Betsy Roznik, M.S. (Dec. 2007)
Betsy received a Master of Science degree in December 2007 from the
Department of Wildlife Ecology and Conservation at the University of
Florida, where she used radiotelemetry to study patterns of movement,
habitat use, and survival of juvenile and adult Gopher Frogs (Rana
capito). Gopher Frogs breed in ephemeral ponds, but they spend the
majority of their lives in the surrounding terrestrial habitat, where
they take shelter in underground refuges such as the burrows of Gopher
Tortoises (Gopherus polyphemus) and small mammals. Habitat loss and
degradation have caused Gopher Frog populations to decline, including
the suppression of natural fire regimes. By studying the habits of
these frogs, Betsy hoped to gain important information that could be
used to make recommendations for habitat management.
Betsy found that both juvenile and adult Gopher Frogs preferred open-canopy longleaf pine (Pinus palustris) savannas that had been maintained by prescribed fire, and avoided shady habitat that had been invaded by hardwoods as a result of fire suppression. She also found that fire-maintained habitat has a higher density of burrows than fire-suppressed habitat, which means that it has more possible shelter sites for Gopher Frogs. Betsy found that burrows were essential to the survival of juveniles; frogs that spent time aboveground were very likely to be eaten by snakes and other predators. Betsy's findings emphasize the importance of frequently burning terrestrial habitat near ponds in order to maintain suitable habitat for Gopher Frogs and the burrowing animals they depend on for shelter.
Betsy’s ongoing research focuses on the ecology, behavior, conservation, and management of amphibians and reptiles. She is currently a doctoral candidate at James Cook University (Australia), where she is studying the behavior of rainforest stream frogs and how intraspecific variation in behavior affects their susceptibility to chytridiomycosis, the disease caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis). Click here to go to Betsy's webpage at James Cook University.
- Roznik, E.A., and S.A. Johnson. 2007. Rana capito (Gopher frog). Refuge during fire (134KB pdf). Herpetological Review 38:442.
- Roznik, E.A., S.A. Johnson, C.H. Greenberg, and G.W. Tanner. 2009. Terrestrial movements and habitat use of gopher frogs in longleaf pine forests: a comparative study of juveniles and adults (380KB pdf). Forest Ecology and Management 259:187-194.
- Roznik, E. and S.A. Johnson. 2009. Burrow use and survival of juvenile Gopher Frogs (Rana capito) (176KB pdf). Journal of Herpetology 43:431-437.
- Roznik, E. and S.A. Johnson. 2009. Canopy closure and emigration by juvenile Gopher Frogs (343KB pdf). Journal of Wildlife Management 73:260-268.
- Roznik, E.A. and S.A. Johnson. 2009. Rana capito (Gopher frog). Burrow cohabitation. Herpetological Review 40:209.
- Johnson, S.A., E.A. Roznik, G.W. Tanner, and C.H. Greenberg. 2008. Habitat use by Florida gopher frogs in savanna-like versus hardwood-invaded longleaf pine-wiregrass uplands. Final Report. Florida Fish and Wildlife Conservation Commission, Tallahassee.
- Roznik, E.A., and S.A. Johnson. 2009. Gopher Frogs, Burrows and Fire: Interactions in the Longleaf Pine Ecosystem. Florida Cooperative Extension Service Publication WEC 250, Institute of Food and Agricultural Sciences, University of Florida, Gainesville.
Thesis Abstract (Full-text link below abstract)
TERRESTRIAL ECOLOGY OF JUVENILE AND ADULT GOPHER FROGS (Rana capito)
Although many amphibians that breed in aquatic habitats spend the majority of their lives in surrounding upland habitats, the terrestrial ecology of amphibians is poorly understood. I used radio telemetry to study survival, movement patterns, and terrestrial habitat use of juvenile and adult gopher frogs (Rana capito). Both juvenile and adult frogs are capable of migrating long distances from breeding ponds. In my study, juveniles moved at least 691 m from ponds, and adults moved at least 396 m from ponds; however, other adult gopher frogs were observed up to 862 m from the nearest potential breeding pond at my sites. The final recorded locations of all surviving frogs that migrated from ponds were burrows excavated by gopher tortoises (Gopherus
polyphemus) and small mammals (e.g., Geomys pinetis, Podomys floridanus), and both life stages exhibited strong site fidelity to these burrows.
Predation on juvenile gopher frogs was extremely high and only 9.4% of frogs survived their first month in the terrestrial environment. Although snakes were their major predators, frogs were also killed by mammals and birds, as well as vehicular traffic along unpaved roads. The use of underground refugia significantly increased a frog’s probability of survival and reduced the risk of death to only 4% of the risk that frogs faced while in the open environment. Frogs that survived to the end of the study located a burrow within their initial days in the terrestrial environment and remained there for the rest of the life of their transmitter.
Although my study ponds were located primarily in open-canopy longleaf pine (Pinus palustris) habitat, areas surrounding some of the ponds contained patches of closed-canopy habitat that had been invaded by hardwood trees (e.g., Quercus spp.) as a result of fire suppression. Emigrating frogs migrated nonrandomly at these ponds, moving through the center of the largest patch of open-canopy habitat, and thereby avoiding the edges where the closed canopy habitat occurred. Patches of open-canopy habitat contained higher densities of burrows than closed-canopy patches, suggesting that frogs select open-canopy habitats because burrows are more abundant in those areas.
Conservation of gopher frogs requires protection of large areas of terrestrial habitats surrounding breeding ponds, as well as protection of populations of burrowing vertebrates. Terrestrial habitats must be managed appropriately, which includes using frequent prescribed fire in the uplands and burning all the way to the edges of ponds.
- Roznik, E. A. 2007. Terrestrial ecology of juvenile and adult gopher frogs (Rana capito). M.S. thesis, University of Florida, Gainesville.