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Let's say there is a sapient species around the size of an t-rex, they weigh on average 6000-8000 kg and are omnivores whose diet is mostly composed of plant matter, but with some meat. They are around as advanced as late neolithic or early bronze age humans.

Would a village populated by 100 of the creatures be sustainable in the long run? Are there any ideas for agricultural methods efficient enough to meet their energy needs to settle permanently in an area or would they have to be nomadic in order to prevent overtaxing the environment?

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    $\begingroup$ Wouldn't that be the equivalent of a town of ~13000 people? Or perhaps less since larger creatures tend to have slower metabolisms? Even 1000 people is too much for a single nomadic tribe, methinks. Or maybe not, I don't know anything about nomadic tribes. $\endgroup$
    – DKNguyen
    Apr 3 at 2:26
  • $\begingroup$ What do these things look like? Are they dinosaurian? Bipedal apes? Huge cattle-like creatures? Dragon-ish? Body plan greatly affects the kind of tasks they can do, and how practical agriculture will be. Without more, the best I can guess is they would need a lot of animal husbandry and herding, which could be in a relatively fixed place, but also lends itself to nomadic behavior. Also what kind of megafauna and megaflora are there to eat? $\endgroup$
    – DWKraus
    Apr 3 at 5:08
  • $\begingroup$ They are roughly shaped like giant sloths, with a tail for balance and are warmblooded. Let's say there are plenty of large herd herbivores around. There are some deciduous trees and large grasslands around. $\endgroup$ Apr 3 at 12:48
  • $\begingroup$ That's the same weight as 9677-12903 normal sized humans. According to Kleiber's law, They would each need 30.85-38.28 times as many calories than a human. Assuming the average human with daily exercise needs 2340 calories, your giants would need 72189-89575.2 calories every day. Each. 70 to 90 million calories every single day would quickly deplete the local environment, so consider farming food instead. If they lead a sedentary lifestyle you can get away with 55900.2-69363.36 calories. $\endgroup$ Apr 12 at 12:50
  • $\begingroup$ How would a nomadic gatherer lifestyle require more energy than farming? $\endgroup$ Apr 12 at 18:01
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TL;DR: probably not: they need a lot of calories, and it isn't clear how much farming they could usefully do compared to a group of humans with similar calorific demands.

You might be able to handwave away some of the difficulties if they had access to particularly good crops... things like potato, or sweet potato or perhaps sugarcane, but it bears remembering that quite a lot of agricultural tasks really benefit from having human-sized prehensile appendages and giant sloths seem likely to be ill-equipped in that regard. Nomadic pastoralism might be the only practical solution for them (and even then, they probably ain't gonna be making many dairy products!).


For convenience, lets compare your neolithic giants (which sound a bit like megatherium) to large modern day mammals in the form of African elephants.

Elephants are smaller, of course, and not omnivorous, but they'll do as a point of comparison. Somwhere like Zakouma can sustain a herd of several hundred elephants, which means that your 100-strong group is almost certainly sustainable as hunter gatherers.

If your peeps had a similar diet to elephants, they'd be expecting to eat about 5% of their bodyweight a day as uncooked plant matter... that'd be 35 tonnes of food per day, or the best part of 13000 tonnes per year. According to San Diego zoo, that's the equivalent of 140000 calories per day or 586MJ. We know that cooked food yields more calories though we're not entirely sure how much... somewhere between 10 and 50%, perhaps. That halves the amount of food crops that need to be grown but non-trivially increases the amount of fuel crops that are required, and I bet that while the poop of ruminants can be used as fuel, the poop of animals fed a cooked and processed food diet will be less calorie-rich and therefore less useful as a fuel.

I was unable to find useful food-energy-yield estimates for bronze age farming, alas, but I suspect such figures do exist somewhere.

By analogy though, we can see that the largest cities in the bronze age middle east had upwards of 30000 people. If those people managed at least 1500 kcal per day, then the total food-energy requirement of the city would be ~190GJ/day. The equivalent for your giant village would be merely 60GJ/day,

Clearly sourcing that much food is possible with bronze-age technology and organisation, but a city of that size like ancient Memphis was the capital of a relatively large and prosperous society with a total population well in excess of a million people. Feeding a city without such a large agricultural system around it would be a tough proposition. I can't find a hint of how big the agricultural population needs to be to feed a city, but it ain't gonna be small

Your giants seem like they'd be able to do large-scale agriculture more efficiently than humans (they're their own draught animals, after all) but how much this would help is unclear... you haven't given us anything to work with, and I'm not sure how to go about estimating it. If they were substantially more productive than the equivalent number of humans with the same calorific demands (eg. could one of your giants do the work of 70-100 or more humans?) then it is possible they'd be able to farm for themselves.

What might be easier though is some form of pastoralism where the giants practise a certain amount of land management, but have mobile settlements. As (or if) their agricultural techniques improve they might be able to move more slowly or even settle down, but generating enough calories without some particularly good crops seems like it would be difficult.

