There are more than 570 species of wild bees in Germany. About half of them are threatened with extinction. It can be observed worldwide that the biodiversity of insects and thus the number of pollinating insects is declining. This also has consequences for the plants, which depend on pollinators. In a Study in the journal Nature Biologists and ecologists have now shown how competition for pollinators could affect the coexistence of different plant species.
Neighboring plants are in constant competition with each other: they compete for space, light, water and nutrients. When the pollinating insects become scarce, they also have to fight for the attention of the animals on which they depend for their survival. Using field trials in Switzerland, a research team led by Christopher Johnson from the Department of Ecology and Evolutionary Biology at Princeton University investigated competition for pollinators using five annual flowering plant species. Some of the experimental plots, each planted with two plant species, were naturally pollinated, so the species competed for pollinators. The comparison group was dusted by the researchers themselves with brushes. In this way, the coexistence of the plants could be investigated both with and without competition for pollinators.
Half of all flowering plants depend on pollinators
Whether plant species can coexist depends on various factors. In addition to the so-called fitness factors, i.e. the ability of the plant to produce seeds and reproduce, the differentiation from other species also plays a role. “When there is competition among plants, they look for different niches,” says Mark van Kleunen, Professor in the Department of Biology at the University of Konstanz. For example, one plant roots shallow below the surface to take up nutrients from the upper layers of the soil, while a neighboring plant species roots particularly deep and takes up the same nutrients from deeper layers of the earth.
The results of the new study show that if plants have to compete for pollinators, the proportion of plants that can coexist in the long term is reduced. Plants that are less frequently visited by pollinators than their neighbors are dwindling. The results confirm the researchers’ assumption that a lack of pollinators can destabilize competition between plants and thus endanger biodiversity.
The results of the study showed that the chances of the examined plant species coexisting are reduced by competition, says van Kleunen. However, it is difficult to transfer this to all plants. A large-scale study using data from different regions of the world, the 2021 in the specialist journal Science Advances appeared, but shows the enormous importance of pollinators for the survival of a large number of plant species. The scientists discovered that around 175,000 species, a good half of all flowering plants, depend predominantly or entirely on animal pollinators for their reproduction. According to the researchers, a decline in pollinators could also lead to a greater spread of self-pollinating plants, which in turn would offer less nectar and pollen for the remaining insects. “This creates a dangerous spiral,” says van Kleunen, who worked on the older study. “One can already observe that plants that are currently spreading are usually not so heavily dependent on pollinators.”