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I was thinking of a scenario in which a population of snakes gets stranded on an island in which they are literally the only animals. This hypothetical island does not even have insects for the snakes to eat. The island does have dense forests of trees that produce fruit. All the fish and marine life in the water around the island is poisonous to the snakes so eating marine animals is NOT an option for the snakes. The snakes before getting stranded on this hypothetical island have only ever eaten small animals and have never eaten fruit before. Could the snakes on this hypothetical island survive entirely on the fruit that the trees produce? What effect would eating only fruit have on the evolution of the snakes on this hypothetical island? Would the snakes be able to rip fruit from trees on the island or would they have to eat fruit that fell from the trees.

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    $\begingroup$ I think developing an immunity/increased tolerance to the toxins employed by the poisonous marine life is more plausible. That, and/or cannibalism in the short-term. $\endgroup$ – aroth Jan 18 '16 at 7:09
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    $\begingroup$ Have you considered the required pollination for the flowers to get the fruit? Also fruit tends to be very seasonal, what are they eating the rest of the time? $\endgroup$ – Separatrix Jan 18 '16 at 10:39
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    $\begingroup$ Sounds like Lord Of The Flies. Only snakes. Lord of the Snakes. $\endgroup$ – Xandar The Zenon Jan 18 '16 at 17:33
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    $\begingroup$ What's pollinating the fruit trees, anyway? $\endgroup$ – Draco18s Jan 18 '16 at 21:52
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Could the snakes on this hypothetical island survive entirely on the fruit that the trees produce?

The simple answer is "no." A very emphatic "no." Snakes are obligate carnivores. There is no such thing as a vegetarian snake. Snakes recognize fruit as "not meat" and won't consider eating it.

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  • $\begingroup$ and by obligate it does not have the enzymes to digest starch nor teeth to actually eat the fruit. $\endgroup$ – John Aug 10 '17 at 4:19
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All the snakes will die. They will either starve to death or die trying to eat the poisonous fish in the water. They don't have reasoning to 'try' other things, nor is their body likely able to cope with eating materials other than animal protein.

If they were really lucky, one of the fruit might be high in protein and smell enough like a rat or mouse they might try it, and maybe survive. But you would need to invent a fruit along these lines.

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  • $\begingroup$ +1. Also, the fruit needs to have all of the right amino acids. $\endgroup$ – Cort Ammon Jan 18 '16 at 15:49
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    $\begingroup$ Basically, the fruit needs to be meat. $\endgroup$ – Joe Jun 4 '16 at 1:51
  • $\begingroup$ Wait...are fish-eating snakes a thing in reality? $\endgroup$ – Katamori Mar 23 '17 at 18:44
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    $\begingroup$ @Katamori yes, google it. :) $\endgroup$ – bowlturner Mar 23 '17 at 18:52
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Your scenario is problematic and as others have mentioned...everyone dies...errr every snake dies.

The problem with your scenario is that your ecosystem is not scientifically plausible. To have an environment you need each progressively more complex creature to make it all work. You can't just have big trees that bear fruit without, bacteria and other cellular organisms, insects, reptiles, birds etcetera.

It is hypothetically possible that you could stop at the insect level and still have big trees but it seems unlikely.

You need pollinators, though you could argue that this is done via wind...it's not foolproof but if there is no competition among trees I suppose it's possible.

You need soil cultivators, insects and smaller life play a major role in making soil more than dirt/rock. They make it able to support plant life. Without them there simply aren't going to be any nutrients in the soil to make things grow which is the main problem.

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    $\begingroup$ Ya, I didn't go into the the fact that the biome really couldn't exist in the first place... $\endgroup$ – bowlturner Jan 18 '16 at 17:20
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Snakes are supposedly all obligate carnivores. Monitor lizards are their closest lizard relatives (and are pretty close) and they are also obligate carnivores – except for the ones that eat fruit instead.
enter image description here https://www.youtube.com/watch?v=XKfvbvZGz6w

How could frugivory evolve out of obligate carnivory? I bet it had to do with eating frugivorous insect larvae. Lots of protein rich bugs make their homes and lay their eggs in fruit, and a lizard picking those out might have done better just eating the fruit with it.

Could this happen with a snake? Snakes definitely eat worms and bugs and I would not put it past one to eat some bites of fruit as well. There might be an occasional mutant which enjoys fruit for whatever reason, like this whip snake caught on film.

enter image description here https://www.youtube.com/watch?v=CZI3_4EBZW4&t=35s

If it could get enough protein from the fruit diet (maybe from the larvae in them? Maybe from seeds that it could digest?) a snake stuck on this island might found a new line of frugivorous serpents.

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    $\begingroup$ You would need to have the ability to not be an obligate carnivore within the range of genetic variation of the original group of snakes (which seems extremely unlikely in light of the other posts), or you would need some very lucky de novo mutations in your population of snakes (while they eat each other until they go extinct) which is extremely unlikely because you probably need multiple genes and not just one to be capable of subsisting on fruit. To get acceptable probabilities of these kind of mutations occurring randomly in one generation you'd need billions of snakes on your island. $\endgroup$ – ohwilleke Aug 10 '17 at 1:20
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    $\begingroup$ @ohwilleke - There must be some reason they named it Billion Snakes Island. $\endgroup$ – Willk Aug 10 '17 at 11:38
  • $\begingroup$ Good point about the insects in the fruit providing the necessary nutrients that the fruit alone cannot. $\endgroup$ – pojo-guy Apr 15 '18 at 3:01

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