Omnivores Play For Both Teams
April 17, 2012

Omnivores Play For Both Teams

Just because a bear prefers the taste of flesh today doesn´t mean it has always been so. A new study has investigated the previous eating habits of mammals, particularly omnivores, to discover how their eating habits have evolved.

Large cats, such as lions and tigers are known carnivores, eating meat almost exclusively. On the other hand, other mammals such as cows, deer, and other livestock are herbivores, eating bark, grass, and fruit. Eating a mixture of plants and meat, however, are the omnivores. Researchers with the National Evolutionary Synthesis Center (NESCent) in Durham, North Carolina have discovered things haven´t always been this way, particularly where omnivores are concerned.

Previous studies have looked into animal groups with similar diets and have found them to share certain characteristics. The new study looked at mammals on the whole, across all animal groups, in order to reconstruct their eating habits over time.

The North Carolina team compiled the previously published data for more than 1500 species. This accounts for more than one-third of all the mammals alive today, which includes bats, primates, rabbits, and rodents.

According to their results, some groups of mammals have maintained steady diets, while others have switched from one diet to another over time.

For instance, the omnivores of today – bears, dogs and foxes – come from ancestors who would primarily eat plants or animals, but not both, according to the studies´ co-author Samantha Price of the University of California Davis.

Plant-eaters and meat-eaters alike have been shown, on the other hand, to largely prefer their typical diets, almost never switching from one side to the other. Omnivores, for instance, have switched back and forth from eating meat to eating plants, but have never lost the taste of flesh, always going through a time of carnivore-ism before going herbivore.

Explaining the results in a press release, co-author Louise Roth of Duke University said, “Direct transitions from carnivory to herbivory were essentially nonexistent.”

“It´s an intuitive result because it takes very different kinds of equipment to have those kinds of diets,” she added.

These transitions may have occurred slowly and over time, according to the results.

“Plant- and animal-based foods require different digestive chemistries and different processing mechanisms in the mouth and stomach,” explained co-author Samantha Hopkins of the University of Oregon.

Teeth, for example, need to be suited for different diets. Flat teeth are adapted to crushing nuts and bark, while sharper teeth need to be employed when tearing flesh.

“[Given these differences] it makes sense that you couldn´t easily transition from one to the other in one step,” Price added.

Additionally, the researchers suggest diet could also be linked to how fast these mammals spawn new species. When new species become extinct and others are born, plant eaters reproduce more quickly than their carnivore cousins. In fact, the study shows omnivores lag behind both the carnivores and herbivores.

“If there was an evolutionary race to evolve 100 species, it would take three times longer for omnivores compared to herbivores, and carnivores would be in the middle,” Price said.

The study appears this week in the online early edition of Proceedings of the National Academy of Sciences (PNAS).