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Surviving cannibals

  1. Mar 9, 2008 #1
    May I ask a question please?

    What type of creature, large or small, could sustain it's population by feeding only on it's dead plus air water and sun? Living creature, but not plant life.
    I'm researching for my science fiction novel, so this is important to me.

    Thank you.
  2. jcsd
  3. Mar 9, 2008 #2
    If the creatures expend any energy during their life cycle, then in order for there to be an increase in population (where the creatures maintain their size), there must be an external energy source.
    From what you have that requires either air, water, sun or a combination. Which is getting into the plant realm. Maybe some animal with chlorophyll or something in their skin, assuming the animal is small enough and does very little work.

    Or you could go with:
    1. Decreasing population. Until they all die off.
    2. Same population, decreasing animal size. Ultimately leading to their demise.
    3. Same population, same size, change in animals abilities to perform work. Leading to their demise.

    But then you must also assume no loss of energy to decay of the dead into the ground, at all.
  4. Mar 9, 2008 #3
    Thanks for your answer...just what I need.
  5. Mar 10, 2008 #4
    Thank you so far...this is very useful.

    If I go into the story a little more, maybe a few more ideas will come.

    It's not set in the future so present day science will have to apply.

    A scientist decides to invent an energy creation machine, based on the hamster/treadmill principle.
    Trouble is animals like hamsters need food, water and maintenance....which would make the whole thing non viable.
    So his idea is to use a population of Xanimal.
    We see a population of Xanimals living in an enclosed environment.
    Part of this consists of a treadmill....also "free" stuff like air, water, sunlight.
    They are continously attracted to climb the treadmill, either seeking light, food, sex or whatever. Or perhaps fleeing from something below.
    Obviously their body weight is acting on the treadmill.
    Perhaps their entire lifespan is spent climbing the wheel, all the time reproducing, growing up, eating their dead and possibly their own excreta, but getting nowhere.
    Problem is, what is the Xanimal?

    Thank you.
  6. Mar 10, 2008 #5


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    Step back and look at the bigger picture. Look at this as a closed system first.

    All life on Earth turns Earth chemical resources into work. That's great as long as you consider the life as the system and the Earth as the source of fuel. i.e. life is an open-system.

    But if you consider the entire Earth as a single closed-system, you would do better to simply burn the whole thing, extracting all the chemical energy at once.

    Your critterX-on-a-hamster-wheel system - in its initial state - contains only so much chemically useful energy. No amount of metabolising of any animal will increase this. Thus, you will only get so much energy out of it. Again, the most efficient way to make use of this potential energy is to convert it directly. Your best (non-fusion) usage of this energy would be to burn the entire contents of the cage to carbon and use the released energy to power a turbine.

    That being said, as soon as you start the system in motion, you are allowed to add air, water and sunlight. But none of those things are fuel, they only facilitate fuel collection and production.

    You're still stuck with the initial amount of useful chemical storehouse.

    It is this principle that "The Matrix" is built on, and it is this reason why the Matrix has a dumb premise. Why don't the machines simply use the pulp/fuel that they're feeding the humans by converting it directly into usable energy?
  7. Mar 10, 2008 #6
    Thanks Dave....I suppose what I need is a not-closed system, where I introduce food for the Xbeast, also a way to recycle his faeces and his body when he dies....he needs to reproduce as well.....So the problem is to find the most cost efficient Xbeasts and also the best wheel-machine situation to house them.
    Any more ideas?
  8. Mar 10, 2008 #7


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    Overly speculatitivity warning:

    You MIGHT have a population that began as "normal", but has switched to living off the radio-active decay within their own bodies.

    Such a population might live strictly cannibalistically for some time (destined to doom, though). Possibly. Or not.
  9. Mar 10, 2008 #8
    Last edited by a moderator: Apr 23, 2017
  10. Mar 10, 2008 #9


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    I still don't see the point though. Life is an extremely inefficent mechanism if one's goal is to generate power. Using life to generate power is tantamount to a Rube Goldberg device writ large (i.e. a huge, complex device, that, at the end of the day, accomplishes relatively little).

