An up close shot of a midden, or ancient packrat nest, from the collection being studied by KU researchers. Individual leaves, seeds and other material that make up the nest is visible.

Packrats — pests or preservationists?

That depends.

Modern packrats have a reputation for ruining car engines and invading attics with nests they cram with debris. But Kansas University researchers have found nests of their ancient kin to be a powerful tool for studying climate change’s effect on plants.

“These rodents, or packrats, are the original hoarders,” postdoctoral researcher Katie Becklin said. “They create their nests using many different items such as sticks, leaves, seeds, thorns and bones from their local environment. Plant tissue is well-preserved in these middens, and we can use measurements of stable isotope ratios to better understand how these ancient plants functioned when they were alive.”

Becklin collaborated on the project with Joy Ward, plant biologist and associate professor of ecology and evolutionary biology at KU, and two other researchers. The scientific journal Ecology Letters published their findings this spring, but Becklin said they are continuing research on the topic.

The study explores how plants survived in North America 21,000 years ago — the last glacial period, when temperatures and carbon dioxide concentration in the atmosphere were significantly lower. It relies on samples from a community of ancient conifer plants preserved within nests, or middens, of packrats that lived in Nevada’s Snake Range during that time period.

The middens were gathered by the late Phillip Wells, a former faculty member in KU’s Department of Ecology and Evolutionary Biology. He collected pieces of nearly 400 nests ranging from 2,000 to 50,000 years old, and KU says it’s one of the finest collections of glacial plants in the world.

The nests in nature get very large, as generation after generation of packrats adds onto them, Becklin said. The pieces her team worked with range from the size of a baseball to a small table.

These samples exist thanks to packrats’ longstanding practice of urinating in the same place they sleep.

The middens are not fossilized. Rather, Becklin said, the rats’ urine crystallizes and forms a hard coating that preserves pieces of plant material.

“They look like a pine needle that had just fallen off a tree yesterday,” Becklin said.

Becklin said her team’s results suggested that most plant species they found in the middens altered their physiologies in response to environmental changes. Those past responses could yield information about how plants might continue to adapt.

“Having this past perspective on what happened is really important for figuring out how we can best predict what’s going to happen in the future,” she said.