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[Descan]

I decided to change this topic into a game of sorts. I'll post a question, and hopefully people will hash out "what would happen if" that situation came to pass.

The first question was "what would happen if all macro-scale animal life except caribou were to disappear?"

The second question was "what would happen if humans colonized three planets in a system, then they all reverted back to the stone age, with a new technological build-up on each planet? Finally meeting each other at an equivalent of our modern era."

[Descan]

...

:c

[da_nang]

XKCD would probably give you a more interesting answer, but if I had any say on it, there would probably be a lot of plant-life dying due to lack of carbon dioxide. Bacteria will probably stave some of it off as they break down dead organic matter, but still, there simply wouldn't be enough carbon dioxide.
And if they don't die from lack of carbon dioxide, there's always explosive caribou population growth combined with climate adaptation...

[Cthulhu]

Any species dependent on animals for seed dispersal or other functions would probably die.  There might be places that survive, but I'm guessing you'd see massive ecological upheaval and possibly collapse.

[Starver]

As far as the Caribou Question^TM goes [albeit now slightly ninjaed], without predators and competitive grazers, I can only imagine that there'd be an explosion in the caribou population around where they currently reside, before there's too many of the other, following effects, and an inevitable spilling out into (compatible) neighbouring biomes due to just the same relaxed pressures...

But even without macro-species, there'd still be diseases and illnesses, and with a larger population, it would spread.  Plus (as has been seen, e.g. in Yellowstone post Wolf-eradication and only now post Wolf-reintroduction being undone) they're depriving themselves of their fodder by their own verdant nature.  So sickness and starvation and death shall probably ripple out from the epicentre of the newly enlarged and spread population.

Of course, natural selection loves this kind of situation, and there'll be some that are better adapted for the leaner times.  Perhaps making use of plants that have not been traditionally eaten by caribou (whatever they might be), and you'd end up with a spread-out and (probably) thinned population that has an 'event horizon' to gene-transference, meaning that you'd get the very beginnings of speciation starting...  but it wouldn't be soon.  (Also, it'd take longer, or at least be less likely to be soon, for one particular form of post-caribou to adopt to meat-eating, even just of discovered carrion (of which I'm suggesting there'd be plenty).... Besides the fact that carrion eating needs its own set of developmental changes to handle non-fresh flesh, even compared to switching to a more generic carnivorous digestion along with the teeth and claws 'upgrade'.)

Alongside that, there are doubtless some plants that initially benefit (especially in still 'non-cariboued' area) from population explosion, even while others lose out due to being co-evolved to require prorogation/support by some other species (even ignoring humans and their crops, and do we involve bees and other insects under the 'macro' flag, or not?).  But overpopulation of the benefiting plants (and under-provision of CO2, until things adopt and adapt, although over-oxygenation would probably also lead to a rise in forest combustion, leading to a different level of atmospheric equilibrium) would also lead to a similarly following population crash and possible re-diversification, although perhaps on a different 'biogeological' time-scale and area to the neo-caribou development.


Personally, I don't think the situation will resolve itself by recreating a brand new ecosystem (from carbou-dolphins and caribou-cheetahs and flying-carbou and burrowing-caribou, onwards, perhaps even unto Caribou Sapiens?) before the situation completely falls over and leaves unsustainable micro-populations (of caribou, if not of vegetation) in the ruins of the once great herds...  But it might...  (Just probably won't.)



I could follow up with one of my many questions, but I haven't given up on Google and its ilk, yet, so wouldn't be fair to the given premise.

[mainiac]

Humans wouldn't die of protein deficiency without livestock.  Vegans do exist, y'know.  This should tell you that a vegan diet is possible.

[Descan]

Hyperbole~

[Gantolandon]

Such as this one: What would happen if every single macro-animal species on earth, except for one, were to disappear? All the grasses, and plants, and trees, and such would stay around. And... let's say caribou. Caribou is the only surviving species. What would happen? Both in the short term and long-term, assuming there -is- a long term and the be-antler'd northern species didn't die out.

A lot of plants need bees and other pollen-gathering species to reproduce. Others use animals to spread their seeds. These, of course, would die out. And that's the only thing I'm really sure.

I think the result would be a total clusterfuck. Predators and diseases, for example, prevent overpopulation - unchecked caribous would soon spread and eat all the plants that could be eaten. At long term, unless they adapt really quick, they would destroy most of the remaining, available plant life, then suffer a mass die-out. So the only plants that have any chance to survive are those which are not dependent from animals and hard to reach. It's not very much.

[Starver]

I'm more optimistic about the plants, Gantolandon, perhaps get something like a New Carboniferous, or a "Hothouse"-type world, although rising oxygen levels (as already mentioned) with little initial CO2 return[1] would bring us into an age of more out-of-control forest/grassland fires, etc.  Some plants thrive on (even require) such events, and I think adaptations to a (virtually) plant-only ecosystem would be proportional (though not equal) to the plant extinctions due to loss of essentially symbiotic animal partners (either directly or "as a heavily breathing mass").

