Gopherus polyphemus

Geographic Range

Gopherus polyphemus is found only in the southeastern United States. Its range extends through the Coastal Plain, from the southern tip of South Carolina through a small area at the extreme eastern end of Louisiana (Diemer 1986). The majority of the range of G. polyphemus is located in Florida. Small portions of southern Alabama, Mississippi, and Georgia are also part of the range (Conant and Collins 1998).

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Gopher tortoises are terrestrial tortoises and can be found in habitats with dry, sandy soils, a thin tree canopy, and plenty of low growing vegetation. Some common Gopher tortoise habitats include scrub, coastal dunes, sandhill, pine and scrubby flatwoods, prairie, pine-mixed hardwoods, and xeric hammock. Periodic burning is an essential component of Gopher tortoise habitat, as it inhibits the growth of tall, dense vegetation that prevents the growth of low growing plants that make up the tortoises’ diet. Within these habitats, G. polyphemus builds underground burrows. These burrows average 4.5 meters in length and 2 meters deep. These burrows, which maintain a steady temperature and humidity throughout the year, provide gopher tortoise with protection from fires, extreme temperatures, drought, and predators.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• desert or dune desert or dune
• savanna or grassland savanna or grassland
• forest forest
• scrub forest scrub forest

• Other Habitat Features
• suburban suburban

Physical Description

Gopher tortoises are moderately sized tortoises, averaging between 23 and 28 cm in carapace length as an adult, with a maximum length of about 38.7 cm. The average mass is 5500 grams (AnAge entry for ≪Gopherus polyphemus≫ 2012). They are easily identified by their unwebbed, flattened and stump-like hind feet, and forelimbs that are shovel-like and adapted for digging. The carapace of ≪G. polyphemus≫ is oblong and usually brown, tan, or gray in color (Gopher Tortoise Management Plan 2012). The plastron, which is unhinged, is a dull yellow and pale brown color. The carapace of younger tortoises has visible growth rings, which can be used to estimate age. In older individuals, the carapace is worn quite smooth. Hatchling gopher tortoises have yellow-centered carapace scutes, which are bordered by brown. The plastron and marginal scutes are yellow or orange (Conant and Collins 1998).

At sexual maturity, males and females are of similar size and appearance, though the female's shell dimensions may average somewhat larger. To differentiate between sexes, the most reliable characteristic is the concavity of the male's plastron; the female plastron is flatter. Males also have larger mental glands (on the chin) and longer gular projections on the front of the plastron (Mushinsky et al. 1994).

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike
• female larger
• sexes shaped differently

Development

Gopher tortoise eggs are fertilized internally and a single clutch is laid by a female each season. On average, a clutch has six eggs, though clutch size ranges from five to nine eggs. Incubation period ranges from 80 to 100 days, and depends on the latitude (and temperature trends) at which a nest is located. Nests located further south tend to have shorter incubation periods (Gopher Tortoise Management Plan, 2012). Gopher tortoises exhibit temperature dependent sex determination and have an unusually low pivotal temperature of about 29 degrees C (Burke et al. 1996). Nest and hatchling predation is very high. Those juvenile gopher tortoises that survive reach sexual maturity slowly, with female gopher tortoises reaching sexual maturity between 9 and 21 years. Male gopher tortoises may reach sexual maturity slightly earlier than females (Gopher Tortoise Management Plan, 2012).

• Development - Life Cycle
• temperature sex determination

Reproduction

Very little is known about how gopher tortoises find mates in the wild. Auffenberg (1966) described a courtship ritual used to attract mates in G. polyphemus . The ritual begins with the male walking in circles and bobbing his head. The female tortoise will approach the male, which results in the male bobbing his head more vigorously. Once the female has approached, the male will bite at her legs and shell, and particularly the gular projection. The female will walk backwards in a semi-circle and stretch her hind legs. This is followed by the male’s first attempt at mounting, which is usually unsuccessful and followed by more biting. The female begins to walk in a progressively tighter semi-circle. The male will then successfully mount the female and copulation follows. Odors from mental gland secretions may also stimulate mating readiness.

