Fewer bee species have been recorded since the 1990s, raising concerns that rare species might be extinct.
About 25% fewer species were found between 2006 and 2015, compared to records prior to the 1990s, according to a study published on 22 January in the One Earth Journal. The authors are researchers at Argentina’s Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).
“Something is happening to the bees,” said biologist Eduardo Zattara, the report’s first author. “It's not a bee cataclysm yet, but what we can say is that wild bees are not exactly thriving.”
Wild and managed bees are essential pollinators that ensure the reproduction of thousands of wild plant species and 85% of all cultivated crops. Mounting reports show that the decline in wild bee populations might follow, or even be more pronounced, than declines in insect populations. Many animal populations are decreasing drastically, scientists have recently warned.
Sightings of rarer types of bees have fallen more sharply than those of more common families, researchers found. Records of Melittidae, a bee family found in Africa, have gone down by as much as 41% since the 1990s, while Halictid bees, the second-most common family, have declined by 17% during the same period.
Most bee studies focus on declining populations focus on a specific area, or on a particular type of bee. Instead, CONICET researchers examined the number of species recorded around the world over more than a century.
To do that, they used the Global Biodiversity Information Facility, an international network of databases that contains over three centuries of records from museum specimens, universities and geotagged smartphone photos shared by amateur naturalists in recent weeks. The network accounts for over 20,000 known bee species all over the world.
The results are subject to some uncertainty mainly because of the variety of data sources, making it impossible to reach definitive conclusions on individual species, researchers said. Technology has allowed for the recording of higher numbers of bees, but fewer species are being seen. Even accounting for possible distortions on the data, the trend is clear and matches that of previous, narrower reports.
“Given the current outlook of global biodiversity, it is more likely that these trends reflect existing scenarios of declining bee diversity,” the report said. “In the best scenario, this can indicate that thousands of bee species have become too rare; under the worst scenario, they may have already gone locally or globally extinct.”
Researchers conducted similar analysis on other insects to see if variations in bee species numbers were mirrored elsewhere, which would have been an indication that the changes had to do more with data collection and sources than with actual trends.
The populations of two wasp families also appear to be declining, but presented different patterns than bees’. Ant species, in contrast, have increased over the same period of time.
“We cannot wait until we have absolute certainty because we rarely get there in natural sciences,” Zattara said. “The next step is prodding policymakers into action while we still have time. The bees cannot wait.”
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