What would be the effect if every vertebrate suddenly died?

Nature Talk
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So, a while back there was a thread about the possible effects if all arthropods vanished.

https://forum.inaturalist.org/t/what-would-happen-if-all-arthropods-disappeared-overnight/55990

But, here’s a question? What if all vertebrates, from hagfish to humans and everything in between, suddenly dropped dead? What trophic cascades would it cause, which other organisms would or wouldnt survive, and how would the climate and soil be affected by all this?

There are two major consequences right off the bat I would think.

  1. A whole lot of parasitic clades go extinct basically overnight. Among land arthropods, fleas, lice, botflies, most if not all hematophagous flies, cimicids (bedbugs) die out, as well as all ticks and a great many other parasitic and commensal mites. Among crustaceans, pentastomids, argulids, and many clades of parasitic isopods and copepods kick the bucket as well. All acanthocephalans and many nematodes die out. Most significantly of all, the entirety of Neodermata, the flukes, tapeworms, and monogeneans, dies out. That is 80% of all species in the phylum platyhelminthes. And this is all to say nothing of the pathogenic or commensal fungi, protists, bacteria and viruses that go out as well.

  2. There is an influx of unfathomable amounts of carrion into the food web. Imagine billions of whales and quadrillions of fish all dropping dead and falling to the sea floor simultaneously, or all the hundreds of millions of land vertebrates in the african savanna. In the short term there will be a population boom of scavenging/decomposing invertebrates of unfathomable proportions, but the long term consequences of this on the biotic and abiotic systems of earth I cannot say.

What do you think?

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I don’t know specifically, but I think the ecosystem might go haywire

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I have to think there would be a pretty huge disequilibrium that would take a long time to play out.

The glut of carrion would be very temporary, and the brief jump in the population of decomposers would surely be followed by the extinction of most of these species. Without vertebrate carcasses and dung to feed on, land-based decomposer species would be limited to food sources no larger than a 4 kg coconut crab. Realistically, almost all carrion would be smaller. I would think most scavenging arthropod taxa would also go extinct in short order for lack of food, with only smallest generalist scavengers surviving, along with decomposing fungi, bacteria, etc.

The lack of vertebrate dung would likely result in changes to soil nutrients in many places, possibly taking tens or hundreds of years to play out. I’d expect that this would cause the extinction of some plant species.

Another group of plants would go extinct because they lose their vertebrate pollinators (e.g. bats, hummingbirds and sunbirds). The “overnight” aspect of the vertebrate extinction makes it unlikely any of those plants would evolve a different pollination system.

Even plants with arthropod pollinators might suffer seed dispersal problems. Already, the animals that ate avocados and pooped the pits are extinct. The depredations of our pre-historic ancestors left behind a bunch of plant species with seeds adapted for consumption by now-extinct herbivores, a situation called megafaunal dispersal syndrome. Imagine the same thing, but on a much greater scale, if all vertebrate fauna blinks out.

More broadly, the annihilation of earth’s megafauna about 12,500 years ago is thought to have caused many cascading impacts, such as a 98% reduction in lateral transport of nutrients such as phosphorus in the Amazon Basin.

Of course, some plants would benefit, too. With no large herbivores, more seedlings would grow to maturity and reproduce. Vigorous but tasty plants might now outcompete species that evolution has equipped with better (now-useless) armor. Predicting which species would win or lose might be tough, but I’d expect that plant biodiversity would be massively reduced.

Even when a new equilibrium was reached (I’d guess that might be on the order of many thousands of years, given the time it takes plant species to disperse and colonize new habitats), evolution would still continue. It would be very interesting to see if, on the scale of tens of millions of years, a replacement for vertebrates might emerge. I guess non-vertebrate chordates such as Lancelets would be spared, so maybe the next conscious and self-aware life form on our planet will trace its heritage to a 5 cm-long “fish” that seized a great opportunity!