There is little evidence to suggest male gopher tortoises directly defend their mates. Rather, individuals do defend territories, which often overlap both within and between sexes. Some forms of territorial defense, which are seen more often in the breeding season, include ramming and charging. Territory defense may play a role in mate defense (Innes 2009).

In general, G. polyphemus can be considered a promiscuous breeder, which means both males and females mate with multiple partners. Promiscuity seems to be more prevalent when females are smaller. Evidence shows that larger females tend to have clutches fertilized by a single male; smaller females are more likely to have clutches fertilized by multiple males. For this reason, it may be appropriate to consider populations with larger females to be polygynous breeders rather than promiscuous (Moon et al. 2006).

• Mating System
• polygynous polygynous
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Breeding occurs from March through December (Gopher Tortoise Management Plan 2012). Females typically begin reproducing between ages 9 and 21. Males usually begin reproducing between ages 9 and 18. A female can produce one clutch per year, though an individual may not necessarily lay a clutch each year. Average clutch size is 6 eggs, but clutch size ranges from 5 to 8 eggs. Once a clutch is laid, no further parental care is given from either the female or male. Depending on the latitude at which a nest is located, it takes 80 to 100 days for hatching to occur. As noted previously, hatching occurs in less time in warmer habitats (Innes 2009).

Gopher tortoises have temperature dependent sex determination. At average incubation temperatures of 26 degrees C, 100% males are produced; at 29 degrees C, 75% will be males, and only females are produced at 32 degrees C. After hatching, the neonates take approximately 2 days to absorb the yolk sac. When they begin to forage, they are classified as hatchlings. Once the tortoises are subadults, the shell becomes hardened. Adults are considered sexually mature when they can easily be classified as male and female and demonstrate defensive and mating behaviors (Innes 2009).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous
• sperm-storing sperm-storing

Gopher tortoises exhibit no parental care other than a careful excavation and covering of the nest. After mating, a female gopher tortoise will dig a nest in which to lay her eggs. The nest may be located in close proximity to her burrow (often in the "apron" of cleared sand around the burrow entrance), unless the habitat is not an adequate nesting site (Innes 2009). After laying and covering the eggs, there is no evidence suggesting any parental care. Within a few weeks of eggs being laid, up to 87% of nests may be predated upon, according to one study. It is estimated that a female gopher tortoise may only have a successful clutch of eggs every ten years (Diemer 1986).

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female

Lifespan/Longevity

In the wild, gopher tortoises have an expected lifespan of 50 to 70 years. However, they can be difficult to age as their carapaces become smoother and growth rings are no longer visible due to wear. Captive gopher tortoises may live to at least 86 years of age (Innes 2009).

Behavior

Gopher tortoises are ectotherms, dependent on the sun for obtaining warmth needed for daily and seasonal activity. These tortoises are active throughout the year with peak activity levels from April to June and September to October. Gopher tortoises are most active during the day, making them diurnal (Innes 2009). They become dormant in winter, when temperatures are insufficient for normal activity for many weeks. Gopher tortoises can spend up to 80% of their time inside a burrow. Under appropriate environmental conditions they leave the burrow to bask and forage. Typically, temperatures below 21 °C and above 32 °C will cause them to remain in burrow.s Similarly, very high or low humidity may limit the activity level of gopher tortoises (Innes 2009).

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• crepuscular crepuscular
• motile motile
• sedentary sedentary
• solitary solitary
• territorial territorial

Home Range

Home ranges of gopher tortoises can vary in size from as little as 0.1 acres up to 8 acres (Innes 2009). The size of home ranges is determined by sex, habitat type, forage quantity and quality, and season, though there is also variation between individuals. On average, male home ranges are between 1.2 and 4.7 acres. Female home ranges, on average, are between 0.2 and 1.6 acres. Within these territories, individual gopher tortoises will often have multiple burrows (Gopher Tortoise Management Plan 2012). Home ranges are considered well defined, though the edges of individuals’ homes ranges tend to overlap. Older and larger tortoises tend to have larger territories than younger, smaller ones. Territories of females are frequently smaller than those of males, who tend to travel farther, presumably in search of potential mates. Increased habitat quality tends to result in predictably smaller home ranges, as individuals do not need to travel as far to find suitable food (Innes 2009).

