Honeybees and native pollinators during SoCal summers

When we started designing and collecting data for a couple of field-based projects in the sweltering southern California heat, I became concerned about one of the main challenges in studying pollination ecology during the summers here: there aren’t a ton of flowers in bloom this time of year. (And by “not a ton,” I mean thirty-something species – which sounds like a lot, but most of them are tiny yellow specks floating few and far between in a sea of flowerless shrubs.)

But one plant that abounds at the Bernard Field Station, California buckwheat, is now at the height of its flowering season. It often grows in massive heaps of tens of thousands of little flowers and buzzes with bees (and other pollinators) on sunny days. So we have a great opportunity to study pollinators’ relationships with a plant that will be dominating the botanic landscape throughout the summer until it goes into senescence.

Buckwheat world

There are many reasons why studying pollinator interactions over the course of a plant’s flowering season is of interest. Differences between various pollinators’ foraging habits can provide insight about how and why they have adapted to environmental changes like a major flower resource going into senescence. For example, honeybees are one of the few eusocial insects at the BFS, and their foraging strategies differ greatly from solitary bees since they work collectively as a colony. They’re also not native to this part of the world, but to Asian tropics, where summertime offered many more flowers than they’re getting here, which raises questions about how an organism that evolved under very different environmental conditions can survive under the constraints of a new ecosystem. And thinking about those questions may be especially useful as we see rapid environmental change causing all kinds of ecosystemic shifts and disruptions, from increasingly earlier flowering seasons to road-fragmented habitats to the conversion of wild land for development or agriculture. How do organisms with a certain set of evolved behaviors respond to a changing (or already changed) world?

To compare the foraging strategies of different pollinators at the BFS, we’ll be studying pollinator visitation rates at selected patches of buckwheat. Our study will run throughout the flowering season of the buckwheat, so we’ll get a sense of how visitation changes as flowers are budding, blooming, and senescing – that is, what happens when the resource quality declines. I’m particularly interested in how honeybees compare to native bees and other mostly solitary pollinators. There is some experimental evidence that honeybees forage more persistently than bumblebees at resources with declining value because living in a larger colony enables them to dispatch more foragers, even to less rewarding resources. While solitary pollinators or small colonies have to concentrate their foraging efforts on the best resources with guaranteed payoffs, large honeybee colonies can benefit from allowing some individuals to forage at a less rewarding resource in case it improves again. Based on this argument, we would expect that honeybees will continue to forage for longer than other (solitary or small-colony) pollinators as the buckwheat becomes a less rewarding resource over time. Just how unrewarding will the buckwheat have to be before pollinators decide to move on to the little flowers scattered sparsely across the field station?

A honeybee foraging on California buckwheat

It will be interesting to see how honeybees manage to survive in this landscape, considering that most of the native pollinators time their flight/foraging seasons with the phenologies of native plants. Honeybees, however, are active all summer long. Beekeepers in Southern California struggle to deal with attrition during the summertime, suggesting that their regionally uncoordinated foraging season confers a pretty significant disadvantage. Comparing their foraging habits to those of other pollinators could also help us learn about whether and how they may overcome that disadvantage.

So here’s what we’re doing: every morning or so, Clayton and I go around to three pairs of buckwheat patches (each pair consists of a large and small patch) and count pollinators for ten minute observation periods at each patch. We also measure the number of open flowers, inflorescences, and percentage of senescence at each patch. Other variables that we’re recording are area (size) of each patch, surrounding plant community, and proximity to a honeybee hive (based on the ones we know of so far, our patches are all relatively equidistant from the nearest hive).

Using a quadrat to estimate proportion of inflorescences blooming

Thus far, we’ve been seeing anywhere from five to thirty pollinators during one observation period. We’ve seen a lot of cabbage butterflies, honeybees, and bumblebees. Check back in a few weeks to see what we learn!

Further reading

Al Toufailia, Hasan, Christoph Grüter, and Francis L.W. Ratnieks. “Persistence to Unrewarding Feeding Locations by Honeybee Foragers (Apis Mellifera): The Effects of Experience, Resource Profitability and Season.” Ethology 119, no. 12 (December 1, 2013): 1096–1106. http://onlinelibrary.wiley.com/doi/10.1111/eth.12170/abstract

Rivera, Michael D., Matina Donaldson-Matasci, and Anna Dornhaus. “Quitting Time: When Do Honey Bee Foragers Decide to Stop Foraging on Natural Resources?” Frontiers in Ecology and Evolution 3 (May 19, 2015): 50. http://dx.doi.org/10.3389/fevo.2015.00050

Townsend-Mehler, John M., and Fred C. Dyer. “An Integrated Look at Decision-Making in Bees as They Abandon a Depleted Food Source.” Behavioral Ecology and Sociobiology 66, no. 2 (November 1, 2011): 275–86. http://link.springer.com/article/10.1007%2Fs00265-011-1275-2