A Thousand Invisible Cords

Whitham - Interior - Cottonwood tree
Cottonwood tree, 18 months after planting

Thirty years ago, NAU Regents’ Professor Tom Whitham (Department of Biological Sciences) and students began an experiment that would eventually change how we view the world. No longer would we see species as isolated members of ecosystems but as genetically connected members of a rich community of interacting species. This groundbreaking research, which merges different disciplines, such as ecology and genetics, would demonstrate that the world is bound together in more ways than most people thought possible—findings that could help solve global problems our planet is facing: from responding to climate change to guiding restoration of damaged ecosystems and even gauging the effects of new technologies on the environment.

Genetics of foundation species “drive” whole ecosystems

The science, which is explored in the new documentary A Thousand Invisible Cords (produced by NAU's IDEA Lab), began with the study of one tiny insect—an aphid.  Aphids feed on cottonwoods—a fast-growing tree native to the banks of North American waterways. Whitham wanted to learn how a cottonwood’s genes affect its susceptibility to aphid attack. 

He noticed that some trees were heavily attacked, while other adjacent trees were hardly touched. He wondered whether the differences were genetically based or a result of environmental conditions, such as differences in the soils in which the trees grew. So Whitham took cuttings from 81 cottonwoods growing along Utah’s Weber River and planted them in a common garden at the Ogden Nature Center, a 152-acre nature preserve and education center in Utah. The environmental conditions were held constant so that any differences observed in the patterns of aphid survival on the cottonwoods had to be caused by genetic differences among trees. The experiments clearly confirmed the genetic hypothesis.

Subsequent research showed that genetically different cottonwoods affect far more than just the aphids, they affect a rich community of about 700 insect species, the microbial community in the soil, lichens on the trunk, fungi that live in the twigs, the birds that feed on the insects, and the beavers that selectively fell trees with specific traits. Thus, a whole community was largely defined by the underlying genetics of the cottonwood trees. Because cottonwoods and their interactions with a few other species structure the community by creating a stable habitat for other species, they are considered “foundation” species.

A small change in just a few lines of a foundation species’ genetic code can have cascading effects on whole communities and even ecosystem processes. These findings provide an unparalleled opportunity for molecular geneticists, ecologists, and restoration biologists to work together as never before to solve important environmental problems facing our world.

A shortcut to unraveling complex problems

With decades of data and hundreds of publications behind them, members of the Cottonwood Ecology Group continue to make new and exciting discoveries. They have also built key partnerships with land-management agencies so that basic research, conservation, and restoration can be conducted simultaneously. 

“This genes-to-ecosystems approach offers a simplified way of going after very complex problems because we’re concentrating on the genetics of the relatively few foundation species and their interactions that drive the rest of the community—rather than trying to study the genetics of every organism simultaneously,” says Whitham.

“Sometimes there is a perception that curiosity about the working of seemingly trivial organisms such as an aphid is ivory tower research of no consequence.  Yet, such research often results in the discovery of fundamental principles. In turn, these principles result in major applications to address some of the most pressing biological issues of our time that do address the world we live in, our own quality of life, and the human condition.”

Whitham - Interior 2 - Cottonwood trees
A gallery forest in 13 years at a former Super Fund Site. In the lower-right, a human is used to demonstrate scale.

For example, the knowledge gained in these and other studies have allowed researchers to identify trees that support the greatest biodiversity and that are drought tolerant, fast growing, genetically resistant to insect attack, and best for restoration.

Whitham honored with Eminent Ecologist Award

Whitham’s research has not gone unrecognized. Whitham and other members of the Cottonwood Ecology Group have been consulted by the European Union and the U.S. Department of Interior and Animal Plant Health Inspection Service (APHIS).  In 2011 Whitham received the prestigious Eminent Ecologist Award by the Ecological Society of America—the group’s highest honor—for his outstanding body of work. He was also elected a Fellow of the American Association for the Advancement of Science.  In addition to being an NAU regents’ professor, Whitham is Executive Director of the Merriam-Powell Center for Environmental Research.