Bumble bee species have also been suffering a sharp decline in population numbers.

“One of the important things to me was how many species are being impacted by climate change. That was a bit of a surprise,” says York University Professor Laurence Packer, an expert on bees and a co-author on the study. “I’d suspected some may be declining, but not such a large proportion. The fact that at the northern edges of their ranges they are not moving north as the climate changes is actually really quite worrying.”

Much of the research was based upon large collections of bumblebees, hundreds of thousands of records, held by museums with detailed location and time of collection information stretching back over the last 110 years.

“Museums hold the basic biological information that tells us about the history of our impact on the world. They also contain the specimens that everything ultimately has to be compared to in order for identifications to be reliable,” Said Laurence Packer.

The researchers evaluated a number of other factors including land use change and pesticide use and found no significant correlation with these factors. While these factors may be important in explaining decline in some species and in local populations of bees and other pollinators, they do not explain the wholesale losses of bumblebee species being seen on two continents.

"The rates of loss are unprecedented in terms of there geographical extent and the magnitude of those loses." said lead author Jeremy Kerr from Ottawa University.

About a third of bumblebee species in North America are in decline, says study co-author and York University environmental studies Professor Sheila Colla, and “in some cases this has been quite dramatic, over 90 per cent."

"Historically they were quite common, among the most common bees. The Rusty Patched bumblebee in particular was the fourth most common bumblebee in southern Ontario as recently as the 1970's or early 80s, but I have only seen two individuals in 10 years. That is an indication there is something going on with bumblebees that used to be doing quite well but have recently collapsed."

The extent of the recent decline and it's rapidity is one of the things that has shocked the scientists.

“One of the scariest parts of the work that I’ve done is just realizing how quickly the situation is changing. The bumblebees that are in decline were doing fine 50 years ago. We’re talking about large changes in community composition of essential pollinators over just a few decades.” said Colla.

"So the consequences of losses of pollinators over large areas is both economic but also practical in terms of diminished food security and in terms of rising food prices. We need to get a handle on climate change once and for all." said study lead author James Kerr from the University of Ottawa.

This raises important issues for food security as pollination is an essential service for agricultural productivity. According to Bauer and Wing (2010) in their study - Economic Consequences of Pollinator Declines: A Synthesis - they wrote:

"At the global level, 75 percent of primary crop species and 35 percent of crop production rely on some level of animal pollination (Klein et al. 2007). Gallai et al. (2009b) estimate the value of this pollination service to be €153 billion (~$200 billion). In the United States, more than half of primary crop species and 20 percent of primary crop production rely in part on animal pollination. A recent study estimates the value of honey bee pollination alone in the United States at $14.6 billion, which reflects both direct crop and indirect livestock feed values (Morse and Calderone 2000)."

Indeed. Professor Nigel Raine, Rebanks Family Chair in Pollinator Conservation at the University of Guelph in Canada, commented on the impact on agriculture: "Bumblebees are critical pollinators of many crops and wild flowers, so it is very concerning that they are struggling to adapt to climate change around the world. We urgently need to understand how other pollinators critical for fruit and vegetable production are being affected by climate change."

The study identified that there had been range losses of up to 300 kilometers in both North America and Europe.

But more research is needed to figure out why bumblebees have not shifted their boundaries further north as the climate has warmed. Assisted migration and translocation of bumbelbee populations northward is seriously being considered to artificially prevent loss of species and extend population range to attempt to mitigate the decline.

The research was conducted by 14 scientists from Canada, USA and Germany and published in the peer reviewed journal Science as Climate change impacts on bumblebees converge across continents. The abstract states:

For many species, geographical ranges are expanding toward the poles in response to climate change, while remaining stable along range edges nearest the equator. Using long-term observations across Europe and North America over 110 years, we tested for climate change–related range shifts in bumblebee species across the full extents of their latitudinal and thermal limits and movements along elevation gradients. We found cross-continentally consistent trends in failures to track warming through time at species’ northern range limits, range losses from southern range limits, and shifts to higher elevations among southern species. These effects are independent of changing land uses or pesticide applications and underscore the need to test for climate impacts at both leading and trailing latitudinal and thermal limits for species.


Jeremy Kerr, in a Youtube video, explained the importance of the results of climate change impacts on bumblebees. Here is a full transcript I made of the video:


We are very exited about the findings we are reporting in this paper in Science, at the end of this week. What we are going to report on is the discovery that bumblebee species across Europe and North America are declining at continental scales as a function of rapidly changing climatic conditions, and that is changing climatic conditions that reflect human activity.

The rates of loss are unprecedented in terms of there geographical extent and the magnitude of those loses.

