Artificial light disrupts nocturnal pollination and leads to a reduced number of fruits produced by the plant.
This loss of night time pollination cannot be compensated by diurnal pollinators. The negative impact of artificial light at night on nocturnal pollinators might even propagate further to the diurnal community, as ecologists of the University of Bern were able to show.
The number of bees and other diurnal pollinators is declining worldwide – due to diseases, introduced parasites, pesticides, climate change and the continuing loss of habitats. Now, Eva Knop's team from the Institute of Ecology and Evolution at the University of Bern, shows for the first time, that nocturnal pollinators can be affected by artificial light leading to a disruption of the pollination service they provide. "So far, nocturnal pollinators have been largely neglected in the discussion of the worldwide known pollinator crisis", says Knop. However, there are numerous nocturnal pollinators, and they play an important role for plants, as the study in the Bernese Prealps shows. Knop’s team found out, that flowers on meadows which were experimentally illuminated with street lamps are visited around two thirds less frequently by pollinators, than those that were on meadows without any light sources in the vicinity. This has an effect on the fruit set, and therefore the reproduction of plants. The study has now been published in the magazine "Nature".
In the last 20 years, the light emissions have increased by 70%, particularly in residential areas. "As it is possible that light sensitive insects have already disappeared in regions with high levels of light pollution, we conducted our study in the still relatively dark Prealps", explains Knop. The researchers could show that during night a total of almost 300 insect species visited the flowers of around 60 plant species on ruderal meadows without any artificial light sources in the vicinity. Interestingly, on meadows with experimentally set up street lights, the nocturnal pollination visits were 62% lower than in the unlit areas. The LED lamps used, are used as standard for public street lighting.
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Image via Maurin Hörler, University of Bern