Omnivory versus obligate carnivory/herbivory.

I’m thinking about the K-T mass extinction event, where it seemed that land-dwelling omnivores stood a better chance of surviving this most turbulent of shit-storms than did obligate herbivores and carnivores over a certain body size. To the extent that I understand biology and ecology, I figure there’s got to be advantages to a specialized diet over a more broad diet, but I can’t figure out what those might be.

I don’t understand your question. You start out saying that omnivores had a better survival chance, and the speculate the specialized eaters should have some advantage. Why? And are you sure that ominivores better survived the K-T extinction event? Seems it was more an issue of size, and the biggest animals tend to be herbivores.

Evolutionary advantages are a function of the environment. They can’t be discussed without that context. If the environment consists of only one food source, it’s an advantage to not want to eat anything else. But that would be an odd situation…

From my ass, with love: I would imagine that the wider a variety of food that you are able to eat, the more energy your internal machinery takes to run and maintain. You need a wider variety of organs/longer intestines etc. Basically you have to have the adaptions for both, which is probably difficult to keep going.

Cats, for example, have short guts. They don’t need long ones. That’s an advantage, energy wise, and saves them from certain kinds of poisoning, but it means they don’t get as much out of their food and have to eat energy-rich meat. That’s why the dog likes to eat cat poop.

Laudenum: Cats and other carnivores have short digestive tracts because what they eat doesn’t require as much processing to harvest. Herbivores have longer digestive tracts because it takes longer to turn low energy plants into compounds that they can use to build into themselves. Omnivores land somewhere in the middle length-wise.

The amount of energy needed to run either set of guts depends on how you calculate it. Herbivores utilize bacterial reactions much more than carnivores. Are you counting all the energy used there, or just the energy to move foodstuff along and absorb nutrients?

Zsofia: What kind of poisonings are you thinking of? Because I can’t think of any particularly that would get an herbivore but not a carnivore due to GI transit time. I can think of one that only work in herbivores because they accidentally process it into a toxic compound (photosensitization from certain plants during certain times of the year). Depending on the plant, a carnivore randomly munching on those plants wouldn’t get the same toxicity. But, that doesn’t depend on GI transit time.

To the OP: like John Mace said, judging the pros and cons of a particular evolutionary tactic depends entirely on the environment in question. Being a specialty feeder works pretty well if what you are eating is plentiful and no one else eats it. Witness: Koalas, pandas, parrot fish, crossbills, etc.
In short, this isn’t a simple question and judging the worthiness of a particular biological system requires discussing lots of parameters in the context of environment.

If you are wondering why we have specialized feeders when it seems less likely that they would have survived the K-T event: that was a while ago. Immediately after it happened, stuff would start re-specializing again.

Come to think of it, that was a really poorly-formulated question with a lot of poorly thought-out assumptions. Thank you and my apologies. I was trying to understand just how specialized diets came about. That sort of diet seems particularly vulnerable to environmental changes; if your food source dies out, so do you. But that’s been answered already.

So, after a mass extinction event or other massive sudden environmental change, selective pressures likely favored small size (and correspondingly less food needed). Omnivory may or may not have been a part of it; most larger organisms tended to be herbivores. But as soon as things return to equilibrium, specialization is once again favored, because that reduces competition for resources between species. Does that about sum it up?

No worries :slight_smile:
Even when discussing massive environmental change, predicting what the likely evolutionary responses are requires taking the specifics of the environmental change into account. But, yeah, odds are that most scenarios would tend to favor omnivorous, smaller critters. If the massive environmental change is the introduction of a particularly aggressive and delicious kind of bamboo, then pandas will reign supreme.

Yup. The main thing to remember is : evolution doesn’t plan ahead.

A species doesn’t specialize to survive in or adapt to all possible environments, it specializes because it has managed to survive in the same environment for a long time, and “learned” to take the most advantage out of it.
Being a jack-of-all-trades might let you spread over a wider variety of environments and compete for a wider range of resources, but that doesn’t help if you’re number 2 in all of them. Of course, on the flip side the more you specialize, the more screwed you are when the forest become a strip mall overnight. But come on, how often does that happen ? :wink:

I guess not poisoning per se - I’ve been told that a reason our carnivorous pets can eat meat we wouldn’t eat is that it isn’t in them as long, but whoever told me that may have been oversimplifying for me.

I don’t think it’s correct to say that specialization was “favored”. Rather it was one possible survival strategy that worked. Look at the situation with polar bears and grizzlies. They are very closely related and sometimes interbreed in the wild. They split off from each other only about 150k years ago. And yet the polar bear is a pretty specialized eater while the grizzly eats almost anything. Guess which one is expanding into the others’ territory during this current time of climate change?

You have to live in a pretty stable environment to be a specialized eater.

There’s also the point that almost all animals are omnivorous to some degree. Grazing animals, for instance, will eat anything that doesn’t get out of the way as they move slowly over the grass. Most animals will get out of the way, so their diet ends up being mostly plants, but they’ll also “graze” on any animals that don’t get out of their way. It’s like that old saw that “vegetarian” is an Indian word for “lousy hunter”: They’re not vegetarians because they actively avoid meat; they just lack the adaptations to make them likely to be able to get much.

Yeah, I dunno about that. Cats and ferrets can get food poisoning just as much as we can from spoiled flesh. Similarly, we could probably eat a lot more raw meat then most of us normally do without getting sick every time. So, I don’t think a cat or ferret has any special immunity to low-grade meat compared to us.
They certainly have lower aesthetic standards for flesh.

True scavengers, like vultures, do have an increased resistance to pathogens found in spoiled flesh.