Plant diversity depends on pollinators

About half of all seed plants depend predominantly or entirely on bees, butterflies and other animal pollinators for their reproduction. The number of these animal-dependent species is estimated by an international research team in the journal “Science Advances” at about 175. 000. The decline in pollinators threatens entire ecosystems and their plant diversity.

Most plants reproduce through pollination, in which pollen is carried from one flower to the next. A team of researchers from 23 institutions in five continents under the direction of James Rodger and Allan Ellis from the South African University of Stellenbosch.

Effects also on humans

Decisive for the importance of animal pollinators their contribution to seed production – measured by comparing seed production with and without pollinators. The data required for this was available, but it was spread over hundreds of studies that focused on pollination experiments with different plants.

The team is summarizing this information in a global database. This contains information from more than 1500 tests with just under 1400 plant populations and around 1200 species from 143 plant families.

The results show that without pollinators one third of the 350. 000 Species of seed plants would not produce seeds at all, half would suffer a decrease in fertility of at least 80 percent. Although many plants are able to self-pollinate, in most species this by no means compensates for the decline in pollination performance.

“Studies show that many pollinator species have declined and some have even become extinct” , says lead author Rodger and warns: “Our finding that a large number of wild plant species are dependent on pollinators shows that their decline could cause major disturbances in natural ecosystems.”

Persistent threat to pollinators in Europe

Co-author Mark van Kleunen from the University of Konstanz adds that the consequences of such a decline do not only affect plants. Rather, animal species that are dependent on these plants and ultimately humans would also suffer.

The world’s first inventory of pollinators by the World Council for Biological Diversity (IPBES) already showed 2016, how important they are for human food security: Between five and eight percent of global agricultural production depends on this type of pollination. The resulting food has a value of 235 to 577 billion US dollars (204 to 500 billion euros).

Two years later, the European Commission decided on a package of measures to protect pollinators, but this is only slowly taking effect. According to a report from May 2021, the establishment of an EU-wide system to monitor species and their decline is proceeding successfully. However, nothing has changed in the numbers since the start of the EU initiative: every tenth species of bees and butterflies in Europe are still threatened with extinction, and a third are shrinking populations. More needs to be done against habitat loss and the effects of pesticides.

According to the current study, such measures are important not only with regard to crop production, but also for biodiversity. “Plants that do not depend on pollinators could spread even more if the pollinators continue to decline,” notes van Kleunen.

At the same time, a vicious circle could arise when plants dependent on pollinators decline or become extinct, explains Joanne Bennet from the University of Canberra: “When self-pollinating plants dominate the landscape, even more pollinators are negatively affected because self-pollinating plants tend to produce less nectar and pollen.”

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