A New Deal for the Arctic
© Tom Arnbom/WWF-Sweden
Lessons from lemmings
Ecosystem disruptions can have cascading effects on species

The climate crisis will lead to environmental changes that are not always easy to foresee. Tom Arnbom discusses the ups and downs of the Scandinavian lemming to illustrate how the fate of a single species can influence that of many others—and to show that we must begin building a more resilient Arctic now if we want to protect ecosystems and the biodiversity they support.

My first encounter with a Scandinavian lemming was 46 years ago, but I remember it as clearly as if it were yesterday. It was 1974, my first visit to the Arctic. It was a good year for lemmings—and by extension, for the snowy owls that preyed on them. I remember seeing 22 breeding snowy owls all at a single glance—a rare sight. They all had stacks of dead lemmings in front of their young chicks.

The Arctic has changed dramatically since then. The climate crisis has entered the arena dramatically and is now the biggest driver for species changes in the Arctic. Sadly, it doesn’t look good for the Scandinavian lemming.

It’s normal for these feisty rodents to experience boom-and-bust cycles: they can be completely absent from the mountains of Norway, Sweden and Finland (Fennoscandia), then found in enormous abundance there three years later. The rustle of their movements can be heard everywhere in the mountain forest, high up on the treeless tundra and even inside your tent. They are always on the move.

The lemming is at the centre of an Arctic food web. Here is one with Frida Arnbom.
© Tom Arnbom/WWF
The little engine of the tundra

The lemmings’ boom-and-bust cycles influence the diets and even the numbers of many other Arctic species. In years when lemmings are abundant, raptors—such as rough-legged buzzards and merlins, including snowy and short-eared owls—breed in large numbers, with large clutches. Other animals switch to lemming-focused diets, including weasels, wolverines, foxes, brown bears and lynx.

When these predators are busy munching on lemmings, other species benefit. For example, waders and ptarmigans are less likely to become prey. As well, lemming droppings fertilise plants that are eaten by reindeer and Arctic hares—so a strong year for lemmings is good for these species too. Essentially, the Scandinavian lemming is like an engine running the tundra in Fennoscandia.

One species that is particularly influenced by the presence of lemmings is the Arctic fox. This species can typically be found all over the Arctic and is generally faring well in most places today. However, the Arctic fox nearly became extinct in Fennoscandia in the late 1990s after being over-hunted for its fur throughout the 19th and early 20th centuries. Amplifying the situation—for reasons that are not understood, but not related to climate change—the lemming cycles completely disappeared for nearly two decades, from 1982 to 2000. By the end of that period, the number of Arctic foxes had dipped to just 30 individuals in Sweden. Thanks to lemmings and conservation measures, their numbers are now back up to about 200.

Arctic foxes began their remarkable comeback in Scandinavia because the lemming cycles started to run again. Several deliberate conservation measures also helped, such as complementary feeding with dog food at fox dens in the worst rodent years and the removal of the red fox—a larger, more aggressive species that has been known to compete with the Arctic fox for food and prey on Arctic fox cubs and adults.

Still, in Sweden, the Arctic fox normally only breeds every third or fourth year—during “lemming years.” When there are no lemmings, no fox pups are born, while during a lemming year, a female Arctic fox can give birth to up to 18 pups. Fox parents can be a bit stressed about finding enough food for all their hungry, growing youngsters during these years.

Unfortunately, the relationship between the Arctic fox and Scandinavian lemming is starting to break up again due to the climate crisis.

Warmer winters upset ecosystems

Winter temperatures in northern Sweden have increased by an average of 3°C since 1960. Winter rains can now occur any time between October and April, with lethal consequences for lemmings: when the rain freezes, an ice shield is created under the snow that prevents them from reaching moss to feed on. The population can crash, setting off a cycle that affects many other species.

Winter temperatures in northern Sweden have increased by an average of 3°C since 1960. Winter rains can now occur any time between October and April, with lethal consequences for lemmings: when the rain freezes, an ice shield is created under the snow that prevents them from reaching moss to feed on. The population can crash, setting off a cycle that affects many other species.

©Staffan Widstrand, Arctic fox
For example, predators that feed on lemmings do not breed—and they switch to eating other species, such as waders, ptarmigans and hares. When ptarmigans are badly hit by many predators, this in turn affects gyrfalcons, which normally feed on ptarmigans. Sweden has experienced a 30 per cent decrease in the number of breeding gyrfalcons over the last 10 years.

For example, predators that feed on lemmings do not breed—and they switch to eating other species, such as waders, ptarmigans and hares. When ptarmigans are badly hit by many predators, this in turn affects gyrfalcons, which normally feed on ptarmigans. Sweden has experienced a 30 per cent decrease in the number of breeding gyrfalcons over the last 10 years.

©Jan Frode Haugseth, Wikipedia, Rock ptarmigan
This is just one example of how the climate crisis can affect an intricate ecosystem. There are many other Arctic examples. Orcas (killer whales) are one: they are taking over as the top predator in several areas, replacing polar bears when the sea ice disappears. Orcas scare belugas and narwhals away from Indigenous hunting areas, affecting subsistence lifestyles. Another example is in Russia, where greater volumes of freshwater runoff from rivers may change the distribution and behaviour of fish and marine mammals, affecting local people’s ability to hunt.

This is just one example of how the climate crisis can affect an intricate ecosystem. There are many other Arctic examples. Orcas (killer whales) are one: they are taking over as the top predator in several areas, replacing polar bears when the sea ice disappears. Orcas scare belugas and narwhals away from Indigenous hunting areas, affecting subsistence lifestyles. Another example is in Russia, where greater volumes of freshwater runoff from rivers may change the distribution and behaviour of fish and marine mammals, affecting local people’s ability to hunt.

©Staffan Widstrand, Arctic hare

Quick changes in species distribution will challenge many Arctic ecosystems as new predator and prey species establish themselves. With increasing shipping in the region, the risk of new invasive species is also high.

We must prepare for dramatic changes in the Arctic. We can expect to see many new interactions and distributions of species. Some species currently classified as invasive might actually become sustainable food resources for local communities and commercial fisheries.

We can steward the future to a certain degree, but we must be aware that many changes will happen in a way that we do not expect and cannot foresee. We must start the process of building a resilient Arctic now in order to cope successfully with future changes and challenges.

© Bert-Ove Lindström

TOM ARNBOM is a senior advisor on Arctic and ocean issues at WWF–Sweden. He has more than 45 years’ experience in Arctic issues. His main interests are future management of the Arctic and how Arctic species will adapt to climate change. Here he is with a snowy owl.