In my story a group of characters will be sent to a space habitat which contains some of the deadliest alien creatures for a survival training mission.

The majority of the species will be carnivores as well as some dangerous herbivores.

To make this question answerable I will make a comparison to earth animals and ask how long a habitat of said animals could sustain itself.

The rotating cylinder will have a 2km diameter and 10km length giving it a surface area of 69km2, full of terrain suitable for each species such as, forests, grass plains, rivers, hilly areas and larger bodies of water.

The earth animals most comparable to the alien creatures are as follows:20 x Wolves, 3 x bears, 20 x hyenas, 15 x lions, 5 x jaguars, 3 x tigers, 2 x anacondas, 10 x komodo dragons, 10 x eagles, 10 x crocodile. herbivores will include 15 x hippos, 15 x rhinos, 5 x gorilla's, 15 x buffalo.

Some of these figures are taken from the average group and territory size and some are just amounts I chose. there will be a sufficient amount of males and females as each species will be used to having in a group, enough to hopefully allow them to breed.

There will be a plentiful amount of vegetation, creatures like bees and hummingbirds will help to pollinate. There will also be fish and small rodents to serve as a source of food for the carnivores, although small and hard to catch. plankton, smaller fish and algae will be in the bodies of water to provide food for the larger fish.

The point of this habitat is purely to be a challenge for the group to survive or complete a task like getting to the opposite side of the cylinder. I wondered with a major lack of suitable prey how all the predators would react or survive?

It is known when some predators share the same space they tend to stay out of each others ways such as wolves with bears or lions with hyenas but there will be cases where the young, weak or old will be attacked.

I am wondering if I should have all creatures released into separate areas as soon as the group arrives, or could they survive in the habitat and make it home given enough time, so that when my group arrive they will have found their suitable areas and learned what other creatures are there and if they should avoid them.

For an extra experiment when the group finishes the training and leave the cylinder, and because my story doesn't have FTL it might be a few thousand years before anyone thinks to even return to the cylinder. If the creatures were able to survive for a short amount of time in the cylinder it would be interesting to see if anything remains or has adapted thousands of years later.

Apologies for the long winded question and if it sounds like I am asking "who would win a fight between x and y?". I could have summed it up as could a habitat of mostly carnivores and hard to kill herbivores sustain its self for a length of time?

Could this habitat theoretically sustain itself for a length of time? would the predators hunt each other sooner than they would in the wild with more space and prey? which type of creature could likely survive the longest if the vegetation, rodents and fish survive and multiply?

If there are any further details needed to make this answerable let me know and I will update the question.

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    $\begingroup$ You need a lot more herbivores than carnivores to make a self-sustainable ecosystem. As in twenty to fifty times more. Look at any documentary about the Sergenti; see the vast herds of gazelles etc. and the tiny number of lions. Otherwise all your carnivores will die of starvation. (And tigers do not catch rodents. They wouldn't even consider a mouse to be in the category "potential prey".) $\endgroup$
    – AlexP
    Feb 28, 2020 at 15:36
  • $\begingroup$ @AlexP I intentionally left out usual prey like many ungulates because I wanted the area to be non stop threats, so the only herbivores I chose were ones know for being as dangerous as the predators. I do have some plans for real sustainable habits, like child friendly safaris but this one is basically a monster zone. $\endgroup$
    – user69935
    Feb 28, 2020 at 15:42
  • $\begingroup$ The idea for the rodents were to allow those predators that could catch them (like wolves) to survive, then the larger prey would only have to choice to kill hippos etc or kill the other predators, leading to some interesting dynamics and new hunting techniques, but as everyone has pointed out they likely wont survive due to lack of space and suitable prey. $\endgroup$
    – user69935
    Feb 28, 2020 at 16:47
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    $\begingroup$ This sounds more like a video of Totally Realistic Battle simulator. I must admit I would watch. $\endgroup$
    – Willk
    Feb 28, 2020 at 23:24
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    $\begingroup$ @RandySavage - that sounds fun. I like to think the virtual battling animals are also having fun in Ark Survival Animal Valhalla. I will check it out. $\endgroup$
    – Willk
    Feb 28, 2020 at 23:47

4 Answers 4


Just Taking it as it Comes.
Thus far you've gotten lots of excellent answers dealing with why this isn't likely or sustainable, so I'll take a different approach. Clearly, we're dealing with a heaping helping of narrative necessity: you need this ecosystem to exist & function for your story. All well and good. You're also curious about future fortunes. Also well and good! So let's just look at the numbers and see what might still be around after the structure is abandoned and forgotten about.

Short Term:
You say this is intended to be a kind of monster fun zone constructed for training purposes. Kind of like throwing an orienteering class of Boy Scouts into the Arena during one of Caligula's Happy Fun Time Safari Games.