I'll actually expand my answer to suggest that if plant-life is left (initially) untouched by the "all-but-the-caribou" catastrophe, then I can still imagine a vibrant plant-only (and fungi, and of course all other non-macro life-forms that are allowed, probably bacteria) ecosystem continuing...  Again, "Hothouse" (look it up) comes to mind, but I'm trying not to be inspired by pre-existing art on this subject.

I'm not saying that a different result would not be better for plants, e.g. "everything animal (including insects) but bees departs the ecosystem in one fell swoop", perhaps.  That's be interesting.  Because I'm betting that with the increased oxygen levels you could get bigger bees, and (again) diversification of the bee populations across other ecological functions, including aquatic bees...  I could even see there being "bee-whales", after a long enough redevelopment phase of a particular sub-tree of the apicultured result.  (A long, long time..., and it would be a random possibility of jostling into a possible niche, not an aim, of course.)


And I've answered all these questions as if Humans are absent, or at least hands-off and happy to observe the result without interference.  With humans still around, I predict war over resources, which is much more likely to send the planet into a more lifeless 'dead rock' mode.  (Although I would imagine that "life will out", even if A-bombed back to "living in cracks in the rock, barely multicellular even".  Again, long time periods would help heal the crisis and with a very long waiting time we could expect it all to look 'naturally diverse' again, some time in the future.  Assuming it arises before solar expansion takes out this little fragile outcrop of life on this insignificant grain of sand, etc, etc, of course...)

[1] Various forms of rotting, some plant respiration, and the fires that I mention shortly after this footnote call-out.

[mainiac]

Gantolandon, even if only 1% of plant species survive, that's a lot of plant species.  And it seems that you are implying that without predators of their own the caribou would eat all the plants and have nothing left to eat.  Predator prey relationships are more stable then that.

Starver, we would not see an appreciable increase in the amount of atmospheric oxygen because there isn't that much CO2 in the biosphere to turn into oxygen.  There's more then 40 times as much O2 in the atmosphere then CO2.

[Descan]

I have the sudden urge to create a world of a single species descendants a la The Future is Wild, and create such a tour of that world...

[Eagleon]

Deer can already eat meat. You're welcome for the nightmares. According to the Internet, they'll also eat bird eggs, char, and lemmings. Deer (not sure about reindeer) love kudzu, too, which spreads like wildfire by runners. That would probably spread south past where the caribou would be willing to go, which would maybe provide some sort of equilibrium. It'd be a boring ecology, but North American caribou would most likely be fine after an initial growth explosion and rapid selection for metabolism and physical capability - no predators means they'd probably end up looking very strange before long, maybe closer to sloths and drastically smaller or larger depending on what plants they're eating, carefree and stupid except for disease.

Also, plants don't necessarily require much CO2, and we probably wouldn't see a drop fast enough to be significant. This is a succinct overview - most of the animal-sourced CO2 is from microorganisms, though some of those would undoubtedly suffer. Much worse for them would be the enormous deficit of organic matter insects (and their food sources) produce.

[DeKaFu]

Something that hasn't been brought up yet.
In this situation, massive caribou overpopulation and subsequent die-off from starvation is a given (stuff like that already happens when predators are removed today).

So now you have a lot of dead caribou. And what don't we have? Vultures. Flies. Carrion beetles. Scavengers of any kind.

For that matter, we'll have a lot of plants dying in the natural course of things, and we'll be lacking insects and worms and slugs and things that would normally be converting the vegetable matter back into nutrient-rich soil that other plants could use.

Bacteria and fungus (do we have fungus?) will do their part, but a ton of the nutrients and chemicals that make up living things and are required for life are basically going to be locked up in dead stuff and removed from the playing field. The various cycles turn into one-way streets.

Everything everywhere is going to be screwed.

[Flying Dice]

Also note that the conditions only specify an instantaneous die-off of all save one species of macro-scale animals. Domains Bacteria and Archaea? Doing great. Five of the six branches of Domain Eukarya? Just swell. Every subgroup of Opisthokont except Animalia? Spiffing, old chap.

So at the very least we've got all of the bacteria, so even if through some freak coincidence all of Plantae and Fungi, and the various harder to pronounce subgroups, died off somehow (eaten by a living ocean of caribou?), we'd be back to macro-scale life in a few hundred million years at most. If even a small selection of plants, etc. survived, it would be a much shorter period of time to get back to animals.

Incidentally, would everything just disappear, or would all the corpses be there? Because corpses be plant steroids, yo.

[Ancre]

Well, if humans survive, we'll have to live on caribou burgers and caribou bacon. Kitchen is going to become a lot more boring.