How would life adapt to survive in an environment with winters of varying length?

Question

In his answer to a question on our Science Fiction and Fantasy SE about how Westeros in Game of Thrones produces food during the winters, Superbest says:

"Martin's conception of a multi-annual winter is a little bizarre in my opinion. If this has been going on a geological time scale (eg. millions of years) it would either create flora and fauna radically different from what we see here on Earth, while the novels seem to portray basically the same animals and plants we have, with the occasional exotic exception".

So, how would an animal evolve to survive on a planet where winters and summers lasted varying, random lengths like in Game of Thrones? What common traits would develop among animals in general? (I know there would be wild differences based on predator/prey status and such, but there would also be similarities - what would they be?)

Assumptions:

Winters can last anywhere between 1 and 30 years at a time. 99% of the time it will be somewhere between the 2 and 10 mark, however.

Summers work the same way, with summer instantly kicking in after winter ends. The length of a summer has no relation on and in no way impacts the length of a winter and vice versa - it is totally random within the above parameters.

We will also assume that this world has obviously been like this for long enough for animals to evolve, if not from its beginning.

Edit 1:

The sun remains in "summer mode" for the duration of summer, and "winter mode" for the duration of winter in regards to the length of the day. It is also, obviously going to be horrendously cold for the duration of winter in the northern hemisphere.

Outside of this, the world is exactly like Earth.

Answer 1

I have always thought of the Westeros cycle as more like climate change than like seasons. Specifically, there are seasons, just like in Europe or North America, and superimposed over the annual cycle of seasons there are climate oscillations induced by some kind of oceanic phenomenon, somewhat similar to the El Niño / La Niña phenomena on Earth. The transition from a warm period to a cold period may be very short or it may last a few years -- my impression from the books and from the TV series is that when winter comes the years get progressively colder, but then I may be wrong.

It may be that such a world will give preference to hardy animal and plant species which can survive both cold and warm times. It may also be that some areas are always cold and some are always warm -- for example, the area beyond the wall seems to be always cold and the areas inhabited by those barbarian nomads and amoral slavers seem to be always warm; the areas in between would then be colonised by cold-loving species in cold times and by warmth-loving species in warm times. Probably a mix of both.

The main threat posed by cold spells in Westeros (forgetting about undead foes) is that agricultural output collapses, as expected. The long winters are times of hunger.

Think of how many animal and plant species can be found everywhere from the Artic Circle to the tropics: fir trees, and deer, and wolves, and grasses, and birds. They may dominate the north and be restricted to higher altitudes in the south; they may thrive in more temperate areas and be restricted to favorable locales in the north; but definitely there are plants and animals which are (or would have been in the absence of humans) common to all Europe, from cold Norway to warm Italy or Greece.

Answer 2

Unpredictable winters mean you need to be ready for them at any given time. I guess plants would have weak fast growing branches with thin leaves or something. They're easy to grow and not a huge loss if frost suddenly kicks in.

Then when it's cold you hibernate. Same goes for animals though I don't think a single complex organism exists that can hibernate for years. Tardigrades totally can but they're not that complex. They build wouldn't work for a more advanced creature like a primate.

I actually think the whole setting would exclude the evolution of advanced fauna. Flora will be things like trees that can survive outside combined with plants that use an extensive root system to survive the cold. This can't support large animals as there would be little nutrients above ground.

Smaller animals could probably survive if they produce very 'expensive' eggs that can hibernate through winter. Probably buried underground. Animals living short lives while they pour all their energy into hibernating eggs who would emerge at first spring.

Of course there is one exception, the ocean. The water would largely nullify the effects of the winters. Underwater you'd have a teaming ecosystem.

Answer 3

Flora

Trees - Pine trees and other coniferous trees are actually already decently suited to this setup. Their seeding usually depends on fire and not a normal spring thaw seed that many other plants use, which means prolonged winters are not a threat to their reproduction. We already see much of this in the north. That said, these trees need the root structure and therefore can't survive in tundra/marsh and will be more common in mountainous terrain. Trees that loose their leaves wouldn't fare well in this setup.

Bush/shrub. Take from the current tundra, there are some hardy plants out there. Moss and the sort also tend to do quite well out here. I believe you will see some berry plants (wild blueberry) capable of surviving the elongated winters as well, some adaptations to the seeds to stay dormant until the summer phase appears will likely allow for berries to exist in these setups. I don't think 'raspberries' and other semi-permanent bushes would do well.

In both the cases above, it's likely these plants will support very expanded root systems for storing reserves through the elongated freezes.

Animal life

I believe hibernation is out as a survival technique...the lack of definite summers pretty much rules out the store up fat and sleep option simply because the animal has no ability to guess how long it would be asleep for and how many reserves it would need to build up.

Life on land under ice - Ice is actually an excellent insulator and even in extreme cold, under the ice can still be inhabitable. Given the prediction of the expanded root systems, there should be additional nutrition to be found under the ice. Lemmings and other rodents could survive under the ice along the southern areas of this winterland.

Life on the land, herbavores. Migration has always been a valid technique for animals. That being said, it's 'seasonal' migration based on a constant cycle...if the season instant predictable, then these animals are going to need to adapt and find food locations during the extended winters, while still having a trigger to go back north. If there are larger herbivores wandering around the region, they will likely be migratory.

Life on the land, predators. I believe wolves living on the southern areas hunting both migratory and creatures under the ice should be able to adapt to these situations.

Life on sea ice. Honestly, I don't think theres much of a change in behavior here. If you have frozen over sea water, life on and off the surface will not have the cyclical nature it currently does, but I suspect the life (seals/fish/whales/bears) would not be greatly effected.

Side note:

I live near the rocky mountains and am very familiar with the spring melt off. Winter snow packs up during the winter and when the warmer temperatures come, the water melts and the rivers greatly increase in volume and speed. With some rains added, we've seen some vicious flooding over the last decade. I would imagine a prolonged 30 year winter cycle jumping straight into a summer cycle would create some outright vicious flooding as the snow pack melts...rivers seeing 50x volume and low laying areas becoming completely waterlogged.

Answer 4

Maybe I've got a different conception of what the seasonal changes were in Westeros--but from reading the books, it seemed that they still had the yearly 4 seasons, it's just that the temperature and rain fall would be higher or lower for a number of years, based on whether it was in years of Summer or Winter.

So like, in a Winter year, the summer would still come, but it would be shorter, and the temperature would never climb to record highs in a Winter year. It also seemed to depend on where you were--so in the South, it would never be as cold as it is up North.

I thought of it as a large meta seasonal change that they noticed--normally in the South, it doesn't snow (just like say, Atlanta) but every once in a while, we get surprised by a snow--but in Westeros, they know that it's going to colder than it normally would be and there'd be a chance of snow in a very Southerly area--and they know it's going to be during a Winter cycle, most likely Winter/winter, or during winter season in a Winter year, especially if it is forecast to be a harsh one.

It seems to me that the temperature ranges are within acceptable parameters as far as evolution is concerned.

That being said, let me get down to your question:

• knowing when to leave and where to go. Migration can be very helpful.
• mammals have the advantage. but lizards need to be able to hibernate for decades if at all possible.
• plants have got to be tougher and be able to grow and flower more quickly to take advantage of the small windows of optimum temperature and sunshine during a "Winter" year. They also have to be able to re-grow and go dormant if needed.

I honestly don't think life would be all that different, except that animals and plants would be tougher.