Bees, rightly, get a lot of attention these days, yet scientists know surprisingly little about where these animals live.
Now a pioneering study, just published in Current Biology, reveals that bees avoid moist, tropical ecosystems and instead prefer dry, treeless landscapes. The research shows the greatest diversity of species lives in two bands around the globe - mostly in temperate zones - which is described as an unusual distribution pattern.
Experts say this first-ever map of bee species around the world is a leap forward in understanding and protecting the pollinators that our food supply and ecosystems rely on.
“Humans are pretty good at just going for what's easy, which is why we've got really great data on mammals, but then we overlook all the invertebrates, despite the fact they contribute some really important services within ecosystems,” says Alice Hughes, associate professor at the Chinese Academy of Sciences and author of the paper. “If we don't understand what those patterns of diversity look like, we've got no means of trying to conserve them.”
Mapping animals of any kind on a global scale is a challenge, but when assessing tiny, similar-looking species with patchy data, the task is particularly daunting. The team looked at nearly six million public records of where bees appeared around the world from five publicly-accessible open source databases. They then compared that information with a comprehensive checklist of species compiled by entomologist John Ascher available in DiscoverLife, an encyclopedia of global species diversity.
“Bees aren't like birds - they're really hard to identify. You need really good taxonomists to do this,” says Cariveau. “And this paper, these authors, are really some of the best taxonomists in the world.”
Hughes and her colleagues also set standards for the quantity of the data used in each region to make sure the results weren’t weighted unfairly toward places with more records. She says the end result was a map that was as accurate as possible.
The research revealed that bee species were most numerous in two bands around the globe, with more species in the Northern Hemisphere - in areas including California, Morocco and the Himalayas - than in the Southern Hemisphere - in regions including South Africa and the Andes. While most plant and animal species are richest in tropical areas, bees avoid these ecosystems along with the colder areas near the poles.
This two-banded distribution is an anomaly, says Cariveau. “If you were to study beetles, or butterflies, or moths, or things like birds, you see this unimodal pattern where you get this increase in the tropics. So this is a really unique thing."
“Nobody has, to my knowledge tried to produce a map of bee diversity previously,” says Paul Williams, an entomologist at the Natural History Museum in London who was not involved in the work. “I think it's a fantastic move in the right direction.”
Williams says this work brings into focus what many bee researchers suspected from smaller-scale efforts to map the diversity of bees on local levels. Williams thinks the bees’ avoidance of tropical and forested environments likely has to do with food abundance and nesting choice. Most bees aren’t social honey-producers. They often live alone and don’t sting. And because many of these solitary species nest in the ground, the water-logged earth of tropical environments means fungi could spoil their food stores, threatening the bee’s survival.
With the impacts of climate change mounting, Cariveau says this work could point to bee habitat that needs protection now, and to areas bees might live in the future. “Whether the plant communities can migrate given climate change, whether bees can follow those I think, is a pretty interesting and important thing to be figuring out as we move forward,” says Cariveau.