We have seen decline of bumblebee species as their geographical range collapses inwards because of rapid warming on the scale of hundreds of kilometres.

To do this work we looked at more than a century of observations for 68 species on both continents. These observations give us a pretty comprehensive look at the precise distribution for each one of those species through time and across continents.

We have also been able to measure how environmental conditions change in both Europe and North America with respect to a few different factors that are potentially very important for causing bumblebee ranges to shift around. Among these factors is climate change which we knew could be significant, but which we didn't think was going to be as significant as it has been.

But also how habitats have changed across continents and how in some areas rapid increases in pesticide and neonicotinoid insecticide use has changed. What we are seeing is that neither habitat loss or pesticide use is able to explain how the geographical ranges of these species are collapsing inward. Instead, the only factor that appears able to explain this trend is rapid warming along boundaries of species geographical ranges.

The consequence here is that we are seeing wholesale losses of bumblebee species from places they used to be common but have become too hot to maintain populations.

We have also observed, and again this is a first, that these species have been unable in general to expand their ranges into northern areas that used to be too cold for them.

Other groups, like butterflies, have proven to be pretty good at expanding towards the poles in terms of their geographical distributions, the net effect being that as climate changes the geographical ranges for many butterfly species actually gets bigger.

For bumblebee species, the exact opposite trend is underway. As rapid warming proceeds, the ranges collapse inward. The consequence is that pollinators are declining over huge areas, and in the particular way we have measured it here, those effects reflect climate change, but they do not reflect habitat losses or pesticide use, although those factors can certainly be important in some areas and for some species.

We have also been able to track how the geographical ranges of these species have shifted along elevation gradients, and those results mirror the results we have observed across continents quite well, giving us additional confidence that our results probably are sound.

We have done one more thing here that is very unusual in terms of research at this kind of level, and that is we have made all our data and analytical techniques publicly available. So that as the paper is published anyone in the world will also be able to download all of our data and reproduce and evaluate all the results that we have reported on and this paper to Science.

We are very excited by these findings. We think we are now in the position to make specific management recommendations that we hope will enable us to mitigate some of the worst effects of climate change on these bumblebee species.

One of the things we are going to need to contemplate is what is known as assisted migration, where we transplant populations of bumblebee species a little further north and to places where historically they are not present in but where we think they need to go in order to maintain themselves. Our results suggest this may be necessary for large groups of species across continents.

Moreover, the critical message here is that we need to get a handle on climate change. The effects are rapid and well under way and they began at least 20 or 30 years ago. It is only now where we are assembling enough data to detect some of those impacts. It would be impossible to expect anything else at this stage than that these effects will continue and probably become more and more extreme with time.

So the consequences of losses of pollinators over large areas is both economic but also practical in terms of diminished food security and in terms of rising food prices. We need to get a handle on climate change once and for all.



There have been previous indications that several bumble bee species have suffered a severe decline in population and range. I last reported on the decline in bee population and ranges in 2011. That article lead with an in depth national study of wild bees in the United States (Cameron et al 2011) that concluded that the relative abundances of four of the eight species analyzed had declined by as much as 96 percent and that their surveyed geographic ranges have shrunk by 23 to 87 percent. At least some of this decline had occurred in the last two decades.

The study - Patterns of widespread decline in North American bumble bees - suggested that significantly higher infection levels of the microsporidian pathogen Nosema bombi and lower genetic diversity were important determinants in the decline, although other factors were not ruled out. See A dangerous sting for agriculture: climate change implicated in bee decline.

University of Illinois entomology professor Sydney Cameron, who led the study, published in 2011, said at the time that Climate change may play a role, as well as habitat loss, low genetic diversity and high infection rates with the parasite pathogen. "Whether it's one of these or all of the above, we need to be aware of these declines," she said in a media release.

The most recent study indicates that climate change factors are of far greater importance, but with still many questions still to be answered by further research on wildlife response to climate change and impacts on ecosystems.

Dr Nathalie Pettorelli, Research Fellow, Zoological Society of London (ZSL), highlighted that the study was very robust and triggers important questions on wildlife response to climate change. "I think it’s important to remember that this type of correlative approach is aimed at unveiling large scale patterns in species’ response to climate change, and that it needs to be followed by new process-based research." she said.

“Kerr et al show that bumblebees generally fail to track warming in both Europe and North America: the next step is to understand why. Without this knowledge, efficient mitigation strategies are difficult to identify. I would also add that there seem to be some interesting level of variation in bumblebee species’ response to changes in climatic conditions, something that isn’t discussed in the paper. This level of inter-specific variability might be important to consider when thinking about mitigation strategies, as one solution might not fit all.” she commented.


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