    There are reasons why you might have to do this, but they would be reasons forced upon the inventor - reasons such as not having the mechanical technology to convert resources into power, yet at the same time having an abundance of genetic knowledge.

    This would make the story more plausible by creating a 'playing the hand he's been dealt' plot device.

    John Varley's Titan had "living devices" like this. The "inventor" in the story, had huge wisdom and technology in creating specialized critters, but not much "hard" technology. So, everything in the world, from motion-picture cameras to jet bombers were merely specialized forms of life.
  11. Mar 11, 2008 #10
    I don't know that this is what Flantoons was thinking about, but I can see a little bit of benefit in that life is self-assembling and self-organizing. The same reason there's interest in some sorts of nanotechnology: if the nanoengineer has done the job right the manufacturing process is little more complicated than making 007 a martini.
  12. Mar 11, 2008 #11
    If you are using one of those perpetual motion treadmills...
  13. Mar 11, 2008 #12
    Actually if your x-animals started out life as a plant like creature then changed into an animal like creature they could eat themselves after they have grown up on sunlight and CO2.
  14. Mar 11, 2008 #13
    I would say that cockroaches can do that, WITHOUT sunlight, whilst having their populations stay the same. There was a really good thing on cockraoches on the Science Channel about these bugs, plus other interesting animals.
  15. Mar 11, 2008 #14
    Does this help?
    http://www.naturesodyssey.com/ecospheres-c-15.html" [Broken]
    An ecosphere can last for 8 years. Big deal, my daughter has made it to 16 years under a 3 foot pile of junk in her bedroom.
    Last edited by a moderator: May 3, 2017
  16. Mar 12, 2008 #15
    Tell me about cockroaches: If I have a box of cockroaches, say 100 roaches in a closed box, but some air coming in (also light and water maybe) What happens to them over a long period?
    Will the population size stay the same. What about breeding dying eating defecating etc?
  17. Mar 12, 2008 #16
    I have an idea of how I can encourage the animals to crowd onto the one side of the treadmill.....they move towards the light, perhaps trying to escape. So by shrouding the left half of the wheel in darkness, this creates a continous movement to the right. Also create a wheel with concentric wheels inside for extra layers of traction. I don't like cockroaches, because they're so light weight. What else could I use? Trouble is using larger animals is cruel.
  18. Mar 12, 2008 #17
    Wow, I have no interest in reading your book, and I read everything.
  19. Mar 12, 2008 #18
    I would say go for it, Flantoons, write your novel. It sounds like it might come out pretty pulp sci-fi but some people like that. And may it be the first of many novels you write.
  20. Mar 12, 2008 #19


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    I guess what you've got here is an energy conversion device, a living motor. It converts fuel (food) into work (axial rotation).

    This would be useful if your characters had a pre-existing source of chemical fuel (could be as simple as dirt) but did not have access to an efficient way of turning it into mechanical motion.

    You'll have to start with a fuel (food) that is rich enough in potential chemical energy, otherwise, you might end up with languid earthworms turning you crank at 1rpd or something.

    Let's see, if it were rich you could just burn it, so your story has to have a reason why the characters can more easily convert it some other way. Hm.
    The food isn't combustible?
    Water's too precious a resource to waste in a fire-driven steam-turbine?

    Perhaps the critters are already doing their thing as part of nature when the character comes along? That would yield high cost-benefit ratio since he wouldn't have to expend huge resources modifying or inventing.

    Perhaps harnessing them to walk is actually beneficial to them - a symbiotic relationship?

    Or, going the other way, lose the food, go directly with solar input. Modified plants that convert solar energy into mechanical motion...
    Last edited: Mar 12, 2008
  21. Mar 12, 2008 #20


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    I didn't know one needed to be concerned with cruelty to fictional animals. :uhh: Maybe they like it, you know, like those strange people who enjoy running on treadmills. Sure, they're rare, but they exist.
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