A map created by the Tennessee Aquarium and collaborators defines the boundaries of 16 biogeographical “provinces.” Each color represents a unique turtle community. Similar color shades represent broader level “super-groups” that have more in common than with other colors, e.g., red vs. green. (Map: Tennessee Aquarium)

In order to conserve a species, scientists must first know where that species resides and why.

Tennessee Aquarium Conservation Institute scientists Dr. Josh Ennen and Sarah Sweat have conducted a first-of-its-kind study that seeks to answer these fundamental questions in regards to North America’s many turtle species.

In collaboration with other North American experts, Ennen and Sweat worked to map the geographic boundaries of all turtle communities in North America—the “where?”—and analyze how modern and historical forces have shaped these patterns—the “why?”

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The resulting groundbreaking report was published in the latest issue of Herpetological Monographs.

Although many scientists research turtles at the level of individual species or single habitats, this study represents the first attempt to consider them on the scale of the entire continent. With this new map, North America is divided into 16 biogeographic “provinces,” sprawling regions containing turtle species with similar or shared characteristics. Looking at these turtles in such a broad context enabled researchers to determine that the provinces’ borders were defined by many forces, from modern environmental factors to ancient geologic processes.

“As scientists, we need to consider all of those factors to understand why turtles are threatened, in some cases,” Ennen said in a prepared statement. “We produced some useful maps, and I think there are numerous conservation implications for this study, eventually.”

A Barbour’s map turtle at the Tennessee Aquarium. (Photo: Casey Phillips, Tennessee Aquarium)

In some cases, researchers have determined that the modern distribution of turtles is a result of ancient geological events. As an example, the study found similar species to those living in the Mississippi River on the western side of Crowley’s Ridge—more than 40 miles to the west. According to Ennen, this similarity of otherwise-isolated populations can be explained as a kind of echo from when the Mississippi flowed along a more westward course.

“I thought that was pretty cool that you could still see that,” he said.

Biologists consider the southeastern U.S. a hotspot of biodiversity, especially of turtles. A 500-mile radius around Chattanooga contains fully half of North American turtle species.

The Tennessee Aquarium houses the world’s largest collection of freshwater turtles. Guests can see alligator snapping turtles and many map turtle species that reside in this area by visiting the Mississippi Delta Country Exhibit.

Nearly 60 percent of turtle species are threatened with extinction, making them the world’s most endangered group of vertebrates.

Ennen said that one of the keys to protecting them and offsetting their collective decline is by helping conservationists better understand where turtles live and the roles they play in their habitats.

Findings from this study, and future research that it paves the way for, will help scientists determine where to devote time and resources to protecting these biologically important, imperiled animals.

“Turtles are underappreciated, but they play pivotal roles in many ecosystems, from seed dispersal to altering the environment around them,” Ennen said. “If we lose turtles, we potentially lose a vital function in those ecosystems. We can’t afford that.”

A “heat map” indicating turtle species richness across the globe. Warmer colors indicate more species in a given location. (Map: Tennessee Aquarium)
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