Although I (and all the bee biologists I know) am fascinated with the vast and surprising diversity of bees, pollination is often the main reason most people care about these invertebrates. We need them for our crops, in both agricultural fields and home gardens, yet they are also important for maintaining the fields of wildflowers that grace natural habitats throughout the world. Yet little is known about the differences in the efficacy of pollination in these three different environments. Misha Leong, a fellow graduate student here in UC Berkeley’s Department of Environmental Science, Policy and Management, has been assessing visitation and seed set in urban, agricultural and natural areas in California’s Bay Area. Leong used yellow starthistle, a common grassland weed found in all her environments of interest, as a sort of probe to test rates of pollination.
It turns out that in natural habitats, bees visit the thistle in far fewer numbers, yet those same visits results in higher seed set than in urban and agricultural areas. This may be because there are more plant species for bees to choose from in the non-natural areas. That’s right, you heard me, in late summer, when yellow starthistle blooms, human-made environments actually provide more resources than natural areas that are usually starved for water. Spring is prime-time for California’s dry grasslands, so in late-summer, when the native plants have senesced, bees may be more reliant on starthistle, thus carry more pollen during each visit despite having fewer overall visits. Nature is full of little paradoxes like this.
Now as I mentioned, yellow starthistle is a terrible invasive weed. It is prickly and can take over areas rapidly. I am not very encouraged that it might do better in natural areas, the places we most need to conserve. This research doesn’t really point to what we can do to prevent its spread. And it’s harder still to imagine taking away resources from bees at the end of their flight season. Nevertheless, it is interesting that a plant can have high rates of visitation in such non-natural environments as those studied. Hopefully the same proves true for wildflowers or crops we add to our urban and suburban gardens.
This is an open access article, which means you can read the real thing by clicking this link:
Leong M, Kremen C, Roderick GK (2014) Pollinator Interactions with Yellow Starthistle (Centaurea solstitialis) across Urban, Agricultural, and Natural Landscapes. PLoS ONE 9(1): e86357. doi:10.1371/journal.pone.0086357