Are high-arctic plant-pollinator networks unraveling in a warming climate?

Submitted by editor on 22 May 2018.Get the paper!

Flung into the high North is the Zackenberg Research Station (see our recent photo story in Biosphere magazine). We may think of the Arctic as a barren place supporting few species, but previous work at Zackenberg has shown that many plants, arthropods, mammals, and birds call the North home. Here, as everywhere else, the persistence of each species and the functioning of the ecosystem depend on interactions between species (Schmidt et al. 2017). One critical interaction is pollination: a very large fraction of arctic plants are insect-pollinated (see Kevan 1972) and so must interact in order to reproduce.

Zackenberg research station, Greenland.

Given the importance of plant-pollinator interactions for the survival of insects and reproduction of plants, we were interested in how these interactions changed over time. We generally expect that species interact with the same partners within and across years, but there are many reasons why a new interaction might begin or an old one cease. Interactions can change because species arrive at or leave the site, because one species becomes rare and interacts with fewer partners, because the timings of flowering or insect activity change, etc. The possibility for changes in species’ active periods is especially interesting in the context of climate change.  Plants and insects may respond to different cues (e.g., day length vs. snowmelt) to determine when the plants flower and the insects emerge. If these cues respond to climate change in different ways, species may get “out of step” with their interaction partners. This could be a serious problem if, for example, insects emerge before any plants flower and provide nectar resources.

A selection of the diverse flowering plants and insect pollinators found at Zackenberg.

To see how the interactions between species changed between years and decades, we drew on a classical study conducted by Heidi Elberling and Jens Mogens Olesen in 1996 and 1997 and then repeated by Claus Rasmussen in 2010 and 2011. In each of these years, the researchers heroically spent 8 hours of every sunny day staring at flowers – 20 minutes for each little plant individual. Now try that at the height of mosquito season, armed with a rifle for the event of passing polar bears, and you will know why arctic pollination biology is one of the less popular fields of research.

Claus Rasmussen heroically observing a flower with no polar bears in sight.

Once our heroes had brought home the data, we looked at the pattern of direct and indirect interactions for each species in each year (its “role”) to test whether the roles of plants and pollinators changed over time. We found that they did, and that the amount of change in roles generally increased with the amount of change in the species present at Zackenberg. Our results show that new species arriving at Zackenberg do not tend to replace missing species, resulting in different patterns of direct (i.e., pollination) and indirect (e.g., competition, facilitation) interactions for their interaction partners. As these interactions affect species population sizes and their ability to reproduce, it is important to understand how changes in community composition lead to changes in interactions between species. This is especially true in the Arctic, where ongoing climate change is likely to affect species sooner and more severely than in other areas.

By Alyssa Cirtwill, Claus Rasmussen and Tomas Roslin