Flowering plants are better pollinated in urban than in rural areas. This has now been demonstrated experimentally by a team of scientists led by the German Centre for Integrative Biodiversity Research (iDiv), the Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Centre for Environmental Research (UFZ). Although the scientists found a greater diversity of flying insects in the countryside, more bees in cities resulted in more pollinated flowers of test plants. By far the most industrious pollinators were bumble bees, most likely benefitting from the abundant habitats available in the city. To promote pollination, the researchers recommend to take into greater account the needs of bees when landscape planning -- both in cities and in the countryside. Their results have been published in the journal Nature Communications.
Cities all over the world are expanding. A number of studies have already shown that the conversion of natural areas into built land affects insects and, while the diversity and abundance of insects often decrease, some insect species or species groups may benefit. However, little is known about the effects of urbanization on the ecosystem services insects provide, such as plant pollination.
A team of scientists led by the German Centre for Integrative Biodiversity Research (iDiv), the Martin Luther University Halle-Wittenberg (MLU) and the Helmholtz Centre for Environmental Research (UFZ) have now investigated the effect of the urban environment on insect pollinators and pollination. For this purpose, flower-rich, inner-city locations such as parks and botanical gardens were compared with similarly flower-rich sites in rural areas surrounding nine large German cities; Berlin, Braunschweig, Chemnitz, Dresden, Göttingen, Halle, Jena, Leipzig and Potsdam. The scientists sampled flying insects using pan-traps and potted red clover plants as reference for pollination in all locations. Furthermore, they also recorded all insect visits to red clover flowers 20 times a day for 15 minutes. The seeds produced were also counted, thus determining the rate of pollination success.
The most successfully pollinated plants were in the cities; here the flowers were visited more often than in the rural areas. Although the researchers found a greater biodiversity and biomass of flying insects in the rural areas -- especially flies and butterflies -- these did little to pollinate the red clover. This job was done predominantly by bees, which showed higher species richness and flower visitation rates in cities. Indeed, three out of four of the recorded flower-visitors were bumble bees. At a frequency of 8.7 percent, the honey bee was the second most important pollinator.
(Source: Agriculture and Food News, ScienceDaily. www.sciencedaily.com)