You are assuming that they haven't.
Brambles can trap sheep, benefiting from the sheep as fertilizer: https://www.youtube.com/watch?v=mrGobnZq83g
Falling coconuts can not only kill people, but probably kill far more small animals, again benefiting from them as fertilizer,
Reminds me of a semi-plausible mechanism for carnivorous flora from this [0] Worldbuilding Stack Exchange answer by ckersch:
> Bonegrass is a white fungus which grows in wheat fields. Most of the time, the bonegrass fields are normal wheat fields, indistinguishable from other wheat fields except for their exceptionally high yields and relatively low numbers of animal inhabitants. Of course, this entices lots of animals, large and small, to move into the area. Populations boom, fueled by the seemingly unnatural abundance of the wheat.
> And then the bonegrass blooms. Overnight, huge mycelial mats below the wheat fields become active, with white fungal growths growing up the stalks of the wheat plants, using their stalks for support. Then, simultaneously across hundreds of square miles, the bonegrass releases its paralytic spores. Within 12 hours, the wheat fields become pale, white places of death. The fungus then begins to grow over the paralyzed creatures, flooding their body with neurotoxins that keep them immobilized until they die from dehydration over the next few days.
> The dead animals quickly break down, broken apart by the fungus. As suddenly as the bonegrass grew, it will then die back, shrinking back beneath the earth, where it will slumber as the land above it slowly repopulates, drawn by the seeming gaia above the soil, and unaware of the horrors slumbering beneath...
Scary stuff. Symbiotic plant-fungi or plant-bacteria relationships seem like plausible mechanisms for "carnivorous" plants, even if it's not "plants directly eating people" a la Little Shop of Horrors. There are more good answers with a similar premise under the same SE question.
[0] https://worldbuilding.stackexchange.com/questions/38354/how-...
I bought a tiny Venus Fly Trap once, left it in the kitchen, and went away for a weekend.
When I came back the kitchen was buzzing with flies, and the plant had literally gorged itself to death.
This was extra impressive because none of the windows were open. It had somehow leaked attractant scent through gaps I didn't know existed and the flies - not exactly numerous where I was - must have been aware of it from hundreds of yards away.
Point being the plants may be small, but they can be very good at what they do.
As soon as a carnivorous plant gets big enough to be eating young mammals, it hits the Mama Bear barrier. With motivation, even a tiny mammal can do an enormous amount of damage to a plant.
I would have thought that plants which ate neighboring plants, for their easily accessed nutrients and to protect their own access to sunlight, water and forest nutrients, would be pervasive.
I have heard of chemical/strangling/parasitical type competition. The banyan tree is territorial, for instance.
But we would need another name, other than territorial, carnivorous or vegetarian, to describe plant predators which overtly, actively fed on the physical structure or leaves of fellow plants.
We haven't had an unscheduled total eclipse of the sun with people singing in the background yet.
Larger animals tend to more intelligent - presumably there’s a natural limit to the size of prey a carnivorous plant can reliably catch from a static location.
OK, let's see. You're a plant, so you have photosynthesis. It allows you to tap around 5W (averaged out) per square meter of foliage by just AFK-ing. Your major need: water, you have to evaporate it for the photosynthesis to work. But it's not a problem in your habitat, there's plenty of water available.
You also need nitrogen, phosphorus, and other nutrients, but comparatively little of them. Nitrogen is the toughest one. This is the one that you can easily get from animals, though. So you can evolve a complicated mechanism to trap small animals and digest them for nutrients. It also provides you with a bit of energy, but it's completely immaterial compared to photosynthesis, so you don't even bother evolving all the complicated protein-to-glucose pathways.
Now, you want to grow bigger. How would you do it? Energy is not an issue, the photosynthesis provides plenty of it. But you need to trap more or bigger animals, and that's an issue. There just aren't that many of them, and you can't just get away with simple traps anymore.
The article doesn't seem to talk about it but many carnivorous plants lost part or most of their chloroplast genomes: https://pubmed.ncbi.nlm.nih.gov/30629170/
I.e., because they got their nutrients from animals they didn't need chloroplasts and the chloroplasts 'broke' over time. Chances are minimal to zero that carnivorous plants will regain chloroplasts. In a way, carnivory in plants is an evolutionary 'dead end' similar to parasitism, which is also often linked to chloroplast loss. Where could the plants evolve 'to' if they have no chance of getting energy from alternative (chloroplast) sources?
>Most of this carnivorous botany is small, but the diversity of different trapping mechanisms raises an evolutionary question.
Isn't the obvious conclusion that: 1. There are many peaks in the fitness hypersurface for plants that correspond to meat eating 2. The peaks have smooth gradients at the outskirts 3. All peaks are minor local maxima
1 is because low nitrogen alone is not enough to make carnivory a net positive contributor to fitness. You need additional factors to make the gradient positive to begin with. That means the peaks (niches) are random and narrow.
3 is because carnivory implies an arms race against prey defenses, competing scavengers, and competing predators. Specialist animals are at a large advantage against plants, especially if meat is still a side dish to sunlight.
To me the interesting question is 2 - most plants don't digest animals at all, so how does this begin to evolve?
> Some large carnivorous plants are alive out there, but none is big enough to make a meal out of you.
Clearly these researchers have never been to the Mushroom Kingdom.
How about: larger animals can learn from seeing others eaten, so they won't fall for the trap.
A related question is why plants in general can thrive on such tiny amounts of protein. (Nitrogen)
Plants not being able to chew or tear their prey is a big disadvantage.
I guess there are still some things that we can be grateful for.
One day it'll The Day of the Triffids
Because a fly can spit on your food, but a mouse can eat a hole in your baseboards.
I used to think carnivorous plants would someday grow huge and eat people like in the movies. Turns out they have always stayed small and just got really clever instead.
This piece made me see it differently. Not growing big is not a flaw. In a place with barely any nutrients, surviving with just a bit of strategy is actually kind of amazing.
tl;dr Basically a lot of sorry excuses.
If you're a plant, don't buy into the negativity. Work your way up the food chain. If you eat it, then it's your food.
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OK, I wrote my theory, and then read the article: same.
But I will add that a commercial grower of venus flytraps once got curious, and took a few thousand cloned plantings, growing them in a variety of conditions. As soon as the soil became nourishing, the plants would die. Post mortem seemed to indicate their roots were fungally attacked.
So: plant adapts to living in a food desert (not an actual one, of course; it has to be wet for the carnivory to work, as the article points out). Plant gains weirdo digestion abilities, but at the same time, it no longer needs expensive anti-fungal defences - because the ground isn't rich enough to support parasitic fungi.
Then: human adds the nutrients back in. Boom! The ordinary fungus in the air, which has a tough time invading grass or tree or tobacco or pepper roots (because they have extensive defences, like capsaicin), lands in the rich soil of pretty-much helpless flytrap roots, and has a buffet.