A frog tale a decade in the making
- Laurie D. Babcock
- June 25, 2024
- College of Arts and Sciences
- Contributors: James Greco, Photos | Laurie D. Babcock and Chris Noonan, Video
6 – minute read
It may come as no surprise that recent biology major Bryce Sweely’s favorite movie is “Jurassic Park.” In the 1993 film and the Michael Crichton book on which it’s based, scientists use frog DNA to fill in the dinosaurs’ genetic code. This introduces unexpected traits into the lab-grown dinosaurs, impacting the park’s ecosystem.
Sweely encountered similar issues at Florida Gulf Coast University, where she’s researched local frog species for the past two years. Invasive Cuban treefrogs pose challenges to the local FGCU ecosystem, outcompeting native species and altering food webs.
“Every species has its place,” Sweely says. “If one species is affected in some way or goes extinct, we could see ripples of that throughout the ecosystem. It’s important for us to conserve the natural spaces we have left.”
After two years of campus frog research, she was heading into a conservation area before her May graduation to take down the last of her research equipment. Accompanying her was assistant professor of wildlife biology and Sweely’s faculty adviser, Andrew Durso. His work focuses on amphibian and reptile ecology, and he’s overseen Sweely’s independent fieldwork since 2023.
“I’ve mostly worked on snakes — but snakes eat frogs and without frogs you won’t have certain snake species, so it’s all connected,” Durso says.
Wearing waders and boots, Sweely and Durso cross the campus loop road to one of FGCU’s nature trails. They travel deep into a cypress dome where Sweely had set up almost a dozen frog tubes. At the start of the project, she cut PVC pipes to varying lengths and secured them around tree trunks with bungee cord. Tiny frogs are attracted to the snug tubes, which may prevent them from drying out and protect them from predators. Sweely checked 90 tubes every two weeks for almost two years, tracking the numbers of invasive and native frog species at multiple campus sites.
On this final trip, the only frog Sweely finds is an invasive Cuban treefrog no bigger than a Matchbox toy car. Using a small sponge on a long stick, she gently coaxes the frog out of the tube into a plastic bag, measures it and notes the tube’s location. Before releasing the frog, she and Durso emphasize the importance of maintaining natural habitats for native species and preventing the spread of invasive species.
“Invasive species are like litter that makes copies of itself,” Durso says.
In the 1990s, on what would one day become the FGCU campus, Durso says there were four native treefrog species in the area — squirrel, green, pine woods and barking. By 2013, pine woods and barking treefrogs were no longer found on campus.
“We’ve already lost indigo snakes, gopher tortoises, pygmy rattlesnakes, pine woods treefrogs and barking treefrogs.” Durso says. “Bryce’s work shows we are in danger of losing green treefrogs. What next?”
Sweely’s research builds on the work of Logan McDonald (‘14, biology and environmental studies), who conducted similar research as an undergraduate. McDonald, now the community outreach coordinator for Pensacola & Perdido Bays Estuary Program, aimed to determine the population sizes of Cuban treefrogs and native frogs in developed campus areas.
McDonald’s research resurfaced when Sweely heard about it from Matthew Metcalf, a biologist and herpetologist, during a study abroad trip to Peru. Inspired by her Amazon experience, Sweely decided to continue McDonald’s research with Metcalf as her first faculty advisor through the Honors College.
Both student researchers expected to find more Cuban treefrogs than native frogs near campus buildings. They focused on five sites in North Lake Village and five in main campus conservation areas. Sweely closely replicated McDonald’s research design, providing an opportunity to evaluate changes in population status.
“We’ve seen a decline in native treefrogs as a whole, both squirrel and green, in urban areas. Based on some occupancy modeling — whether or not the frogs inhabit an area — native treefrogs are much less likely to be found in urban areas now than they were a decade ago,” Sweely says.
McDonald left detailed records that Sweely and Durso used to compare frog populations. Sweely calculated an “encounter probability,” comparing her findings with McDonald’s from 2013-14.
Squirrel treefrogs and green treefrogs were still common in campus conservation areas in 2013. In 2022-24, squirrel treefrogs remained common, but Sweely captured only a single green treefrog. Durso says this indicates the species’ sensitivity to campus development.
Ecologists rarely document and study population declines or local extinction events because they are hard to predict. Durso says the opportunity to compare over long time scales is rare.
“Ten years isn’t the longest-term ecological study — but anyone who lives in Southwest Florida can tell you how much change has taken place over the past 10 years,” Durso says.
“Being able to revisit a research project from a decade ago has made me more aware about how urban development may be affecting both our native and invasive species,” Sweely says. She hopes her follow-up study of McDonald’s research will help contribute to future conservation efforts and land management decisions. Her research will continue as she starts her master’s degree at FGCU in the fall.
“Every day brings a new opportunity to help protect the Gulf coast that I grew up on,” McDonald says. She and her husband have treefrog pipes in their Pensacola backyard. “Once a frog fanatic, always a frog fanatic.”
McDonald worked under John Herman, Durso’s late predecessor. “It’s an honor to continue their work,” Durso says. “Maybe in 10 years another student will extend the project into a third decade.”
