Norway has not seen the mass suicide of lemmings for 15 years, which was previously repeated every three years. It turns out that climate change is to blame for this too - constant thaws turn Norwegian snow into an insurmountable obstacle on the way of lemmings to the stern. The absence of "suicide" is not a blessing, but a symptom of the unhealthy Norwegian ecosystem
The instinct of self-preservation is inherent to one degree or another in all living beings. But it seems that in lemmings - modest rodents from northern Europe - he sometimes completely refuses. Lemmings have been noticed more than once in massive numbers drowning in local water bodies, where they go, at first glance, completely voluntarily. Probably, this behavior of the animals inspired the creators of the now legendary computer game "Lemmings". In it, the player was asked to bring a horde of several dozen creatures to the final destination, recklessly rushing into deadly traps placed along the way.
In fact, "suicide" is a myth, and we owe its appearance to a curious combination of environmental factors that provoke the peculiar behavior of rodents.
The fact is that in snowy Norway, where lemmings are most numerous, these animals have occupied a very special ecological niche. Snow in Norway lasts most of the year, and the temperature regime is such that the bottom layer of snow adjacent to the ground always melts a little. A thin layer forms here, which lemmings use for their winter travels in search of food - mosses and lichens. Most of the winter lemmings can feel completely at ease - a thick layer of snow reliably protects them from the cold and from polar predators.
Female lemmings are capable of producing offspring up to three times a year, each time giving birth to up to twelve new rodents. It so happens that such fertility leads to an incredible rise in the population of lemmings. Many Norwegians remember how, in the freezing winters of the 1970s, snowblowers, along with snow, removed the numb carcasses of crushed rodents from the roads.
For the animals themselves, however, the consequences of such a demographic boom are always sad. Gluttonous lemmings quickly devastate all stocks of even the slightest edible mosses and lichens, after which a massive migration begins in search of new food sources. It is in such years that people observe "mass suicides".
In migration, huge flocks of rodents inevitably stumble on their way into water bodies, in which they drown in whole packs. But not at all from despair and not in the hope of finding some kind of food there. It's just that those who walk in front are literally pressured by those who are walking behind, and the "vanguard" is unable to turn back. Small streams and ponds for lemmings are not a hindrance - they swim very well, but sometimes during a hysterical mass migration, rodents get to the Norwegian fjords, where, pushed by the crowd, they recklessly and en masse rush into the cold ocean waters. There they find their end.
Such demographic explosions, accompanied by a further no less dramatic extinction of lemmings in the past, had a periodicity and occurred on average once every three to four years.
However, for 15 years the population of cities and villages in Norway has been living without rodent infestations
It's not that Norwegians miss the old days - lemmings are often compared to a locust infestation, but the reasons for the failure of a natural mechanism that worked like a clock throughout Norwegian history and, apparently, millennia in prehistoric times, raise questions.
The biologist Niels Stensen from the University of Oslo managed to answer them, having published an article with colleagues in the latest issue of Nature.
According to scientists, lemmings have ceased to die of hunger and drown in rivers and lakes due to global warming.
This conclusion allowed the scientist to make a comparison of the dynamics of many factors influencing in the northern country.
Stensen was helped by the meticulously documented weather parameters over the past few decades. He analyzed the trends in moisture changes, the thickness of the snow cover, the hardness of the lower layer of snow directly adjacent to the ground (and this characteristic is recorded by Norwegian meteorologists), as well as the dynamics of lemming populations, estimates of which he made from records of rodent capture. There was a clear connection between the former and the latter.
The scientist was able to build a mathematical model linking the dynamics of populations with the relative humidity of the air, the amount of snowfall and the duration of the snow season.
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Stensen concluded that the end of the population explosion in lemmings was due to changes in the lower layer of snow.
Lemmings'
suicide The scarcity of tundra vegetation limits the number of lemmings, but once every 3-4 years, when food is abundant, their population flares up. The Arctic tundra is unable to feed so many …
From frequent thaws and increasing humidity, thawing and then re-freezing snow turns into a dense and stubborn crust of ice. It not only blocks lemmings from sub-snow passages to feeding places, but often makes pasture completely inaccessible. This inevitably and adversely affects the ability of females to nurse large broods of young lemmings. Additional difficulties are brought by the flooding of the lowlands - the lemmings trapped in them are doomed - as well as the shortening of the snow season, which gives predators access to rodents earlier than before.
Stensen's mathematical model was able to very accurately describe the occurrence of the population explosion in the population of lemmings in the past until the last boom in 1994.
And she also shows that since then there could be no new explosions of the rodent population
Stensen's work may seem controversial, as it is based on pure comparison of graphs and diagrams. However, any skeptic should remember that people started talking about global warming even before Kilimanjaro lost its snow cap, the Greenland ice sheet began to rapidly melt and the ice cover of the Arctic dropped sharply. The first ideas about the onset of global warming of the planet's climate were obtained using a very similar analogous comparison of graphs. And in general, in climatology, scientists often only have to rely on long-term records of weather stations.
The value of this work also lies in demonstrating the delicate balance between weather factors and the life of the biosphere
Today, a small shift in average annual temperature in Norwegian latitudes has led to a decline in lemmings, and tomorrow it could lead to a decrease in the number of polar foxes, owls and wolves that feed on rodents. The way Stensen has learned to assess the dynamics of wildlife populations not only demonstrates the power of mathematical analysis of long-term data, but is likely to help prepare for the new challenges of the changing climate of the Earth.