Adult male gopher tortoise
Photograph by Michael J. Connor
Introduction
The gopher tortoise (Gopherus polyphemus) saga begins with the evolution of sandhill ecosystems originating from marine sand deposits in the Plio-Pleistocene geological period from 5 to 15 million years ago. These coastal sands eventually mixed with soils to provide the growing base for arid-type plants that preferred sandy, well-drained soils. The primary plant community is composed of longleaf pine, turkey oaks, and wire grass. These plants are fire resistant, and in fact, the entire community is called a fire subclimax forest. Natural and man-induced burning on a regular cycle is essential to maintain the character of this habitat. Other prominent plants include lichens, yuccas, palmetto, shrubs, wildflowers, gopher apple and prickly pear cactus.
Perhaps the most important animal in this ecosystem is the gopher tortoise. Its presence is apparent from the burrows which it digs into sandy soils. Its burrow may be 10 feet deep and 25-35 feet (diagonally) long, providing a well insulated refuge for the tortoise as well as 358 other species including 301 invertebrates and 57 vertebrate species. The creation of the burrow refuge has acknowledged the gopher tortoise by ecologists as the keystone species for its habitat. Among the inquilines (co-inhabitants of the burrow) include the dung beetle which converts the dung into soil nutrients, the gopher frog which is found nowhere else but in burrows, various snakes such as the pine snake, coachwhip racer, red rat snake, gray rat snake, the eastern diamondback rattlesnake and the threatened Eastern indigo snake. Occupiers of abandoned burrows include the fox squirrel, opossum, raccoon, red and gray foxes, bobcats, armadillo and bobwhite quail. Based on this extensive inventory, the gopher tortoise deserves the title of keystone species.
Distribution
Gopher tortoises are found from southeastern South Carolina through southern Georgia and most of Florida (except the Everglades), westward through southern Alabama and Mississippi and the eastern "toe" of Louisiana. They also occur on coastal islands off Georgia and Florida. Most of its habitat is located on private lands with a very small percentage located on public, state, federal or military reserves.
Biology and Ecology
The best way to sex a gopher tortoise is to gently turn one on its back and inspect its plastron or ventral surface. For adults, if the plastron is flat, it is probably a female. A concave plastron indicates a male. Juveniles cannot be sexed except by an expert. The gopher tortoise exhibits deferred sexual maturity, low fecundity and a long life span. Adults require 16-21 years to mature and may live 40 years or longer. Mating occurs during April to June, with females digging their nest cavity in the mouth of the burrow only once per year. The extremely low reproductive rate is a major limiting factor. The mean clutch size is approximately 6 eggs. The incubation period varies latitudinally from about 80-110 days. Nests are very susceptible to predation.
Nest loss may reach 87% due to various predators including snakes and mammals. Based on burrow counts in northern Florida, it is estimated that from time of egg laying through the first year, the recruitment potential can be reduced by about 94%. Hatchlings will either dig their own miniature burrow or seek shelter opportunistically under sand, debris, or litter.
Gopher tortoise density and movements are affected by availability of forbs and grasses. Home range is inversely related to the amount of herbaceous grass cover. As the principal sandhill grazer, the gopher tortoise feeds primarily on grasses, succulent plants and legumes. Legumes appear to be particularly important in the diet of juveniles. The gopher tortoise serves as a seed dispersal agent for native grasses and returns leached nutrients to the surface during burrow construction.
Population Status
Formerly common, the gopher tortoise has now been extirpated from parts of its range and many remaining populations are declining. Habitat destruction, habitat degradation through fire exclusion, and human predation have reduced the original number of tortoises by an estimated 80% over the last 100 years. A particularly unethical practice of "gassing" tortoise burrows to remove rattlesnakes is still legally allowed in Georgia, taking an unknown toll of gopher tortoises and inquilines. This wanton practice can also lead to the destruction of the burrow and refuge for the inquilines. In South Carolina, disjunct populations (estimated 200-2,000 individuals) exist in three counties, primarily on private lands. In south Georgia, which possibly contains the largest populations next to Florida, the tortoise still occurs on sand ridges in at least 81 counties. Throughout the Georgia Coastal Plain, populations have been fragmented by urban and agricultural development and depleted by over-harvesting and habitat destruction. Vast tracts of gopher tortoise habitat are owned by politically powerful forest products industry and associated private pine plantation owners. In Florida, the gopher tortoise remains relatively widely distributed, occurring in all 67 counties (estimated population 1.2 million). However, on the average, 1,000 people take up residency in Florida weekly. Unregulated growth reigns supreme, particularly in the southern part of the state, which displaces gopher tortoises to peripheral habitat. Gopher tortoises are still common in northern and central parts of peninsular Florida, but peripheral populations in the west and south have disappeared or are declining rapidly. Urban displacement, phosphate mining, and citrus production have had an impact on populations in central Florida. Human predation has depleted populations in the Florida Panhandle, and west Florida tortoise hunters now travel to Georgia and other states to illegally collect specimens. Tortoises occur in at least 21 counties in southern Alabama. Populations in that state appear to be recovering from past exploitation, however, exclusion of fire from upland habitats and creating corridors for highways and gas pipelines remain a problem. Agricultural and forestry practices have had a severe impact on tortoise populations in their 14 county range in southern Mississippi. The largest remaining population occurs in the DeSoto National Forest where the U.S. Forest Service is making a conscientious effort to protect and manage the species. Gopher tortoises have apparently been a relictual species in Louisiana as in South Carolina. Pine plantations with emphasis on thickly planted stands of loblolly pine have contributed to the near extinction of tortoises in Louisiana (estimated native population of less than 100).
Threats to Survival
The most significant threat is loss of habitat to intensive land use, particularly housing projects, industrial centers, corporate agriculture and forestry, phosphate strip-mining and sand extraction. As stated earlier, most of the land is in private ownership, with only a small percentage in military, federal or state reserves.
Another factor of importance is the exclusion of fire from natural longleaf pine and scrub oak habitats, thanks to the "Smokey the Bear" syndrome. An open canopy and relatively litter-free ground are necessary for food production and nesting, and such conditions are favored by regular burning. Tortoise numbers may be reduced by as much as 60-80% when burning is excluded for 8 or more years. The use of heavy machinery to reduce logging debris in preparation for planting pine trees is detrimental to gopher tortoises. However, studies in southern Georgia and northern Florida demonstrated that gopher tortoises are able to dig out following chopping treatment on deep sandy soils.
