UNC biologist Eric Riddell (pictured in the North Carolina Botanical Garden in Chapel Hill) uses ecophysiology to understand how animals respond to environmental changes due to rising temperatures. (photo by Donn Young)
After a long day of fieldwork in the Galápagos, the only thing on Eric Riddell’s mind was water, food, a change of clothes and rest — he had spent the day banding Nazca boobies and was drenched in sweat and bird poop.
Unbeknownst to Riddell, a surprise was waiting for him. Upon returning to his beach campsite, he found a sea lion snoozing in his bed.
In 2010, Riddell had journeyed to the Galápagos after graduating from Sewanee: The University of the South with an undergraduate degree in biology. Before that, he was living at home and working at a furniture store.
“You know, really putting my biology degree to work,” he said, joking. His plans included applying to dental school, but Riddell acknowledged he was not excited about his future career.
“There wasn’t enough uncertainty in my day-to-day,” he said. “I wanted more adventure and question marks and flexibility.”
The Galápagos Islands offered all that and more.
Riddell ended up on the main island, Santa Cruz, doing a number of different jobs but was on the hunt for biology work. He saw a posting for a fieldwork position, and even though he was underqualified, Riddell was hired on the spot, leading to work with the distinctive booby bird.
Doing the dirty work
Riddell spent the next eight weeks on the uninhabited island of Española, home to a colony of 10,000 Nazca boobies. Every day, he and his colleague would get up before dawn and trek across the rocky terrain to the birds’ nesting site. When adults returned from foraging in the ocean, the duo would note their leg bands and attach a corresponding band to their chicks. They also identified what the birds were eating.
The experience was a turning point in Riddell’s career.
The survey had been conducted for decades, and over the years researchers discovered that the birds’ prey had changed. In the ’70s and ’80s, it was small nutrient-rich fish like sardines and anchovies. But because the Humboldt Current had shifted over the last few decades — swinging wider off the Galápagos and taking cold, nutrient-rich water further out to sea — they were eating other fish, like mackerel and flying fish.
“It was so cool linking these global patterns like ocean currents to how this organism functions,” Riddell said. “Basically, I came home and was like, ‘I’m going to try to become a professor and do science.’”
Riddell went on to graduate school at Clemson University, did postdoctoral work at the University of California at Berkeley, then joined the department of ecology, evolution and organismal biology at Iowa State University. He came to UNC in 2023 as an assistant professor in the department of biology, where he conducts experiments and modeling to examine how climate change drives species’ distribution, adaptation and extinction.
Heat and habitats
The Earth’s surface temperature today is 2.7 degrees Fahrenheit hotter than it was in the pre-industrial era. That number has significant impacts — causing temperature extremes, melting sea ice and intensifying rainfall events, just to name a few examples. It is also changing habitat ranges for plants and animals — expanding some and shrinking others.
The effects of climate change aren’t felt equally across species, and Riddell’s work explores this nuance, specifically examining how heat interacts with an organism’s physiology.
“I study ecophysiology, meaning how an organism functions in the context of their environment,” he said. “The two are inextricably linked — the second you remove an organism from its environment, it kind of loses a part of itself.”
Using heat and water loss as a lens, Riddell explores how organisms expend energy — how much they burn on a day-to-day basis, how much is assimilated into their body and how they allocate that energy toward tasks like growth, reproduction and defending their territory. Going a step further, he also examines how behavior and traits at the individual level influence genetic evolution.
“I think about an animal’s energy and mass budget,” he said. “They are eating food and burning energy; they’re drinking water and losing water. I’m basically an accountant for all of that — energy in and energy out — and I try to determine where in the environment the organism can have sufficient energy to survive.”
Riddell answers these questions through non-invasive lab experiments and computer modeling.
Experiments involve using a flow-through respirometry chamber — a small glass enclosure that passes air over the animal and analyzes gases under ecologically relevant conditions. This tool gives insight into water loss rates, metabolic rates, oxygen consumption, carbon dioxide production and the breakdown of carbohydrates, lipids and proteins. All this translates to how much energy the animal is storing and burning.
Armed with this data, Riddell and his team can then plug relevant information into computer simulations mimicking a variety of environmental conditions, like increased temperatures.
“Using this physical framework, we can predict things like animals’ physiology, how much energy they’re burning, where they’re active, when they breed or how dehydrated they become,” he said. “This one window — looking at body temperature — opens a world of understanding.”
Small, but mighty
As darkness falls on the Blue Ridge Mountains, there’s a change of the guard. Chirps from songbirds are exchanged for the squeaks of bats. Hawk calls go quiet, and owls take their place. The buzz of insects disappears from the soundscape, and frogs fill the void.
On the forest floor, much quieter animals emerge — an army of salamanders.
North Carolina boasts the highest concentration of salamander species on the planet. These amphibians need a cool, wet environment, so the Blue Ridge Mountains’ temperate rainforests are a perfect place to call home.
That’s also why UNC, with its partnership with the Highlands Biological Station through the Institute for the Environment, is the perfect place for Riddell. Much of his work explores the evolution, adaptation and behavior of this animal family.
Knowing how salamanders will fare in the future is also important for understanding the outlook for their broader environment. As voracious predators, they play an important role in pest control. They also help sequester carbon.
One lab project, in collaboration with Martha Muñoz at Yale University, explores salamander diversity.
Some species can only be differentiated by sequencing their genes — they look identical and can even breed together. Riddell’s team sought to understand what was happening with the species’ physiological diversity.
The team collected hundreds of salamanders across 35 species to measure these traits. They then analyzed results and plotted species on a phylogeny — think of it as a family tree of the evolutionary history between species.
“We wanted to know to what extent evolution and natural selection are shaping these patterns of diversity,” Riddell said. “And we found that the species are actually really different. There are clear signatures of certain groups of species that may be selecting certain environments in the Appalachian Mountains and evolving in ways we hadn’t appreciated before.”
The data was then used in climate simulations to map where species could and could not survive in future climate scenarios.
This recipe for studying climate vulnerability can be applied to a variety of scenarios and species, Riddell said. A project his lab has with the San Diego Zoo is determining where desert tortoises will survive in worst-case climate scenarios and translocating populations. Another with Molly Womack at Cornell University explores how frogs’ skin evolves and adapts to different environments.
Riddell’s work is an example of why fundamental research is important to fueling future solutions to complex problems. He wants to help inform decision makers on where conservation efforts will make the most sense.
“I’m always thinking broadly, thinking deeply,” he said. “Thinking in ways that change how we fundamentally think about life.”
By Megan May
The UNC campus celebrates University Research Week Oct. 21-25 with the theme “Back to Basics,” highlighting the power of foundational research at Carolina and its real-world impact across disciplines. Enjoy more research stories throughout the magazine.
Published in the Fall 2024 issue | Features
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