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  • $\begingroup$ As for prehensile appendages, their hands are a lot more dexterous than those of real megatheriums and are more similar in shaped to human hands, just proportionally big. $\endgroup$ Apr 4 at 13:45
  • $\begingroup$ I find it unclear what I could add to give you something to work with. But I do think your idea of nomadic pastoralism is the best solution. $\endgroup$ Apr 4 at 14:00
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Assuming Your Species has Mammalian like Metabolism:
A T-rex is about the same size as an elephant, and this elephant sactuary has a range of 2700 acres for 5 elephants, or 540 acres/elephant. However, majority of that space is actually needed for psychological reasons. The initial estimate that sanctuary used was 110 acres/elephant, so we know at that is at least enough space to provide enough food. Judging by the photos, I looks like the majority of the sactuary is grassland. Conveniently, this site claims that grasslands have the same net primary production as agricultural lands. In addition, grasslands have the lowest NPP than any other ecosystem your species would realistically be living in. Whether the species is nomadic or agricultural, a population of 100 individuals needs at most 11,000 acres.

Assuming Your Species has Reptilian like Metabolism:
This analysis by a former NASA researcher concludes that 80 hamburgers/day can sustain 15 T-rex. Conveniently, 80 hamburgers is about about 12lbs and a cow beef cow weights about 1,200lbs. Using the latter resource's handy formula, one cow needs ~1.8 acres. That means that 100 T-rex can be supported by 184 acres.

But you didn't ask about T-rex; you asked about T-rex sized omnivores. The vast majority of energy is lost when you go up a tropic level. In fact, ~10% is accepted as a reasonable estimate for how much is preserved. T-rex ate herbivores, which ate plants. This means 1% of the energy produced by the plants makes it to the T-rex. The herbivores however, get 10%. By having your T-rex sized species be omnivores who specialize in plants, you have effectively cut the land requirements to sustain an individual ten-fold! Now, the land required for your village is only 18 acre.

You may be wondering why the first estimate is so much bigger than the second. The simple answer is that mammals are warm-blooded while reptiles are not. Being warm-blooded offers a lot of benefits (e.g. greater temperature tolerance, faster muscles, better senses), but the energy costs are huge.

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  • $\begingroup$ Thanks for the answer! It was very helpful, but I thought that most dinosaurs were warmblooded because a large, active animal would need to be warmblooded to sustain activity. $\endgroup$ Apr 12 at 13:00
  • $\begingroup$ Another thing: i think you need to redo your calcs, because the source from the NASA researcher says that 80 burgers a day can sustain one t-rex, not 15. $\endgroup$ Apr 12 at 17:19
  • $\begingroup$ Your right. I forgot to convert from McDonalds to Hamburgers. The correct answer is 15 time what I gave, ~280 acres. (Am I the only one who loves how dimensional analysis just lets you throw a bunch of random number with crazy units at each other and it all works out) $\endgroup$
    – E Tam
    Apr 12 at 21:17
  • $\begingroup$ I like the idea of them having reptile like metabolism as its very convenient, but could coldblooded creatures become sapient and maintain an active Lifestyle? $\endgroup$ Apr 13 at 12:55
  • $\begingroup$ For a sci-fi story, I'm completely willing to accept a cold-blooded, sapient species. I may not be willing to accept that they act just like warm-blooded animals though. I would want the story to explore how this species lives and develops a society without all the benefits that come with being warm-blooded, including the fact that warm-blooded species can maintain high energy output for long periods of time. $\endgroup$
    – E Tam
    Apr 13 at 16:27
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what can they eat? while I do find it hard to push away from the concept of making them nomadic or at least seasonally migratory, opening up more exotic food options might help them a great deal. Some sources of food might be trees, grass, decaying plant matter. grass and trees are full of cellulose so for they most part they would be pretty sedentary as they don't get a ton of energy fast out of that route, decaying plant matter might be a bit easier on them and their size should help them avoid any major poisoning as well as just things they've evolved. either route however its worth considering giving them a complex or multiple stomachs. Decaying matter would have a lot less cellulose and have the added nutrition of things such as beetles and termites but obviously be lacking else how as a lot of it would be digested by the things breaking it down. You could also take the leaf cutter ant approach and have them farm a fungus that consumes otherwise difficult to break down cellulose. Another interesting Idea might be for them to control large herds of mega fauna herbivores like cattle and follow them to greener pastures, however this proved unsustainable even with things as small as humans so to avoid this they would have to either be able to maintain a really strong population or perhaps have a domesticated version that wastes less energy and nutrition on things like horns or tusks allowing for faster growth with less resources.

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  • $\begingroup$ Their diet is mostly herbivorous, but could eat animal matter occasionally, like real herbivores they can also sometimes eat meat. I agree with most of what you have to say, but following lage herds of herbivores wasnt unsustainable for humans, otherwise the indigenous plains tribes wouldnt have sustained themselves by hunting bison for centuries. It was the europeans who were responsible for the mass extinction of bison to wipe out native americans. $\endgroup$ Apr 9 at 23:19
  • $\begingroup$ oooh true my bad. I was thinking more of mammoths and mega fauna rather than bovine or other ungulates, I gave cattle as an example for how they would herd them rather than what they would herd. If they had a rather large herd of something similar to bison and a large area like the american plains then that most likely would work I just thought in therms of larger creature rather than larger population. $\endgroup$ Apr 10 at 0:37
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It would depend on the size and abundance of everything around them. If their food sources, etc. are as big as them or incredibly abundant, then they probably could.

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