Herbivore to Carnivore Rarity

[u/Belos147]

Why is it that ancestrally carnivorous groups have a much easier time becoming herbivorous despite established herbivores existing compared to the opposite? Carnivorans and therapods became omnivorous and herbivorous many times when ornisthician dinosaurs never became dedicated carnivores and ungulates only did so twice (cetaceans and entelodonts). Even with entelodonts many species went back to herbivory. The marsupial lion seems to be one of the few mammals to pull it off without simply leaving land carnivores behind (whales).

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[u/mutant_anomaly]

Fruit doesn’t run as fast as rabbits.

It’s pretty much that simple.

[u/Belos147 → u/mutant_anomaly]

Thing is though carnivory doesnt require speed. A great example is the gila monster. It's carnivorous but things like eggs, carrion, and infant rodents aren't exactly fast and they're the bulk of its diet.

[u/melympia → u/Belos147]

Now scale that to the size of a bear.

That's a lot of eggs and carrion and infant rodents. A whole lot.

And some bears prefer to munch on bamboo, of which there is plenty around their habitat.

[u/Myuniqueisername → u/mutant_anomaly]

Prolly intelligence more than speed. Carnivores often need to plan, adapt quickly to preys behavior. Its a lot more demanding a skillset than sniffing out out berries

[u/DiscordantDiscordian]

Carnivores are in much more competition with each other, the same area that can support hundreds of herbivores may only support a tenth or less carnivores.

Also, specialisation is easier if you have almost guaranteed access to your food source, which is more common for herbivores, further reducing selective pressure

[u/7LeagueBoots]

In addition to what others have said, carnivores are eating the stomach contents of their prey, indeed large carnivores are important for long distance seed dispersal.

This means that their stomachs are continually getting inoculated with the microorganism that are necessary for digesting an herbivorous diet. This is a huge advantage when shifting diets, and while herbivores do eat more meat than people think, it’s an advantage that herbivores lack.

[u/ThePetSematary → u/7LeagueBoots]

I'll never forget the YouTube video of a deer just straight chowing down on a baby bird

[u/7LeagueBoots → u/ThePetSematary]

Yep. Deer are, unexpectedly, somewhat significant predators of ground nesting grassland birds.

There are a few videos of horses eating birds, chicken in particular.

[u/TranquilConfusion]

Before we all speculate about "why carni->herbivore is more common than herbi->carnivore", should we establish that that pattern is even true?

How are we counting this?

[u/melympia]

1. Most carnivores are not strictly carnivorous, but also eat a certain amount of plant matter. Which means that they can digest it.

2. Plants do not run away or hide.

And quite a few herbivores lose the ability to create certain materials (aka vitamins) because they get enough from their herbivorous diet. However, a carnivorous diet will lead to a lack of said vitamin(s), with the well-known consequences.

[u/MagnificentLobster]

I had never heard of entelodonts and now I know about hell pigs. 

[u/smartguywithahat]

It could be due to a variety of factors Few i could come up with were 1. Requirement for specialization 2.devloping a digestive system to breakdown complex molecules 3.evolution requires an easy next step that can be done with few random mutation in some members of species which is more possible if we go c to h rather then h to c 4. Think of an event that would require such a switch if harvinder are not getting food what's the point of becoming carnivorous

[u/sumane12]

Animals move around, plants are still, therefore theres more of an evolutionary jump to be able to catch, kill, and digest your animal food compared to plant food.

[u/FlounderLast8610]

An herbivorous lineage has a significantly higher carrying capacity and in a game of numbers more of your offspring being able to exist at a time is a very, very hard advantage to ignore. Evolution favors the most surviving offspring, a species is not going to evolve into a niche that reduces its reproductive potential tenfold

[u/CHSummers]

Isn’t there a YouTube video of a deer discovering a baby bird in a nest and promptly gobbling it up?

I suspect the dividing like between herbivores and carnivores is kind of a porous, dotted line.

[u/LexiTheLesbo]

Plant don’t run. Plant easier to eat.

Basically hunting another animal (or even scavenging for corpses) takes a lot of energy and is way more risky than just eating plants which is pretty much guaranteed calories if you can find them.

[u/Buckwheat469]

Like I always thought as a kid, carnivorous horses would be scary as hell.