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Wonderful and interesting analysis. I think the carrion would last a lot longer in the ocean, since there is way more vertebrate biomass in the ocean than on land. It already takes a very long time for a single whale to be fully processed, now imagine billions of whales, and also quintillions of fish on top of that. Vertebrate scavengers like sharks and hagfish that speed up the process of breaking down dead whales through eating large chunks of flesh will themselves be part of the carrion.

What do you think the long term consequences of in the ocean will be? I think a similar dynamic would playout with scavengers exploding then crashing after the banquet has run out, but it would take longer. But also there is the pelagic zone. With all the vertebrates gone, zooplankton such as krill and copepods would be free from predation pressure. Perhaps their populations will explode to such a point they deplete phytoplankton and then experience mass die offs. Boom and bust cycles.

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Well we sure wouldn’t live to see what happens :neutral_face:

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I think you’re probably right that decomposition would be slower in the ocean, with less available oxygen. Existing studies of whale falls seem to suggest that soft tissues would be consumed in a year and half, and the whole carcass in 50–100 years. Of course, with the vertebrate scavengers also consigned to our subsea charnel house, the initial soft tissue removal phase would probably get extended a lot.

Sadly, the numbers would likely be more modest. Of the 90+ whale and dolphin species, the most numerous is probably the Common Dolphin with about 6 million individuals. The most numerous baleen whale is probably the Antarctic Minke Whale, with about 500,000 individuals. But most species have much lower populations (e.g. fewer than 100 individuals of the recently identified Rice’s Whale). All told, it’s unlikely there would be more than 20 million whale and dolphin carcasses.

As for fish, I found estimates of 3.5 trillion (i.e 3.5 x 1012 ) individual fish, with a total biomass of 10 billion tons. With roughly 360 million square kilometers of ocean floor, that equates to an average about 28 grams of dead fish per square meter. That certainly would cause big booms of scavenging invertebrates and decomposing microorganisms, but it still seems likely that the vast majority of biomass from these dead marine vertebrates would re-enter the reconfigured food web within a few hundred years.

Maybe cephalopods will become the apex predators, with a hierarchy of ever larger squid and octopus species founded on recycling those zooplankton nutrients. Come to think of it, they’re much better candidates than lancelets to become beget the next world-dominating species.

Already octopi have the ability to absorb some oxygen through moist skin and can survive a few minutes out of water. One could see them taking on the amphibian niche pretty quickly. From there, perhaps a slow evolution of a moistened internal cavity for gas exchange (i.e. lungs) would allow them to break free of water entirely. Or maybe they’ll treat the inhospitable land the same way we treat the deep sea and be content with living in the depths and piling their garbage on land!

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More recent studies suggest that fish account for 0.7 billion tons of carbon (about 1.4 billion tons of biomass), so that’s more like 4 grams per square meter of ocean floor.

Overall, animals represent about 0.4–0.5% of global biomass, and vertebrates as little as 0.15% of the total. So at a global level, I think invertebrates (sensu maximo lato) will make a few adjustments and then will get along just fine.

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It is true that animals are a small portion of overall biomass, and vertebrates and even smaller portion of that, but the trophic cascades will nonetheless be significant. I think after the cacophony of scavengers run out of carrion and die out themselves, I think this world might be one that seems quiet and seemingly empty in many areas. It would be quite eerie actually. The endless piles of bones with no great beasts left. Perhaps this is a somewhat more extreme version of what it would be like to be transported to the immediate aftermath of the permian triassic or cretaceous paleogene extinctions?

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There would be the potential for massive climate effects. The actual carbon currently contained in all the vertebrates in the world is probably too small to have an overwhelming greenhouse effect (especially because much of it would sink to the bottom of the ocean) but the ecological effects of removing all the vertebrates might well be a real kick to the carbon cycle. Fish eat the zooplankton that control algal populations. Without fish, I’m guessing algal populations in vast sections of the oceans would go through cycles of enormous crashes and blooms, killing lots of other things and releasing big flushes of carbon. Similarly, I doubt ecosystems such as forests, mangroves, kelp forests, etc. would survive long after a variety of keystone species disappeared. Overall, I will guess that it would release a very large amount of greenhouse gasses very quickly, potentially putting Earth through a global climate-driven extinction. It would be interesting to speculate about how various surviving animals and plants might evolve in the aftermath.

