Jana Vamosi, Ph.D, postdoctoral associate at the University of Calgary and Tiffany Knight, Ph.D., assistant professor of biology in Arts & Sciences at Washington University in St. Louis, and their collaborators have performed an exhaustive global analysis of more than 1,000 pollination studies which included 166 different plant species and found that, in areas where there is a great deal of plant diversity, plants suffer lower pollination and reproductive success. For some plant species, this reduction in fruit and seed production could push them towards extinction.
One reason that pollen becomes limiting to plants in regions of high diversity may be increased competition between the plants -- there are more plant species vying for the services of pollinators. Also, when there are a lot of species around, plants become more separated from other individuals of the same species, causing pollinators to have to fly long distances to deliver pollen. When pollinators do arrive, they may deliver lots of unusable pollen from other plant species.
Knight and her colleagues found this pattern to be especially true for species that rely heavily on pollinators for reproduction -- those that require outcrossing -- and for trees, in relation to herbs or shrubs, because individuals of the same species tend to be separated large distances when species diversity is high.
To test for pollen limitation of each plant species, scientists added pollen to a number of plants and compared them with control plants that were pollinated naturally. Vamosi, Knight and their colleagues created a database of more than 1,000 pollination experiments conducted worldwide.