Intensive land use by humans affects the pollination of wild plants and their reproductive success worldwide, as a study has now confirmed. It shows that many wild plants in urban and intensively agricultural areas produce fewer seeds and fruits than they could. The researchers see the main cause as the decline in pollinating insects.
Plants provide important resources such as food and shelter for many other living things on earth. Most of the plants, however, depend on pollinators for their reproduction. These mostly include insects that fly to the flowers of the plants and distribute the pollen. Evolutive developments sometimes even lead to certain insects and plants specializing in one another, and pollination thus only depends on one species of insect. This occurs, for example, with some orchid species.
How badly does the decline in pollinators affect the plants?
But in recent years, studies have revealed that the abundance and numbers of pollinating insect species have dramatically decreased in many areas of the world. So far, however, little was known about which plants are particularly affected by this decline. How closely land use, the decline in insects and the reproductive success of plants are related was only partially clear. Because the effects on different pollinating animals are not always the same: while some farming practices can be beneficial to honeybees, they can lead to a decline in other pollinators such as wild bees and butterflies.
To establish a connection between land use and pollination success, an international team of researchers led by Joanne Bennett from the German Center for Integrative Biodiversity Research (iDiv) in Halle carried out a large-scale study. To do this, the scientists analyzed thousands of previously published studies on experiments in which plants were pollinated by hand. Such experiments compare how many seeds are produced by plants that have been pollinated naturally and how many seeds are produced by hand-pollinated plants. “If the plants that have been pollinated naturally produce fewer fruits or seeds than the plants that have also been hand-pollinated, then the reproduction of these plants is restricted,” says Bennet.
Bennet and her team used the results to create a global data set that shows the extent to which the reproductive success of wild plants is restricted due to a reduced uptake of pollen – and in which environments.
Cities and agricultural landscapes hardest hit
The result: wild plants in intensively used landscapes, such as in cities or many agricultural landscapes, are already severely restricted in their pollination. Plants that specialize in a narrow range of pollinators are particularly affected. However, there are differences – depending on the type of land use involved and which pollinators the plants have specialized in. Pollination of wild plants that specialize in bees as their pollinators was less restricted in agricultural areas than that of plants that specialize in other pollinators.
The results of the study suggest a link between intensive land use and lower reproductive success of plants due to decreased pollination. Future changes in land use could lead to a further decrease in pollination of plants. In addition, the plant diversity could be limited to species that are not very particular about their pollinators. “The relationships between plants and their pollinators have evolved over millions of years. People are now changing these relationships within a few years, ”says Bennet.
Source: German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig; Technical article: Nature Communications, doi: 10.1038 / s41467-020-17751-y