A question about range of omnivorous animals.

Just an idle thought rolling around my head: I can’t think of that many animals (thinking mostly about mammals here) that are omnivorous. It seems like it would be a great advantage, evolutionarily speaking, to have as open a diet as possible. Anyone have an idea why this is not more prevalent? Or, if it is, please steer me to an appropriate resource.

Many thanks,

Pigs, bears, raccoons, rats, etc. Some people even feed their dogs a vege diet(no meat).

There’s a principle in evolutionary ecology that can be expressed as “Jack-of-all-trades is master of none.” In order to efficiently exploit grass as a food resource, for example, requires some complex adaptations to the dentition and digestive system. Teeth suitable for grinding up grass are very inefficient for cutting up meat. A specialized grass-eater will out-compete a less specialized one (that is, all other things being equal, be able to support a higher population level) for that resource.

By specializing on a particular resource, specialists gain access to food that is not available to generalists because the latter lack the necessary adaptations to use it. And it’s simply not efficient/possible to specialize on too many things at the same time.

A raccoon, for example, is not an absolute omnivore, because it can’t survive on grass (and probably not on a pure vegetarian diet). Likewise, it is not nearly as efficient a predator as a cat: It probable would not be able to catch enough field mice or other prey to survive on them alone.

I can understand why certain animals with highly adapted eating styles (say for grass only, nuts only, etc.) would not be able to make much if any use of other food sources. But what about carnivores? Specifically, why don’t dogs, cats, alligators or other animals that consume only (in the wild) meat expand their diet? Why doesn’t my cat go for spring berries like a bear would? It doesn’t seem that predator/carniverous animals would really need to openly compete with prey animals for foods like those.

Your first sentence does not jive with your question: if you understand why certain animals with highly adapted eating styles would not be able to make much if any use of other food sources, then you should understand why carnivores don’t make a habit out of eating berries: they can’t! Because their dentition and digestive tracts are specialized for eating meat, not berries. And it takes a whole suite of morphological and physiological changes to go from “specialist” to “generalist”; very often, specilaization is a one-way street, evolutionarily speaking. Once the trend begins, it is very difficult to “undo”.

Not sure about dogs but cats are carnivores, not omnivores and need red meat to survive. Without red meat in their diet, they won’t get enough taurine and this causes them a whole slew of problems which eventually result in death. Thus a cat already has a specially adapted digestive system and those spring berries won’t do it much good.

You’re thinking of those berries as “free”, but they’re not. It still takes an effort to find the berries, effort to chase off whoever else is picking from that bush, and even some effort (albeit a small one) to actually pick the things. Add the fact that a cat’s digestive system isn’t as good at processing berries as is, say, a bear’s, and the cat would end up getting more benefit from the same amount of effort by hunting.