Loss of Just one Bee Species Lowers Reproduction Success in Flowering Plants

A new study has found that plants reduce their seed production even if one of their favorite pollinators disappears. The study shows the complexity of the system.

The study was conducted by researchers from Emory University and their colleagues, who found that loss of even one species of pollinators reduces competition and affects the floral fidelity which further leads to lower reproduction success in plants. Researchers focused on the interaction between bumblebees and larkspur wildflowers in Colorado's Rocky Mountains in the current research.

Bees are known for their role in pollination of flowers- about 90 percent plants require insects to pass their pollen. There are about 4,000 species of bees in North America.

There has been a recent decline in the bee population around the world and experts say that loss of bees could threaten global agriculture.

Previously, other scientists had believed that plants can keep up with the loss of a few bee species as long as the other bees are around to pollinate them. These studies were mostly based on a theoretical computer model.

The present study, conducted on the field, found that the removal of one species of pollinators is enough to reduce the rate of reproduction in the plants. They found that bees display a kind of "floral fidelity" for short time, meaning that they visit the same species of flowers while they are blooming. This behavior of the bees increases the reproduction chances of the flowering plants, Brosi said.

Note that bees visit many different plant species. But, this kind of floral fidelity by some bee species that favor a particular plant opens a window of opportunity for that species of plants to increase reproduction.   

"We found that these wildflowers produce one-third fewer seeds in the absence of just one bumblebee species," said ecologist Berry Brosi, from Emory University, who led the study. "That's alarming, and suggests that global declines in pollinators could have a bigger impact on flowering plants and food crops than was previously realized."

The study was conducted at Rocky Mountain Biological Laboratory near Crested Butte, Colorado, which is located at about 9,500 feet. The location of the site makes it difficult for many honeybee populations to visit the flowers, but they can be found during the summer months. The flowers chosen for the study were dark-purple wildflowers called larkspurs that are visited by 10 of the 11 bumblebee species in the area.

The experiment included the researchers running around the bees to see which flowers they are pollinating. The experiment had a manipulated plot where the entry of just one species of bumblebee was restricted (by using a net to cover the plot) and a control plot where there was no restriction.

The researchers caught bumblebees of a particular species and swabbed them off of the pollen which prevented them from pollinating the flowers. The team said that they didn't harm any insects during the experiments.

The results showed that bees belonging to manipulated plots had lower floral fidelity compared with the control plot (66 percent versus 78 percent), meaning that the bees visiting the manipulated plot were carrying pollen from different species of plants.

This led to the reduction in the seed production of the larkspur- they produced one-third fewer seeds when one species of bumblebee was removed from the system.

"Our work shows why biodiversity may be key to conservation of an entire ecosystem," Brosi said in a news release. "It has the potential to open a whole new set of studies into the functional implications of interspecies interactions."

The study appears in the journal Proceedings of the National Academy of Sciences.