Most flowering plant species rely on pollinators to reproduce. Annual daisy species that dominate the spring mass flowering in South Africa.
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Decline of plant pollinators threatens biodiversity

Despite evidence of pollinator declines from many regions across the globe, the threat developments pose to plant populations is not clear because plants can often produce seeds without animal pollinators.

About 175 000 plant species – half of all flowering plants – mostly or completely rely on animal pollinators to make seeds and so to reproduce. Declines in pollinators could therefore cause major disruptions in natural ecosystems, including loss of biodiversity. 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.

Dr James Rodger, a postdoctoral fellow in the Department of Mathematical Sciences at Stellenbosch University (South Africa) and lead author, says, this is the first study to provide a global estimate of the importance of pollinators for plants in natural ecosystems.

The study, involving 21 scientists affiliated with 23 institutions from five continents, was led by Rodger and Prof Allan Ellis from Stellenbosch University (South Africa). It is a product of the Synthesis Centre for Biodiversity Sciences (sDiv) in the German Centre for Integrative Biodiversity Research (iDiv) in Halle-Wittenberg.

Prof Tiffany Knight, senior co-author, says that recent global assessments of pollination have highlighted a knowledge gap in our understanding of how tremendously plants rely 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,” maintains Knight, who heads the Spatial Interaction Ecology research group at Martin Luther University Halle-Wittenberg (MLU), the Helmholtz-Centre for Environmental Research (UFZ) and iDiv.

While most plants are animal-pollinated, they usually also have a bit of auto-fertility. This means they can make at least some seeds without pollinators, for example by self-fertilisation. However, until this study, there had been no clear answer at global level to the question of how pollinators are for wild plants.

The researchers used the contribution of pollinators to seed production – measured by comparing seed production in the absence of pollinators to seed production with pollinators present – as an indicator of their importance to plants. Data on this existed but were spread among hundreds of papers, each focusing on pollination experiments on different plant species.

To address this problem, researchers at various institutions started to consolidate the information in databases. Rodger developed the Stellenbosch Breeding System Database, 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 of  the University of Konstanz/Germany produced the Konstanz Breeding System Database. All three databases were combined in a new database for the current study. It includes data from 1,528 separate experiments, representing 1,392 plant populations and 1,174 species from 143 plant families and all continents except Antarctica.

The findings show that, without pollinators, a third of flowering plant species would produce no seeds and half would suffer an 80 per cent or more reduction in fertility. Therefore, even though auto-fertility is common, it by no means fully compensates for reductions in pollination service in most plant species.

"Our finding that large numbers of wild plant species rely on pollinators shows that declines in pollinators could cause major disruptions in natural ecosystems,” Rodger warns.

Pollinators are not only important for crop production, but also for biodiversity

According to van Kleunen, also a co-author of the study, 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," he says. “It also means that plants that do not rely on pollinators, like many problematic weeds, might spread even more when pollinators continue to decline.”

All is not doom and gloom, though, according to Rodger. Many plants are long-lived, opening a window of opportunity to restore pollinators before plant extinctions occur from lack 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,” Rodger concludes.

(Stellenbosch University/iDiv/wi)

Original publication:
Rodger, J. G., Bennett, J. M., Razanjatovo, M., Knight, T. M., Ellis, A. G. et al. (2021) Widespread vulnerability of plant seed production to pollinator declines. Science Advances, Vol. 7, No. 42. DOI: 10.1126/sciadv.abd3524

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