For over 60 years, scientists have tried to determine whether plants are pollinated primarily during the day or at night - without reaching a clear conclusion. Now, a major research review from Lund University in Sweden has revealed that nighttime pollinators play just as significant a role as daytime species in 90 percent of the cases studied.
Most of us know how important bees, birds, and butterflies are for plant reproduction - without pollinators, we would struggle to put food on our tables.
Less attention is given to the pollinators of the night, that is, bats, moths, and nocturnal butterflies; who are active while most of us are sleeping. Not only do they receive less recognition for the important work they do, but they also aren't protected in the same way as their daytime counterparts.
The question of the importance of nocturnal pollinators caught the interest of Lund researchers Liam Kendall and Charlie Nicholson when they stumbled upon studies that explored how individual plant species are pollinated during the day versus at night . They suspected that nighttime pollinators might have been overlooked in research.
More flexibility than expected
In a global meta-analysis, published in the scientific journal Ecology Letters, they can now show that nocturnal pollinators appear to play an equally important role.
The researchers compiled data from 135 studies worldwide - all they could find in the field - and found that 90 percent of the 139 plant species examined had similar reproductive success, regardless of whether pollination occurred during the day or at night.
"We were definitely surprised by the number of plant species where it didn't matter. We found this really fascinating because it's easy to assume that a specific plant needs a specific pollinator. The analysis actually showed almost the opposite - there's much more flexibility. A different pollinator than expected can contribute enough for a plant species to reproduce," says Liam Kendall, researcher at Lund University.
First meta-analysis of its kind
This global meta-analysis is the first of its kind, and the researchers argue that the study's results raise questions about human biases in science. Liam Kendall's hypothesis is that many have likely been stuck in a certain idea of how pollination for a particular plant should occur. He also speculates whether the fact that most people are active during the day affects this - possibly causing us to overlook what happens at night.
"We have this idea that all the magic happens during the day, because that's when we're active, and that's when we see bees and butterflies fluttering around flowers," says Liam Kendall.
He also believes the fact that daytime pollinators are often seen as beautiful plays a role.
"Bees are such a big part of our cultural identity. We learn that they're important. And they're fluffy and cute to look at. While moths - I mean, they have their prettier cousins, the butterflies, which we love, but moths are gray and dusty, and they eat your clothes. How could they possibly do anything positive?" says Liam Kendall.
More action needed to protect night pollinators
Given the pressure on biodiversity due to human activity, the researchers argue that their study highlights the importance of considering both nocturnal and daytime pollinators in agriculture and conservation. Liam Kendall mentions, for example, that a moth's life cycle from larva to adult is entirely different from that of a bee, and that their ecological needs are therefore different.
"The analysis shows that we need to change the way we think about how environments can support pollinators and biodiversity," says Liam Kendall.
If nighttime pollination is this important, it also becomes more crucial to avoid light pollution - that is, excessive or poorly placed lighting that disrupts the natural environment.
Other practices may also need to change.
"Actions are often taken to protect daytime pollinators, such as spraying pesticides at night. There's an oversight there - sure, you're protecting the daytime insects, but you're also, theoretically, harming the nocturnal pollinators. This means we could be doing much more, but we haven't thought enough about it so far, and more research is needed," concludes Liam Kendall.