I think for the relatively short term duration of the training session, your ecosystem will be fine. Training session probably won't last more than a month or two, so even your big cats should be okay. Especially with the injection of fresh meat in the form of raw recruits!

Long Term:
Over the long haul, I think you'll see a drop-off of the bigger carnivores with a gradual increase in the smaller carnivores and herbivores.

You mention the existence of fish and rodents. You don't specify, but that could include anything from voles to capybaras and kangaroos. (Basically whopping big jumping rats.)

These are your numbers, for review, and what I think might happen:

  • 20 x wolves -- wolves are opportunistic and will scavenge if hunting doesn't pan out: they'll be okay
  • 3 x bears -- bears are omnivores and are happy either hunting, fishing or scavenging: they'll be okay if three are enough to form a healthy population going forward
  • 20 x hyenas -- hyenas are adept hunters and scavengers: they'll be fine
  • 15 x lions -- lions hunt and scavenge as well so will be fine in the short term; lion habitat seems to lean towards savanna and open woodland so you may have too many lions for the relatively small amount of open grassland: these will probably be the first to fail
  • 5 x jaguars -- it is possible that jaguars scavenge; but worse is that their habitat calls for lowland swampy woodlands: these may not fare so well either and will probably not last very long
  • 3 x tigers -- tigers scavenge as well as hunt and like a wide variety of habitats: they should last a while
  • 2 x anacondas -- anacondas are tropical animals and like rainforests and rivers; they eat just about anything including small crocs, fish and rodents: they'll be fine
  • 10 x komodo dragons -- komodos hunt and scavenge but they really like extremely warm temperatures: they will probably fail to thrive in your environment
  • 10 x eagles -- eagles are fishers & scavengers: they'll be fine
  • 10 x crocodile -- crocs eat just about any animal that gets near its mouth: they should be okay
  • 15 x hippos -- hippos are big and pretty badass; lions & hyenas & crocs might try to take down a baby, but they risk much in doing so and you've only got 15 lions to play with!: they'll be fine wallowing in the wetlands
  • 15 x rhinos -- rhinos are big and pretty badass too; again, your big cats might try to take down a baby but at considerable risk: they'll be okay
  • 5 x gorillas -- gorillas eat plants and insects, especially termites and ants and are not usually preyed upon: they should be okay in the woodlands
  • 15 x buffaloes -- big prey for big carnivores; in the short term, they should be okay, however, these are just the tasty treat your lions, tigers, hyenas and maybe even wolves will be hankering for! There's only 15 of them vs about 60 big predators. I think these will fare worst of all the prey animals: they may not even survive the short term!

All in all, I think you'll have some kind of recogniseable ecosystem in the long term. It may be lacking a couple key predatory & prey animals, though. You don't specifically mention other classes of animals apart from fish and "rodents" and you don't mention other kinds of birds or insects at all. I think your small predators (wolves and hyenas) and your large herbivores (hippos and rhinos) will do best; and I think your scavengers and omnivores (bears) will also be fine in the long run.

Any animal who has peculiar habitat requirements (komodos) will likely suffer.

A thousand years is a long while: though I doubt you'll notice any particular leaps in evolution, you may find some "island effect" taking hold: a decrease in size of large animals, etc. Wouldn't that be cute to come back in 10,000 years and find chihuahua sized wolves and backpackable rhinos!?

  • $\begingroup$ Great answer. thanks! I'm quite happy that most of my favourite ones survive and great point about the "island effect" that is a cute image. $\endgroup$
    – user69935
    Feb 29, 2020 at 19:12

I have the gut feeling that it's too small for all the animals you have put in.

Just to look at one case: you have put 3 tigers in 69 square kilometers

What is the territory they need?

A tigress may have a territory of 20 km2 (7.7 sq mi), while the territories of males are much larger, covering 60 to 100 km2 (23 to 39 sq mi).

If you have 3 tigresses it might be enough, but of course they won't be able to reproduce.

But that only if the entire territory was suitable for tigers to live in. If that's true, it's not a territory suitable for rhinos, hyenas and I suspect also lions, just to name few out of your list. Incidentally, rhinos, hyenas and lions also do not share environment with anaconda, nor with bears.

Most likely part of those animals would starve, and the resulting threat would then be greatly reduced. Normally apex predators tend to stay away from men.

  • $\begingroup$ I chose 3 tigers just to make the numbers seem fairer, I knew they would be forced into a smaller territory that they are used to, with the animals from different habitats I would tailor the cylinder to meet their need, with one area lit up more and hotter for the African creatures, or my alien versions. I did think they would starve as you suggested, maybe the quick release method for the challenge would be better then. $\endgroup$
    – user69935
    Feb 28, 2020 at 14:47
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    $\begingroup$ Lions and Tigers and Bears, oh my! $\endgroup$
    – Thucydides
    Feb 28, 2020 at 14:54

As noted, predators need large amounts of territory, not just becasue they will fight each other, but also as a function of how the ecological pyramid actually works. Plants have generally low conversion efficiency from changing sunlight into carbohydrates and sugars (as low as 1% - apparently the theoretical maximum is about 6% before you run into heat rejection effects).

