eli5; Why are all plants not poisonous

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If plants develop to protect themselves in their growth why are all plants and flowers not poisonous?

In: 3

There are special animals that eat poisonous plants, if all plants are poisonous, all animals will be special

Because some (probably most) plants rely on being eaten or touched for pollination and to disperse their seeds.

Same reason why so many humans still have undesirable traits. Evolution isn’t a ladder to supremacy. It’s like stacking a mound of rocks.

Well poison must be produced, so it can take energy and complexity to make the poison. If you’re only being eaten a little bit, it might not be worth it. Also, I think some plants can poison themselves to some extent, or their offspring.

Also, some plants want to be eaten, for instance fruit.

Some also have other defences you might not notice. Trichomes can defend against insects, some plants like radish leaves have an odd texture that many mammals might not enjoy.

Also poison has to be evolved, which can be complicated. Poison could be very helpful, but perhaps other adaptations are even more helpful.

Also, herbivorea adapt over time to poison. Lots of herbivores have evolved to tolerate poisons, so there is a back-and-forth going in, like countermeasures and countercountermeasures, so the poison might not work too well.

There are certaintly lots of poisonous and allelopathic (poisonous to other plants) plants out there though, probably more than you would realize.

For some plants, getting eaten isn’t detrimental to their reproduction. They release their seeds/pollen/etc. once in their lifetime, and then after that it doesn’t really matter if they die. So as long as enough of them survive to the age where they release their reproductive material, then it’s fine if they get eaten and die. Plus many plants follow the “quantity over quality” reproductive strategy that many animals follow: just have a fuckton of babies, and even if most of them get killed because they’re defenseless, a lucky few will survive, and that’s good enough. It’s sometimes not worth evolving strong defenses from predators. Sometimes its better to just pour all your energy into having as many kids as possible.

But also as the other commenter said: all of life is an evolutionary arms race. You evolve some camouflage, your predator evolves keener eyes. You evolve to hide in holes, your predator evolves claws that can dig. This process never stops. No species looks the same today as it did a hundred million years ago. Evolving to be poisonous can usually only work for a time. Eventually the predators will evolve to be immune to the poison. If being poisonous were a fool-proof 100% guarantee of survival, then sure all plants would do it. But it isn’t. Some animals can eat the poison.

Plants do not develop to do something*. The most successful plants fill a niche where there are only few species that eat them, and more species that spread their seeds through eating parts of the plant or through pollination.

A plant that is poisonous to all species won’t survive.

*same goes for animals and partly for humans (humans actively change their surroundings)

So we can eat them, or so other animals can eat them. What would animals eat if all plants were poison? Besides, there’s other means of defense from only specific animals, like thorns and traps. A flower, for example can’t be poisonous, because then a bee can’t pollinate it. But it still doesn’t want to be eaten, so it’s steam has thorns instead. There’s also half poisonous plants, like tomatoes. They’re a fruit,that’s supposed to be eaten, but that doesn’t mean the entire plant wants to be eaten and die, so only the vines are poisonous and hairy.

Toxicity is a relative thing among animals. Chemicals that are poisonous to one animal are not necessarily poisonous to other animals.

For example, grapes are toxic to dogs.

If there was truly universal poison, then the plants that synthesize the poison would also be affected by it.

To add, a plant has to survive against many attackers; animals, birds, fungi, bacteria, virusus, other plants, insects. It will employ many chemical defenses against the worst it encounters, but hasnt got the energy for everything as it must try and grow as fast as it can to outcompete other plants. Its a balance and for some plants being eaten occassionally is a price they will pay.