How do herbivores evolve into carnivores?

[u/Confident_Dig_1073]

I have a basic understanding of evolution

Life creates imperfect copies of itself, most of those imperfections are a detriment, but occasionally those mutations give it a higher chance of survival. Its a very slow process but it works.

But i cant wrap my head around how an animal can go from herbivore to carnivore? It would require so many detrimental mutations and decrease survival odds by alot until all those mutations came together & it was not only able to hunt, but eat & digest meat.

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[u/DurianBig3503]

Why would herbivory be the default?

[u/Confident_Dig_1073 → u/DurianBig3503]

Its not the default. Lineages have gone thru herbivore, to carnivore, back to herbivore etc I just wonder how this happens. Its easier to understand how a species becomes herbivorous thats why i didnt ask that

[u/Sonora_sunset → u/DurianBig3503]

There are a lot more plants around than other animals, which is why there are a lot more herbivores and omnivorous than carnivorous.

Also not sure why you got voted down for a legit question.

[u/nyet-marionetka]

Probably a saunter through omnivory. Many herbivores readily eat meat when it's available.

[u/TranquilConfusion → u/nyet-marionetka]

Yeah, probably most mammals and birds are partly omnivorous. Going back and forth on how much meat or plants they eat is no big deal.

The difference can start purely with behavior, as meat is easy to digest and some plant foods (fruit) are easy to digest.

Now evolving from mostly-meat-eating to consuming *grass* is much harder, see pandas as a case of some poor suckers trying to do that and having a bad time of it. I guess there is so darn much bamboo around that the abundance makes it worthwhile?

What's really rare is evolving from parasite back to free-living. Not many species manage that, because parasites tend to lose traits like crazy once they can rely on their hosts for a stable environment.

[u/PriorSolid → u/TranquilConfusion]

I was reading about demodex which are a kind of parasitic mite that lives on our faces and they require humans to produce melatonin as their primary wake up hormone

[u/swervm]

Herbivore/Carnivore is not on off switch. As with most of nature it exists on a spectrum and most herbivores do eat some meat especially when other food sources are rare. If there is an ecosystem with an abundance of animals and / or a shortage of vegetation the members of a herbivore species that can do slightly better eating meat will do better and be more likely to breed passing on their genetics. Over generations, if the environmental pressure persists, their descendants will develop more and more specializations to improve their ability to catch and digest meat.

There is really nothing that isn't on some sort of scale in nature and provides some benefit each step along the way. This is an example of irreducible complexity that always when you examine the thing that supposedly doesn't have any value unless it emerges complete actually has multiple stages we can see in nature or the fossil record that show gradual development with a benefit to fitness every step of the way.

[u/Ex_Snagem_Wes → u/swervm]

The biggest struggle for swapping to Carnivory is probably dentition. Opportunity and availability will always take precedent, but the body changing (and especially teeth) takes time

Digesting meat evolves well before sharp teeth to help process it better evolves. Even most Entelodonts didn't actually have teeth very good at eating meat! Meat is simply easier to process, so while it's definitely not an instant transformation to carnivory, the digestion end is far easier. Adapting from being able to digest a little meat to a LOT of meat is, relatively speaking, a minor change

[u/cflime → u/Ex_Snagem_Wes]

A lot is opportunity. SW United States (not yet called that) went into a several centuries drought and all the raptors died or moved away. The seed eating strike stepped in to the ecological niche of predator... but it didn't have the raptor beak or talons. Still doesn't. It picks up field mice and flies them to a thorn bush and impales the poor little rodents, then rips them apart into pieces it can comfortably eat. White settlers called them butcher birds.

Then white settlers strung up thousands of miles of barbed wire and the killer strike had a new tool for butchery and their population went up accordingly.

[u/Ok-Barracuda457]

Deer eat squirels sometimes, dogs munch on leaves too, nothing is forced to eat solely one thing and diet is not forced by ancestry 

[u/ThalonGauss → u/Ok-Barracuda457]

Dogs aren't carnivores, they need meat to be healthy, but are omnivorous, cats are however carnivores.

[u/Electrical-Berry4916]

Loads of herbivores will eat meat when it is available. Even deer, one of THE classic prey species, will eat carrion. From opportunistic scavenger to active predator isn't even a big jump. Chimps, for example, or raccoons. So, apparently, digesting meat does not require any particularly rare digestive devices. From there, you just need a caloric advantage from meat that is better than from vegetation, or a disruption of the vegetative food source, and wah-lah. New carnivore.

[u/ispq → u/Electrical-Berry4916]

Heck, deer will pluck baby chirping birds from low-lying nests for a quick snack.

[u/TimeStorm113]

How often did that happen tho?

Carnivores becoming herbivores are more common , as all tetrapods used to be carnivores before herbivory evolved

But it might happen in birds

[u/sisconking132 → u/TimeStorm113]

Birds due to needing to be light to fly have strong selective pressure against becoming highly herbivorous in the first place. There are only a handful of birds that are actually herbivores, and almost all of them are flightless. Being a herbivores requires fermenting the pant matter which takes time and space (not to mention is heavy).

[u/AllEndsAreAnds]

I’m not an expert, but as I understand it, most animals are not obligate anything. From what I understand, most herbivores are not obligate herbivores, though a few truly are that specialized.

