Uncertain future for Arctic ecosystems
Despite the rapid changes taking place in the Arctic climate, there are no signs that pollen transport to mountain avens has declined over recent decades. But the system is vulnerable – much of the pollination is carried out by just a handful of flies, and some of them are declining locally.
In her doctoral thesis, Deanne Redr has studied how insects, plants and microorganisms interact in the Arctic, including how pollination works. Most of the studies were conducted in Greenland, with additional work in Cambridge Bay, Canada.
– We often think of the Arctic as a barren desert where few species survive the bitter cold. But even here, relationships between species form complex networks, says Deanne Redr, doctoral student at the Department of Ecology.
These relationships are now threatened by rapid, human-driven warming. The Arctic is warming four times faster than the global average, making the region an excellent early warning system.
Unpredictability is a problem
Deanne Redr has found signs that flowers and pollinators may be drifting out of sync. At both sites, brief periods occurred when flowers had too few pollinators, especially early in the season. But the bigger problem was the opposite: periods when many insects were active but too few flowers were available.
This is a warning sign, as hungry pollinators may fail to reproduce successfully, while flowers that receive too few visits risk poor seed set.
When the researchers then looked at changes over 25 years, they found another pattern. The number of weeks when plants or insects lacked potential interaction partners increased, while the differences between years also became greater. In other words, the system has not only changed – it has also become more unpredictable.
– Warming itself is not the greatest threat, but rather the large variation from one year to another. As weeks without potential interaction partners become increasingly unpredictable, it is harder for both plants and pollinators to adapt.
Pollination stable over 20 years
Despite these warning signs, there is no evidence that pollination is on the verge of collapse. Estimated pollen transport showed no clear upward or downward trend over the 20-year period studied.
During five field seasons, researchers observed individual flowering plants, including mountain avens and Arctic willow, for 20 minutes at a time and recorded which insects visited the flowers. They then caught the insects to identify them.
– This result is genuinely hopeful, but at the same time it is worrying that pollination is carried out by just a handful of flies, some of which are already declining locally.
The thesis also uses data on how effective different insects are as pollinators. In this experiment, flowers were covered with plastic cups. Once the cups were removed, the researchers waited for an insect to visit, recorded which insect it was and measured how much pollen had been deposited on the flower.
– It was a really cool experiment that gave us a detailed picture of just how much different groups of insects vary in their contribution to pollination.
The future is uncertain
The relationships within an ecosystem can be pictured as a web, with species and their interactions forming the threads. If a species that many others depend on disappears, the effects can ripple through the network. The web becomes thinner – or begins to break.
– It is clear that ecosystems are being affected by warming, but it is difficult to draw firm conclusions about exactly where this will lead. We simply do not know what the future will look like.
What about the microorganisms?
All plants on Earth are associated in some way with fungi, bacteria and other microorganisms. The same is, of course, true in the Arctic.
The thesis shows that the part of the plant colonised by microorganisms was more important for microbiome composition than the plant species itself. Microbial communities were more similar between two roots from different plant species than between a root and a leaf from the same plant.
Another interesting finding was that plant species sharing many of the same pollinators also had more similar floral microbiomes. This was shown in an experiment in which some flowers were covered to prevent insects from visiting them. Pollen is therefore not the only thing insects carry with them – they also ferry tiny hitchhikers from flower to flower.
Thesis
Dissertation
Contact
-
Person
-
PersonAnna Lundmark, Communications officer, SciFestDepartment of Ecology , joint staff/department office