Do pollinators prefer dense flowers? Sometimes Yes, Sometimes No

A study looking at flower density and pollinators reveals that some types of pollinating insects prefer dense flowers more than others, but this preference can also vary among flower species. The complicated findings offer clues as to how several species of pollinators coexist and compete for floral resources. Shown here is a patch of Fistulous monarde, one of the flower species included in the study. (Photo by Joshua Mayer via Flickr, CC BY-SA 2.0)

By Andrew Porterfield

Andrew Porterfield

Andrew Porterfield

Historically, entomologists have concluded that bees and other pollinators select flowering plants based on the density of those plants in a given location. This makes some economic sense, as foraging in large areas of the same flowers reduces flight time (and therefore energy) between flowers.

But other research has shown that pollinator visits do not decrease when isolated from plants of the same species, suggesting that flowers in dense formations compete for pollinators. Understanding how pollinators are attracted to plants is important for seeing how different species of bees can coexist in the same pollen-producing environment.

In a study published in December in Environmental entomology, Tristan Barley, a student at the University of Miami in Ohio (now at the University of Illinois), and his colleagues found a large degree of variation in pollinator attendance when analyzed simply by the density of flower plates. Instead, the type of flower seemed to have an effect on pollinator attendance, as did the type of pollinator.

In their study, the researchers examined the effects of flower density on pollination in a restored Ohio prairie. They recorded visits to three species of plants: Penstemon digitalis, Monarda fistulosa, and Eryngium yuccifolium. Pollinators have been observed when they land on a flower, search for flowers, or visit multiple flowers on the same plant. The pollinators observed included species of Bombus, Ceratina, and others.

The importance of the identity of the flowers on the density, in particular for Ceratina, was a surprise, says Barley.

“This group of pollinators was the only one that was an important visitor to our three focal flower species, and yet the density of the flower plots affected their visit rates in different ways,” he says. ” During the visit Penstemon digitalis Where Fistulous monarde, both of which were also visited significantly by Bombus in our dataset, Ceratina tended to visit single flowers more often or even show no preference in the density of spots. However, the opposite was true when visiting E. yuccifolium. It appears that the identity of the flower visited, as well as potentially other pollinators visiting the flower, have a strong effect on patch size preference in some bee species.

For Bombus, bees seemed to generally prefer larger patches of flowers. The authors note, however, that “nesting habitat may contribute to these results, because Bombus species may preferentially nest in higher density flower patches compared to solitary bees. It is also possible that Bombus reduced flight time and energy costs by visiting larger groups of flowers.

The biggest implication of their research, according to Barley, is the possible mechanism that bee species use to coexist in the face of varying flower densities. “Larger, more social bees, like bumblebees, tended to visit larger flowered plots more than single flowers, while for smaller, less social bees, this was not the case,” he says. he. “Bumblebees may outperform small bees in larger flower patches, but smaller bees may be able to meet their energy needs by visiting single flowers instead. “

Because the researchers were only studying wild (native) bees in a plot of non-agricultural land, they were unable to determine the impact, if any, of Apis mellifera, the European bee. “Our results suggest that A. mellifera could compete more directly Bombus species when present in a habitat, rather than smaller native bees, ”which can avoid competition altogether, says Barley. But such interactions would only take place if honey bee colonies were deliberately placed near such a meadow.

This coexistence could help determine to what extent pollinators might occupy a given area. The concept, says Barley, “to our knowledge, has not been fully explored, and it could help future researchers better understand how diverse bee communities can coexist despite the sharing of floral resources.”

Andrew Porterfield is a writer, editor and communications consultant for academic institutions, businesses and non-profit organizations in the life sciences field. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.

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