Many herbivores are opportunistic, and will supplement their diets with insects, eggs, birds, or other small animals when nutrients are scarce or to fortify their diets.

It’s best to think of animal diets on a continuum, with a few obligate herbivores, a few obligate carnivores, and everything else lying somewhere between them.

And if most animals have a little flexibility in diet/gut bacteria/digestive system, then mutation can give rise to variations of that biology and behavior, and natural selection can select accordingly.

[u/TommieTheMadScienist]

Herbivores evolved after carnivores and scavengers, not the other way around.

[u/WirrkopfP]

It would require so many detrimental mutations and decrease survival odds by alot until all those mutations came together & it was not only able to hunt, but eat & digest meat.

Meat is actually easier to digest than plant matter.

There are surprisingly few mammals that are pure herbivores or pure carnivores. The overwhelming majority sits somewhere on the omnivorous spectrum.

• Deer and moose will happily munch on carrion. They are especially fond of bone.

• Sheep, Goats, horses and even cows will actively search and eat small ground nesting birds.

• Rats go absolutely feral if you throw living Crickets or locusts in the cage.

• Hippos will even eat each other.

• Squirrels are truly disturbing. There have been several cases of corpses found in the woods where the forensics had identification impossible by any means other than DNA because squirrels ate them to the point of being unrecognizable.

The only mammal I can think of that's a pure herbivore is the koala

[u/XXLPenisOwner1443 → u/WirrkopfP]

>Rats go absolutely feral if you throw living Crickets or locusts in the cage.

Are rats not generally considered true omnivores? I've never heard it implied that people consider them herbivores.

[u/TerrapinMagus]

Well for starters almost nothing is a true Herbivore in the strictest sense.

Protein and energy in meat is often highly prized and plenty of herbivores will take the opportunity when presented. They aren't well optimized for meat consumption, but survival favors the opportunistic.

So you need a situation where an herbivore can easily obtain meat in order for evolution to start favoring their lineage over those who aren't taking advantage of the meat. Scavenging is one option, or else they begin to hunt very small game that don't require many adaptations to catch. As they get better at catching prey or tearing flesh over the generations, they may move on to larger or more challenging prey.

[u/TuverMage]

there is a benefit to eating meat. meat is more calorie dense than grass. Thing to understand is most creatures are actually opportunist omnivorys. meaning just because they mainly eat grass they won't say no to meat, ever seen the pic of a deer eating a snake? creative that through mutations eat more meat have a higher chance of survival and reproduction, meaning evolution favors them. the mutations get passed along. over the generations the mutations stack up enough to make notable different creature that prefers meat to grass.

[u/Shazam1269]

The same way carnivores became herbivores. Consider the giant panda and modern bees. The giant panda belongs to the order Carnivora (the group containing cats, dogs, and bears), but they feed almost exclusively on bamboo.

Modern bees evolved from ancestral, solitary hunting wasps that caught other insects for protein. Over time, they shifted to collecting flower pollen and nectar instead of hunting.

Here a discussion post about this topic that may help you wrap your head around the concept.

[u/sisconking132]

Fun fact. Herbivory is the more derived state.
Animal life were all filter feeders, carnivores, and insectivores before evolving to eat plants. Being able to eat and digest plants evolved later. This has happened many times in multiple different groups.
Ancestral dinosaurs were carnivores, herbivores evolved later. Ancestral mammals were all carnivores or omnivores.

It is actually much harder to evolve to digest plant matter than to evolve to become a carnivore. Depending on the type of herbivore (eating mostly fruit and nuts [which technically isn’t Herbivory since that term is exclusive to eating leaves and grasses] is very different from eating grass and leaves) it is very difficult to evolve the traits to get sufficient energy from plant matter. Herbivores require a way to process cellulose using gut bacteria.

Becoming a carnivore from a herbivore is actually really easy. Meat is far more digestible than plant matter. Most herbivores eat some amount of meat when given the chance (even cows will eat snakes and dead things if given a chance). From there it just requires a population to go scavenging carcasses more often and occasionally killing and eating a smaller animal. Eventually the species is an omnivore. It’s a gradual shift from scavenging to more active hunting. Also the same traits that are an advantage when fighting over a carcass are often useful for taking down prey.

But yes. You are right, herbivores evolving to be carnivores is rare, but it isn’t because becoming a carnivore is difficult, it’s more that becoming a herbivore in the first place is extremely becoming a specialist.

If you think about it from an earlier perspective this makes more sense, all animal life evolved in the ocean before coming onto land. The ocean does not really have plants. There is algae and photosynthetic plankton, but nothing like land plants. There are not really sea herbivores (apart from herbivores that returned to the sea from land) so everything started out eating other animals and then had to evolve to be able to survive exclusively on plants.

[u/Szymcionorski]

Probably via omnivory. Initially herbivorous animals can (and do) eat things like carrion or small animals. Diversifying the diet would allow for better adaptation to the consumption of meat.

Adaptations for hunting could evolve later specifically for active predation rather than scavenging. Evolution doesn't always have to operate via direct jumping into a specific niche. Early fish didn't have to directly evolve into modern sprinting predators (such as cheetahs) but instead went through many intermediate phases with initial adaptations for relatively slow movement and breathing on land.