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I am looking at this from the point of view, would other intelligent life forms arise. If so I would nominate the cephalopods, although the social insects might have a leg in as well.

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We see things, not as they are, but as we are.

If we were alive during the time of the dinosaurs, then Pleistocene times would seem eerily quiet.

If we were alive during Pleistocene times, then today would seem eerily quiet.

It’s all relative!

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Humans count?
If so, global warming will stop :wink: and nature will be healthier, but without vertebrates lots of ecosystems will disappear… because of too many invertebrates. :disappointed:

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Thoughts that came to my mind: What happens with all of the things currently being maintained by humans, like power plants, sewer systems and dams, satellites in orbit, that would no longer have that maintenance? Or even the various vehicles in use at the time - huge ships, trains carrying hazardous cargo, planes? Chemical spills, fires sparked by crashes or by systems failing (?), or nuclear meltdowns, even? I too wonder what would evolve in response to all of this sudden, drastic change. Would this “just” be a hard reset, or an end?

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Pretty sure we’re all completely screwed if that happens as we’re vertebrates…

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For some of us, it does! I have driven across the Great Plains, and it does seem eerily empty compared with the documentaries I have seen about Serengeti. If I assume that Serengeti is closer to the evolutionary norm, something is seriously wrong on the Great Plains.

The wildlife around Chernobyl has proven quite resilient. Likewise that in the waters of Bikini Atoll.

As for sewer systems, there might be an initial pulse of contamination, but then water quality would greatly improve because there would be no constant replenishment of the sewage supply.

Dams would eventually silt up, and that would force the water over the rim. New waterfalls and cataracts would form. Erosion would operate the same way as in any place where water flows over rock. Wild rivers restored!

Satellites would burn up on reentry, no different from meteors.

Even the chemical spills from the ships, trains, and planes would be no different from the spills that already happen. There would be new brownfields formed, added to the already depressingly long list of existing brownfields. Without environmental engineers to remediate them, recovery would be slower and untargeted, but in time, natural plant- and microbe-mediated remediation would occur. The amount of contamination would gradually decrease because no new chemicals are being manufactured.

Fires have long been a part of many ecosystems.

No, the demise of humans would be no disaster in the long run. All vertebrates at the same time? That’s a different proposition.

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I imagine it was better when it was native prairie, filled with bison, pronghorn, and other megafauna instead of a “barren corn-ocean of death”, as one YouTube video called it.

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It’s not just an ocean of corn. Here in Western Canada, it’s often too dry to grow corn. We DO have prairie that appears to be native (from 120 km per hour in a car), with pronghorn, mule deer, the occasional prairie moose, etc. But we don’t see mammoths or giant ground sloths anymore.

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In the more Eastern-Central US, there used to be tallgrass prairie, which is extremely flat and fertile, and was converted to farmland. Isn’t what you are describing shortgrass prairie, which is too dry and rocky to be of much use to agriculture?

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Oh I agree that the demise of humans wouldn’t be a disaster for anything other than humans (and if it’s sudden and total, then there is no one to realize it or think of it as a disaster…), and I believe it would unburden the natural world more than anything else. I was just thinking in terms of the sudden loss, what’s left running that might further impact the organisms still here, and does it even matter? I think most things left running in our absence wouldn’t matter much, but I’d never thought about it before and I don’t know for sure.

I know life is amazingly resilient, and is found in even extreme conditions, both natural and human-caused. It’s one thing to deal with Chernobyl, or the various atomic bomb testing sites, but with everything imagined and listed above resulting from the sudden death of all vertebrates, and then add to that all of the nuclear facilities and other human machinery and equipment suddenly unattended, it seemed to me that at least some of what we left behind and running would prolong(?) or increase the negative human impact, even if only temporarily, perhaps only minimally. Just my 2 cents. (-:

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This is how I understand it:

TG vs SG Prairie
TG vs SG Prairie1194×548 88.5 KB

Sorry if this is too off-topic.

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