When we think about bees, the image that often comes to mind is the iconic honeybee, bringing you the oh-so-sweet honey that you use to flavor your tea or dab on your toast.
But there are more than 20,000 bee species worldwide, and the honey bee is just one of them. And for the first time, researchers have created a comprehensive map of these bees' distribution across the globe.
The map reveals where in the world bees are most diverse — and where they may be most at-risk of climate change.
The Big Picture — Using a combination of 6 million public records and a bee checklist compiled by study co-author John S. Ascher, the researchers compiled a wealth of data into the first such comprehensive look at the global distribution of bees.
The map was published Thursday in the journal Current Biology.
Interestingly, the map shows bee diversity as particularly rich in certain areas of the Americas, southern Europe, South Africa, and southern Australia. Unlike many animal species, which increase in diversity as you approach the tropics, bees seem to decrease in diversity near the tropical equator.
The new map provides valuable insight into bees and provides a significant resource to scientists looking for data on global bee diversity, which was sorely lacking compared to other animals, like birds.
"This is why it was so crucial that we had access to [the] global bee species distribution checklist," says Michael Orr, first author on the study and a postdoctoral fellow at the Institute of Zoology, Chinese Academy of Sciences.
"Together with [study co-author Alice C. Hughes'] methods, we were able to use these data to give us an unprecedented view of bee species richness despite the lacking public data."
Based on the number of species or "richness" of bees in certain regions — and the lack of diversity in others — the researchers were able to confirm previously held views about this essential pollinator. But the trend in diversity increasing away from the tropics ran against expectation.
"In the tropics there are many more flowering trees and they're much more important for bees there, but there are many potential issues with tropical areas for bees, including food spoilage due to the humidity, competition with highly-abundant eusocial bees like honey bees and stingless bees, and more," Orr says.
Survive and thrive — Rather, bees appear to thrive in drier climates near the Earth's poles, particularly in the Northern Hemisphere. A few key hotspots include the southwestern United States and the Mediterranean region.
Although, bees do need some rain, so completely dry environments won't cut it for them.
"Water is important not just for plants they need, but also for many bees as a cue of when to emerge," Orr says.
The research also highlights the various factors that shape bee diversity — like water, plant life and sunlight —and shows how these factors can vary widely depending on where you're looking and the scope of the area.
"This is critical knowledge because it shows that different factors drive bee distribution when you're looking at different places and sizes of areas, basically," says Orr. "So this gives an important caveat for future work, that you can't make assumptions about bee distribution and translate them across scales."
Most surprisingly, the team learned that while bees do well in most areas with greater plant life, they do not thrive in forested areas.
"In fact, a dense tree canopy blocks a lot of sunlight from reaching the ground floor below, and this can really hinder the growth of smaller flowering plants. As a consequence, in forested areas, we usually see highest bee richness within meadows where the trees are absent," says Orr.
It is important to note that there is a significant gap in data from certain parts of the world, especially Asia, Africa, and Australia — and so the map may miss a considerable number of bee species.
This is particularly true of China, which has the sixth-highest number of bee species in the world, but records only reflect seven percent of the country's bee species.
Next Steps — The study calls for a well-funded database of experts who could create and compare species checklists and build a better understanding of bees around the globe.
"We want to build higher-resolution models of bee species richness, as then we can start looking more directly at bee conservation, including possible human pressures, how effective current protected areas are for bees, and even how bees might be impacted by climate change," Orr says.
With bee species on the decline in parts of North America and researchers seeking to better understand native bees elsewhere, the global map that these scientists have provided will undoubtedly serve as a vital resource for tracking bees in the years to come, especially with the perils of climate change looming.
"There has been work on some bumble bees showing that they're likely to be strongly impacted by climate change for instance, but they are better known than most other bee groups," says Orr.
"The bottom line is that for most bees we just don’t know yet, and the first step is finding out where they live now, under present conditions."
Abstract: Insects are the focus of many recent studies suggesting population declines, but even invaluable pollination service providers such as bees lack a modern distributional synthesis. Here, we combine a uniquely comprehensive checklist of bee species distributions and >5,800,000 public bee occurrence records to describe global patterns of bee biodiversity. Publicly accessible records are sparse, especially from developing countries, and are frequently inaccurate throughout much of the world, consequently suggesting different biodiversity patterns from checklist data. Global analyses reveal hotspots of species richness, together generating a rare bimodal latitudinal richness gradient, and further analyses suggest that xeric areas, solar radiation, and non-forest plant productivity are among the most important global drivers of bee biodiversity. Together, our results provide a new baseline and best practices for studies on bees and other understudied invertebrates.