Previous studies may have been underestimating the number of bee species needed for adequate pollination by at least one order of magnitude, a new large-scale effort finds. The results help to disentangle the influences of species dominance and species turnover (the replacement of one species for another across space or time) on ecosystem functioning. Many studies to date have explored the influence of biodiversity on ecosystem functions, such as nutrient cycling and pollination. However, whether the findings of field and laboratory experiments truly apply to natural systems is debated. In particular, the question of just how many pollinators are needed to ensure successful crop pollination on large scales remains unknown.
To gain a better understanding of the impacts of bee diversity on widespread pollination, Rachael Winfree and colleagues studied crop pollination by wild (unmanaged) bees at 48 commercial crop fields in the Mid-Atlantic region of the United States and measured the typical amount of pollen that each species delivers on a single visit. They found that at the smallest spatial scale, achieving the 50% pollination threshold required 5.5 bee species; however, achieving the 50% threshold across all 48 sites required 55 bee species.
Modeling revealed, surprisingly, that the effects of species turnover were, on average, 14 times more important for pollination function than were the effects of species dominance (at the largest scale of analysis). These results highlight how sites with low levels of pollination will require most or all of their species, including the rare ones, to reach a sufficient pollination threshold.
Claire Kremen discusses these findings in a related Science Perspective article , noting that the re
sults of this study may help support the idea that conservationists should use ecosystem-service arguments “to garner support from a broader array of people for biodiversity conservation.”
This research appears in the 16 February 2018 issue of Science.
http://science.sciencemag.org/cgi/doi/10.1126/science.aao2117
