Dissecting the animal diet, past and present

March 18, 2016
A still life of grizzly bear (Ursos arctos) with diet inferred from multiple proxies, such as isotopes of hair, teeth, and blood. Credit: Peabody Museum of Natural History/Yale University

Researchers at Yale and the Smithsonian Institution say it's time to settle a very old food fight.

In a study published March 18 in the journal Ecology and Evolution, authors Matt Davis and Silvia Pineda-Munoz argue that scientists need to focus as much on "when" animals eat as they do "what" animals eat. Without the proper time context, they say, an animal's diet can tell very different stories.

"Diet is one of the most important features of animals," said Davis, a Yale graduate student in geology and geophysics. "But often, we can't seem to agree on what animals ate. Grizzly bears, for example, eat different foods at different times. If you looked at their diet in the spring, it would look like what wolves eat, but in the fall, bears eat mostly seeds, just like squirrels."

Researchers use diet reconstructions to provide crucial information for managing habitats of endangered species, understanding evolutionary changes in species' function, and describing ancient habitats and climates. Routinely, this bit of diet detective work is achieved with dietary proxies: chemicals in hair or blood samples, dental remains, stomach contents, skeletal analysis, and measurements of feeding sites, for example.

Yet often, diet proxies don't agree. This is because each one records what an animal eats over different lengths of time. Chemicals in hair, for example, may offer information about nutrition over the course of several years; stomach contents would reveal perhaps a week's worth of meals. Each could give a different answer for what an animal ate.

Davis and Pineda-Munoz give examples of how such disparity can be problematic in research. In one instance, scientists unintentionally reversed the order of a food chain in a lake in East Africa because they hadn't factored in the different speeds that zooplankton and their predators absorb nutrients. In another, researchers thought that certain regions of ancient Africa were covered in forests because they assumed the fossil elephants they found there ate mostly trees, just like modern elephants; however chemical analysis showed the ancient elephants actually ate mostly grass, so the "forests" were most likely fields.

"The correct diet proxy depends on the question you're asking," Davis said. "We can't just look at stomach contents sampled yesterday and extrapolate them out for 1 million years."

Davis and Pineda-Munoz suggest that researchers explicitly state the time scales for the diet proxies they use to avoid confusion. They also call upon scientists to consider the effects of time scale at each stage of their research.

Pineda-Munoz points out that the different time scales can actually be helpful to research. "By using different proxies like the chemical signatures in feathers and blood we can tell not just what a bird is eating but what it ate a year ago and how its diet changed since then," she said. "This is especially important for rare or endangered species because we can effectively time travel through their without harming the animal."

Explore further: Research calls for a new diet classification for mammals

Related Stories

The evolutionary link between diet and stomach acidity

July 29, 2015

An analysis of data on stomach acidity and diet in birds and mammals suggests that high levels of stomach acidity developed not to help animals break down food, but to defend animals against food poisoning. The work raises ...

Change in early human ancestor diet came earlier than thought

September 15, 2015

(Phys.org)—A team of researchers in the U.S. has found that our early human ancestors expanded their diet to include savannah grasses and other food sources approximately a quarter of a million years earlier than had been ...

Reef sharks prefer bite-size meals

February 22, 2016

Sharks have a reputation for having voracious appetites, but a new study shows that most coral reef sharks eat prey that are smaller than a cheeseburger.

Vegans may lack essential nutrient intake, study reports

March 17, 2016

The health benefits of a plant-based diet is well-known, but the question remains: Could vegans be at risk for deficiency of essential nutrients? A retrospective review by Mayo Clinic physicians recently published in the ...

Recommended for you

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.