Aoife Cantwell-Jones: How Arctic bees interact with plants depends on body size variation and spatiotemporal context

Aoife Cantwell-Jones—a PhD student at Imperial College London, UK—shares with us the background behind her recently accepted paper, “Mapping trait versus species turnover reveals spatiotemporal variation in functional redundancy and network robustness in a plant-pollinator community.” She discusses nuances of bumblebee-plant interactions and the importance of researching mutualistic interactions to solve global change issues, as well as celebrating teamwork.

About the paper

The intricate interdependencies of plants and pollinators underpin some of the most fundamental aspects of the natural world that are critical for human nutrition, health and welfare. It is no wonder, then, that scientists have long looked to untangle the network of threads that link plant-pollinator interactions.

One key approach in recent years has been to incorporate information about the morphological traits of interacting individuals. Based on the premise that traits are important for determining the likelihood of two species interacting, this approach has tended to assign an average (mean) trait value for a given morphological trait per species. This assumes, however, that trait variation within a species is small, relative to the trait variation between species, and that mean trait values remain relatively constant over time and space.

But, is this assumption valid? Just like height differences in humans, trait variation exists within species. In our study we used bumblebees as a case study in order to better understand how variation in body size over space and time could alter our view of plant-pollinator interactions.

A bumblebee foraging on a willow (Salix) catkin (credit: Frauke Caliebe)

We tested the role of intraspecific variation in shaping interactions between plants and bumblebees in a (beautiful!) montane arctic ecosystem in Sweden. Through a lot of hiking and field observations (estimated >550 km), we collected both trait (body size) and interaction data for individual bumblebees over three annual seasons. Then, by incorporating data on intraspecific variation, we saw the limitations of using mean trait values (at least for bumblebees), as body size declined over the course of the season due to a shift from queen- to worker-dominated foraging.

We were also able to disentangle some more nuanced aspects of plant-bumblebee interactions by mapping how an environmental gradient may influence the importance of morphological traits for interactions. When we incorporated intraspecific variation into computer-simulated extinctions, we found that losing groups of morphologically similar bees led to faster co-extinctions of flowering plant species (a loss of interactions) at nearly all points in space and time. The only exceptions were at high elevation, early in the summer season, when losing taxonomically similar individuals was instead worse.

About the research

Our research fits into the broader aim of developing more predictive frameworks for plant-pollinator interactions—a current research priority, given that environmental change is reshaping species interactions globally. Indeed, although we focus on plants and pollinators, the results of this research apply to other types of mutualistic interactions (such as seed-dispersal) or networks (such as food webs), especially the role that intraspecific variation can play in mediating interactions.

Principal investigator, Dr Richard Gill, showing PhD and master’s students, Aoife Cantwell-Jones, Lucia Hudson and Suzi Egleston, how to non-lethally catch bumblebees (credit: Frauke Caliebe)

To this aim, we plan to keep collecting such high-resolution trait and interaction data. Our hope is that it will be able to answer questions about how climate change may be affecting intraspecific variation, and how this could have ripple effects for plant-bumblebee interactions. More specifically, our next steps will be to collect data on other morphological traits (as bee foraging preferences likely result from a complex interplay of traits) and start visualizing species in multidimensional trait space. We are curious to see whether bee species that are similar in trait space also forage or use the landscape similarly.

About the author

Lead author (Aoife Cantwell-Jones) and principal investigator (Dr Richard Gill) at the field site in Arctic Sweden (credit: Frauke Caliebe)

I became interested in bumblebees when I joined a project in the Gill Research Group at Imperial College during my Master’s degree, looking at signatures of stress in UK bumblebee museum specimens. During that project, I was stunned to learn that bumblebees and honeybees are not the same (I know, shocking that I was so unknowledgeable!) and that there are more than 250 species of bumblebees worldwide. Since then, my fascination with bumblebees has only grown. How can they be both so cute and so globally important for food security?

Now, during my PhD, I have the privilege to continue studying bumblebees—only this time in the field. And, no doubt, one of my favourite experiences as an ecologist has been this fieldwork: there is something truly unforgettable about seeing a bee flying over a large snow patch or how it can find a tiny flower that to us is undetectable. Aside from the bees, nothing beats working alongside a team of highly motivated individuals (we call ourselves the “Humla Hunters” after the Swedish word for bumblebees), and I hope to keep having the opportunity to do this in the future.

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