Oh no, Earth has exploded!
Luckily, we have a backup plan: a single space station and enough storage to keep DNA samples of:
- 5 plant species,
- 5 vertebrate species,
- 5 invertibrate species
Purpose of the Question
A thought experiment mainly. To determine what species would be most important to ensure human survival in a small, closed "world in a bottle" sort of situation.
Note that the important part of the question is human survival. This means that just creating a self sustaining ecosystem isn't enough, it has to be populated by organisms which will benefit us, and fulfill as many niches to human civilization as possible.
The Space Station
This is just a thought experiment. How the Space Station works is irrelevant, but to keep the question specific I will include a few details:
The structure is a Stanford Torus - or, a large ring that rotates to generate gravity. It has a livable interior surface area of 10,000 square kilometers - or, slightly larger than Sardinia.
The interior is large enough to generate weather such as rain and wind. Sunlight is directed into the habitat via mirrors.
Colonists inside have the option to generate electricity in any way they choose, as long as it is within the bounds of modern technology.
In terms of abiotic building materials, they have a limited supply of every element, but cannot rely entirely on metal, etc. to build every structure.
How much water is on board, what sort of biome you want the interior to resemble, temperature, etc. is all up to you and can be customized to fit whatever species you decide to bring.
In terms of the soil and ground, there is enough material to cover every 10,000 square kilometers in 100m of ground. What that ground is made of, whether it is shaped like picturesque mountains and valleys or a great archipelago amidst an artificial ocean is all up to you.
The ship will have to be 100% self-sufficient, so we'll need something to keep the soil nutrient rich and generate oxygen, something to break down any woody plants you decide to bring along, and so on.
The Brave Colonists
And, of course, the humans on board will have to eat, build stuff, etc.
As for their culture and creed, it hardly matters: only that they are simple humans as we know them today and need to develop a hardy, well rounded civilization to survive for as long as possible without access to outside resources.
Of course, the human element can affect ecology: there will (hopefully) be plenty of manpower to manage things like animal populations, sowing forests, etc. How effectively they will be able to manage and live off their quaint little 10,000km is entirely dependant on what species they have to leverage.
- Yes, I know it makes no sense that a 10,000 square km Stanford Torus only has room for 15 DNA samples. This isn't important and isn't meant to be a "how would we do this?" question as much as it is to highlight which plants and animals would be the best space companions over exceptionally long, isolated missions.
- The colonists do not know how to genetically modify their plants and animals, at least not from the start of the mission. What they have is what they are stuck with. They can use run-of-the-mill selective breeding, of course.
- in terms of different animal breeds, we'll keep it simple by saying you only get one.
- Microorganisms would complicate things far too much for the scope of the question. So, for some reason, while the spacecraft only has enough space for 15 DNA samples, it does have enough room to keep cultures of whatever microorganisms the colonists and other species may need, including algae. So no, your flock of space sheep aren't all going to die because they have no stomach bacteria. This does open up the ability to use algae alone to keep the air breathable, but do keep in mind you only have max 10,000 square km of 100m deep ocean, and people do need to live somewhere.
Note: this is the first question I'vd asked here in some time. I spent a few hours trying to account for as much as possible while trying not to go too crazy on the length. I hope I did a good job, but I'm no English major.