The conversion of plans into energy and meat on the hoof by herbivores is equally low, and then the conversion of meat into energy by the predators is also equally low.

enter image description here

Energy pyramid

So you would either need to have an actual Island 3 structure (8.0 km in diameter and 32 km long) or even larger constructs like a "Bishop Ring" (which has the surface area of a continent). The huge structure will have sufficient area to support large populations of plant life, which can then support large populations of predatory animals as well. The downside, of course, is that the hunters will need to cover large areas in order to find either meat animals to hunt on their own, or predators to encounter for their "test".

enter image description here

"Yeah, there is a pride of Lions near the other end cap...."

The challenge can be upgraded by ensuring that the habitats are also stocked with the appropriate aggressive herbivores or omnivores as well. Wild boars, herds of Bison or Cape Buffalo or even Hippos are pretty territorial and aggressive, and indeed during the Bronze Age one of the tests of manhood was hunting dangerous animals like lions, wild boar and Aurochs (wild cows). Lions and Aurochs were hunted to extinction in Europe during this time period.

So ultimately you will need to have a habitat of sufficient size in order to support a large enough ecology to support a population of predatory animals. The habitat and ecology should also be coherent in order for the ecology to "work" properly (randomly throwing in creatures will have several acting as "invasive species" with no natural checks and balances, which will destabilize the rest of the ecology in a closed system). If you are far enough in the future, then by al means a Bishop Ring is by far the best choice to ensure this can be done.

enter image description here

"Is there a bear in the woods? I'll have to check..."

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    $\begingroup$ Thanks gives me more to think about, I designed the cylinder small because its almost a throw away project, I would rather save the resources to build larger ones for my civilizations to live in, i almost don't care about the life in the nature cylinder, as harsh as that sounds lol. i may ramp up the size like you say and house way more life. $\endgroup$
    – user69935
    Feb 28, 2020 at 15:25

I note that a cylindrical space habitat can be designed with many concentric cylindrical levels of surface area, separated by countless cables from above and/or pillars from below, so long as the difference in apparent gravity between the innermost and outermost cylindrical level is not too great to affect the health of specimens living there. There can be a number of ramps leading from one level to the next, so that herbivores and carnivores can move between levels.

A space habitat with ten levels could have the same total surface area as a single level one that had 3.1622 times its dimensions; a space habitat with one hundred levels could have the same total surface area as a single level one that had 10 times its dimensions;a space habitat with one thousand levels could have the same total surface area as a single level one that had 31.622 times its dimensions; A space habitat with ten thousand levels could have the same total surface area as a single level one that had 100 times its dimensions; and so on.

There are islands which have herbivores large enough that the predators on those islands are dangerous apex predators which can kill and eat humans. The smallest such island in surface area would seem to indicate the lower limit for a habitat with predators capable of preying humans.

Islands that that support populations of elephants, or which once supported populations of extinct proboscideans that did not shirk in body size due to island dwarfing, would be able to support populations of even the largest mammal herbivores. Similarly, islands that support or once supported populations of hippos, rhinos, cape buffalo, bison, etc. would be large enough to support the largest herbivores, and thus presumably would be large enough to support populations of the largest predators.

And you could find out the sizes of islands that support large predators.

For example, Tasmania has an area of 64,519 km2 (24,911 sq mi). Tasmania is the home of the Tasmanian devil, and was the home of the extinct Tasmanian wolf or Tasmanian tiger, Thylacinus cynocephalus, which might have been capable of preying on humans.

Tigers, Panthera tigris, have lived on large islands like Java (138,793.6 square kilometers or 53,588.5 square miles) and Sumatra (473,481 square kilometers or 182,812 square miles), but have also lived on much smaller islands like Bali (9,780 square kilometers or 2,230 square miles). And tigers sometimes attack humans.

The Komodo dragon[4] (Varanus komodoensis), also known as the Komodo monitor, is a species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, and Gili Motang


Komodo has an area of 390 square kilometers or 150 square miles, Rinca has an area of 198 square kilometers or 76 square miles, Flores has an area of 13,540 square kilometers or 5,230 square miles, and Gili Motang has an area of 30 square kilometers or 12 square miles. Komodo dragons became extinct on the smaller island of Padar about 1975.

Komodo dragons sometimes attack humans:


These examples may help you decided how many square miles of of surface area are needed for your predators.


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