A Keystone Species
The gopher tortoise’s burrows provide refuge for other animals in peril
The gopher tortoise (Gopherus polyphemus) is one of four terrestrial tortoises found in North America, and the only one east of the Mississippi River. Its range covers Alabama, Mississippi, Louisiana, South Carolina, Georgia and Florida. In the eastern portion of its range it is state listed as threatened in Florida, eastern Alabama, Georgia and South Carolina. In the western part of its range it is federally listed. Because of its population decline in its eastern range, it is also under review to be federally listed as a threatened species. In Florida it is protected by permitting through the Florida Fish and Wildlife Conservation Commission.
The gopher tortoise has a rounded, oblong carapace that is gray or tan, and it can reach 15 inches and weigh 24 pounds. Its hind feet are rounded and elephant like, while its front feet are spade-like with toenails that are short and broad.
The gopher tortoise lives in a burrow that it digs with its specialized front legs in dry habitat such as oak hammocks, xeric scrub, longleaf pine-turkey oak, beach scrub, pine flatwoods and palmetto prairie. The burrow may run underground 30 feet or longer at depths of 18 feet. The gopher tortoise digs down to moist clay where the burrow ends in a den. The burrow is just a little wider than the length of the tortoise, enabling the tortoise to turn around.
These burrows are important to more than 300 species of invertebrates and approximately 57 vertebrate species. Because so many commensal species depend on these burrows to survive, the gopher tortoise is considered a keystone species. Its burrow provides protection from predators, extreme heat, cold, fire and drought. The gopher tortoise spends approximately 80 percent of its time in the burrow or nearby foraging on nonwoody plants and grasses or basking in the sun. It lays an average of six (ranging from three to 12) spherical, white, hard-shelled eggs at the mouth of the burrow. Incubation lasts 80 to 110 days.
On average the gopher tortoise lives to an age of 60 years. A few may live as long as 80 to 100 years. Depending on the individual, a female can start reproducing at 9 to 21 years of age. The male is sexually mature at a younger age. The gopher tortoise nests only once a year from May to July. Both its eggs
THESE BURROWS ARE IMPORTANT TO MORE THAN 300 SPECIES OF INVERTEBRATES AND APPROXIMATELY 57 VERTEBRATE SPECIES.
and hatchlings are preyed upon by raccoons (Procyon lotor), skunks (Spilogale putorius and Mephitis mephitis) and a variety of snakes. Mortality of eggs and hatchlings together can reach 92 percent. It is estimated that most females have a successful nest only once in 10 years. The few gopher tortoises that make it through the first five to seven years of the hatchling and juvenile stages grow big enough and develop a hardened shell to increase their chance of survival, as long as they have optimum habitat. Optimum habitat can support approximately four tortoises per acre, while less favorable habitat may support only one
per acre. Adults are also susceptible to highly contagious upper respiratory tract disease, which can be fatal to some infected individuals.
Current tortoise population densities are estimated to be less than 20 percent of their historic numbers. Habitat loss and fragmentation is the primary threat to the species. Tortoise habitat is being lost to development or from lack of habitat management practices such as prescribed burning. Without perpetual management, habitat evolves to a closed canopy with limited herbaceous vegetation. Exotic and invasive vegetation also replaces native plants. Eradicating Brazilian pepper (Schinus terebinthifolius), melaleuca (Melaleuca quinquenervia) and cogongrass (Imperata cylindrica) is important. As the habitat degrades, tortoises are excluded.
Gopher tortoises require at least 30 percent open upland habitat. Favorable habitat should include treeless open areas to scattered areas of 30-40 percent tree canopy. Some mechanical tree and shrub clearing may be necessary, but optimum management should include prescribed burning every two to five years and annual treatment of invasive or exotic vegetation. This would provide adequate forage for the gopher tortoise including wiregrass (Aristida beyrichiana), butterfly pea (Clitoria mariana), sensitive briar (Schrankia microphylla) and gopher apple (Likania michauxii).
As mentioned, the gopher tortoise is a keystone species notably because its burrows provide refuge for many animal species. These include the threatened eastern indigo snake
(Drymarchon corais couperi), the species-of-special-concern gopher frog (Rana capito) and invertebrate species found only in tortoise burrows. The loss of gopher tortoises and their burrows would have a negative impact on the biodiversity and ecology of the southeastern United States.