IRISH WOLFHOUND SOCIETY OF IRELAND

Q: What is the difference between Herbivore and Carnivore?

(Our thanks to John E. Burchard, Ph.D.,Tepe Gawra Salukis, for permission to reprint.)

Most carnivores (except cats) eat a certain amount of vegetable matter; many herbivores eat some animal matter. This is not theology, where things can be black or white, but science, where all kinds of shadings occur.

The classification of animals into herbivores and carnivores is nevertheless useful and is based on what given kinds of animals use as their primary energy source. Exploiting plants and animals as primary food resources involves different and largely incompatible foraging and digestive strategies, and different animal groups have evolved quite different adaptations as a result.

Mammals (for instance) are classified into orders on the basis of their evolutionary history, and in general the structure, physiology and behavior of animals within any one particular order reflect either a vegetarian or a carnivorous way of life. The foraging strategy and digestive system of animals are generally adapted to using either plants or animals as primary energy sources.

Animal foods generally have a much higher energy content than plant foods, and are much more easily digested. They also tend to come in larger packages. Acquiring those packages demands an active, energy-intensive foraging strategy (hunting) whose relatively high costs are balanced by the large benefit when a food package (e.g. a moose for a wolf pack) is acquired.

Such foods are easily and quickly digested, so carnivores tend to have a short digestive tract with relatively rapid passage of ingesta. The small bulk of the digestive system facilitates the athleticism necessary for carnivores to acquire their prey.

Plant foods generally have a much lower energy content and a much larger proportion of indigestible material. Cellulose, for example, which is an important component of most plant material, can be digested (broken down into its component sugars) only by microbial fermentation - no higher animal, with the single exception of the garden snail, has enzymes that can deal with cellulose. That microbial fermentation requires time, and a large space in which to retain the fermenting material. A long and voluminous digestive tract, and a slow passage of ingesta, are therefore characteristic of herbivores.

Plant foods also tend to be well distributed in space. Foraging strategies of herbivores emphasize the more or less continuous ingestion of small packages which are easily found, don't run away, but also don't contain much energy per package. So herbivores spend a lot of time feeding, in order to ingest a sufficiently large quantity of relatively energy-poor food material.

Fruits are an exception among plant foods. They are rich in simple sugars, easily digested, and largely free of indigestible fibrous material. Fruits evolved, in general, to be eaten by animals. Whereas plants have evolved all sorts of tough fibers, sharp thorns, and acrid chemicals as deterrents to discourage animals from eating their vegetative parts, their fruits have evolved attractive bright colors, pleasant odors and sweet tastes which attract animals to eat them and spread the seeds they contain.

Thus fruits are readily available to, and easily digestible by, even animals with a carnivorous digestive system and physiology. Most reptiles are carnivorous, and so apparently were the earliest mammals which arose from them.

The most primitive of living mammals have AFAIK a carnivorous diet (even eating termites is, actually, carnivory). Several modern mammalian orders include animals adapted to an exclusively vegetable diet. Such are for example the ungulates, the elephants and other Afrotheria, the lagomorphs (rabbits, hares and pikas), and many rodent groups (some other rodents are more omnivorous, and a few actually carnivorous). The Order Carnivora, to which dogs belong, evolved as meat-eating hunters.

Most Carnivora are still primarily predators which obtain the major part of their energy by pursuing, killing and eating other animals. Their body structure and physiology are well adapted to that lifestyle. Bears are commonly cited as omnivorous animals. It is true that bears can and will eat almost anything. The proportion of their total energy budget derived from plant material is, however, surprisingly small. They eat berries in the fall (those are fruit, see above). Most of the energy budget of e.g. grizzly bears comes, however, from gorging on salmon in season, and from consuming in vast quantities the larvae and pupae of a certain species of moth, found in huge numbers on high rocky slopes in the mountains.

They may not spend a lot of time hunting - though they will kill and eat large animals when the opportunity offers - but their diet is predominantly carnivorous just the same. There is one very aberrant and very famous bear which has apparently become not only a true vegetarian, but also a remarkable food specialist. That is of course the Giant Panda. It is, however, in that respect (as in many others) absolutely unique and the product of a long and very unusual evolutionary path.

The family Canidae are more typical among Carnivora. They obtain most of their energy from animal matter, supplementing their diet with fruit in season. Even among wolves, certain populations of which were apparently ancestral to dogs, there is a range of habits depending on the ecological possibilities of their environment. There are few fruits in the Arctic, so Arctic wolves (like Arctic people) are almost exclusively predators, and specialized at exploiting the large animals which are often the only available resource (lemming populations fluctuate too much to be a good resource for a large long-lived predator).

Wolves in the tropics are generally less specialized toward very large prey, having available a greater variety but much lower density of prey animals. Dogs have apparently evolved as camp commensals of human beings, a lifestyle which made available to them food resources unknown to wolves (cooked foods of various kinds, for example).

Ten thousand years is, however, a very short time in the context of evolution, so the dog's digestive anatomy and physiology do not differ much from those of wolves.