Bumblebees seem to benefit from urban life: the insects are larger in urban regions and have better pollination performance than their counterparts in rural areas, a study has revealed. The cause of these changes in the urban bumblebee could be the greater fragmentation of the habitats in the cities and the often more diverse food supply. The scientists speculate that the urban climate could also play a role.
In the last 200 years, the habitat of many insects has changed significantly: They live less often in rural regions and on meadows, but are often surrounded by streets and concrete walls. “Cities have advantages and disadvantages for bumblebees: On the one hand, there is a plentiful supply of food through private and botanical gardens, city parks and balconies decorated with flowers,” says Panagiotis Theodorou from the Martin Luther University Halle-Wittenberg (MLU). “On the other hand, it is significantly warmer in cities than in the surrounding areas. In addition, streets and large buildings create significantly smaller, more or less strongly separated living spaces. “
Are city bumblebees different?
Does the changed habitat have consequences for the evolution of the bumblebees? Or can they possibly adapt to it? To study the effects of urbanization on insects, Theodorou and his colleagues carried out a study comparing bumblebees from rural and urban regions. To do this, they collected more than 1,800 bumblebees in nine large cities and their rural surroundings. The work focused on three common species in Germany: the stone bumblebee, the acker bumblebee and the dark bumblebee. Every bumblebee caught was measured.
The result: “In fact, the bumblebees from urban, more fragmented areas were on average significantly larger than their conspecifics in rural areas, by around four percent,” says Theodorous colleague Antonella Soro. These differences were evident in all three species of bumblebee. In addition, the research team observed at each of the 18 locations how often bumblebees visited red clover plants that were specially grown and released on site. From this, the scientists then calculated the insects’ pollination performance.
Larger bumblebees are better pollinators
The comparison showed that the higher the size of the bumblebees, the higher their pollination performance. The researchers believe that one of the reasons for this connection is that size affects the metabolism and lifespan of living things. “Larger bumblebees can see better, learn better, and have better memories,” says Soro. “They are also less likely to be attacked by predators and can travel further distances. This means that they can fly to more flowers per flight, transport more pollen and are therefore better pollinators. “
But what is causing urban size growth? As Theodorou and his colleagues report, their study provides initial indications that the degree of habitat fragmentation in particular could have an influence on the body size – and thus also on the pollination performance – of bumblebees. The diverse food supply, for example in private gardens and city parks, and the warmer temperatures could lead to evolutionary adaptations of the insects.
In general, however, too little is known about the effects of environmental changes in cities on the various bumblebee and bee species and their pollination performance, according to the scientists. The team therefore advocates better researching the evolutionary adaptations of animals to their urban environment. This could also enable more sustainable urban planning that takes more account of nature.
Source: Martin Luther University Halle-Wittenberg; Technical article: Evolutionary Applications, doi: 10.1111 / eva.13087