Pollinators are Essential for Seed Production in Plants, According to the First Global Estimate

About 175,000 plant species rely on animal pollinators to form seeds and reproduce, and half of all blooming plants do. Pollinator declines might thereby create significant disturbances in natural ecosystems, including biodiversity loss.

This is the finding from a paper, “Widespread vulnerability of plant seed production to pollinator declines,” published in the journal Science Advances on 13 October 2021.

This is the first study to offer a worldwide assessment of the value of pollinators for plants in natural ecosystems, according to Dr. James Rodger, a postdoctoral scholar in the Department of Mathematical Sciences at Stellenbosch University (SU) and main author.

Dr. James Rodger and Prof Allan Ellis of Stellenbosch University led the study, which included 21 experts from 23 universities across five continents (SU). It is a product of the German Centre for Integrative Biodiversity Research’s Synthesis Centre for Biodiversity Sciences (sDiv).

Prof Tiffany Knight, a senior co-author from the Helmholtz Centre for Environmental Research, says recent worldwide pollination assessments have shown a knowledge gap in our understanding of how dependent plants are on animal pollinators: “Our synthetic research addresses this gap, and enables us to link trends in pollinator biodiversity and abundance to consequences for plants at a global level,” she explains.

Recent studies show that many pollinator species have gone down in numbers, with some even having gone extinct. Our finding that large numbers of wild plant species rely on pollinators shows that declines in pollinators could cause major disruptions in natural ecosystems.

Dr. Rodger Warns

While most plants are pollinated by animals, they can exhibit some self-fertility. This implies plants can produce certain seeds without the need for pollinators, such as by self-fertilization. However, until this study, the question, “How important are pollinators for wild plants?” did not have a clear answer at the global level.

The researchers utilized pollinator contribution to seed production as an indication of their relevance to plants, comparing seed production in the absence of pollinators versus seed production with pollinators present. This information was available, but it was dispersed throughout hundreds of studies, each concentrating on pollination tests on various plant species.

To address this problem, researchers at various institutions started to consolidate the information in databases: Dr. Rodger developed the Stellenbosch Breeding System Database as a postdoctoral fellow in SU’s Department of Botany and Zoology; Prof Tiffany Knight, Prof Tia-Lynn Ashman, and Dr. Janette Steets led the sPLAT working group that produced the GloPL database; and Prof Mark van Kleunen and Dr. Mialy Razanajatovo produced the Konstanz Breeding System Database.

For the current investigation, all three databases were integrated into a single database. It contains data from 1 528 distinct studies, covering 1 392 plant populations and 1 174 species from 143 plant families, as well as data from all continents except Antarctica.

According to the findings, without pollinators, a third of flowering plant species would produce no seeds and half would have a fertility decrease of 80% or more. As a result, while auto-fertility is prevalent, it does not entirely compensate for pollination service losses in most plant species.

“Recent studies show that many pollinator species have gone down in numbers, with some even having gone extinct. Our finding that large numbers of wild plant species rely on pollinators shows that declines in pollinators could cause major disruptions in natural ecosystems,” Dr. Rodger warns.

Prof Mark van Kleunen, from the University of Konstanz and a co-author, says it is not a case of all pollinators disappearing: “If there are fewer pollinators to go around or even just a change in which pollinator species are most numerous, we can expect knock-on effects on plants, with affected plant species potentially declining, further harming animal species and human populations depending on those plants. Pollinators aren’t only important for crop production, but also for biodiversity.”

“It also means that plants that do not rely on pollinators, like many problematic weeds, might spread even more when pollinators continue to decline,” he adds.

Another concerning element, according to Dr. Joanne Bennet, a co-author from the University of Canberra who maintained the GloOL database, is the positive feedback loop that emerges if pollinator-dependent plants dwindle or go extinct: “If auto-fertile plants come to dominate the landscape, then even more pollinators will be negatively affected, because auto-fertile plants tend to produce less nectar and pollen.”

But, according to Dr. Rodger, it’s not all doom and gloom. Many plants survive for a long time, providing a chance to reintroduce pollinators before plant extinction due to a shortage of pollinators.

“We lack high-quality long-term monitoring data on pollinators in Africa for example, including South Africa, although some work has been started in this regard. We hope that our findings will stimulate more of this kind of research so that we can detect pollinator declines and mitigate their impacts on biodiversity,” Dr. Rodger concludes.