Communication and Perception

There is little information available on communication and perception in gopher tortoises. As solitary animals, gopher tortoises appear to communicate very little with other individuals except during mating activity (Innes 2009). During mating rituals, males and females communicate visually (such as head bobbing by the male) and through touch, including biting (Auffenberg 1966), and quite possibly also through odor (pheromones). Both sexes have enlarged mental (chin) glands (larger in males, and swollen during the breeding season) and an enlarged scale on each forefoot. The tortoise may rub this scale on the chin gland and present it towards a potential mate. The communication use of vocalizations or subaudible sounds in this species may occur, but is presently poorly understood.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

Gopher tortoises are primarily herbivorous and has been known to feed on up to 400 different plant species. Many of these species are herbaceous, low growing plants including wire grass, blackberries, prickly pear cactus, legumes, and paw paw (Gopher Tortoise Management Plan 2012). These plants provide some of the water that gopher tortoises require; however, they will also drink water when available (Innes 2009). Approximately 70 to 80 percent of a gopher tortoise’s diet comes from grasses. However, other plant parts, including shoots, stems, fruits, flowers, leaves, and pine needles are also eaten. A very small portion of the tortoises’ diet is composed of fungi, lichens, carrion, bone, insects, and feces. These food sources seem to be more commonly eaten by females before and after nesting time (Innes 2009).

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Animal Foods
• carrion carrion
• insects
• terrestrial worms

• Plant Foods
• leaves
• roots and tubers
• wood, bark, or stems
• fruit
• flowers
• bryophytes
• lichens

• Other Foods
• fungus
• dung

Predation

Gopher tortoises are killed and eaten by a large number of predators; eggs and hatchlings are the most vulnerable life stages, but larger tortoises are not invulnerable to predation. Predators on eggs and young include, but are not limited to, raccoons, coyotes, bobcats, wild boar, skunks, hawks, bald eagles, and a number of snake species. Fire ants destroy many eggs and young tortoises. Adult gopher tortoises are less vulnerable to predation; however, they are sometimes killed by coyotes, bobcats, and domestic cats and dogs (Innes 2009). Humans, especially in the panhandle of Florida, are known to kill Gopher tortoises, largely for food; though this practice is not as common as it was prior to the 1980's, it still occurs in some rural areas (Gopher Tortoise Management Plan 2012). The best strategy gopher tortoises have against predation is remaining underground in a burrow, where larger animals cannot reach them. However, nine-banded armadillos may sometimes indirectly cause mortality by trapping them in caved-in burrows as they dig their own dens (Innes 2009).

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Gopher tortoises are vital to their communities and are considered a keystone species. Over 350 species, including 60 vertebrates and 302 invertebrates, have been shown to use gopher tortoise burrows. Gopher tortoise burrows provide a stable, protective habitat for these symbiotic species, many of which are considered to be mutualists (Gopher Tortoise Management Plan 2012). Population sizes of some mutualist species are directly correlated with the size of gopher tortoise populations. For example, the decline of the gopher tortoises led to the decline of eastern indigo snakes, ≪Drymarchon couperi≫, which is listed as Threatened under the U.S. Endangered Species Act. Additionally, some of the species that benefit from gopher tortoise burrows also benefit the gopher tortoises. Little gopher tortoise scarab beetles, ≪Alloblackburneus troglodytes≫, live in gopher tortoise burrows and eat tortoise feces (Gopher Tortoise Management Plan 2012). Gopher tortoise presence allows for higher biodiversity. The 362 species associated with gopher tortoise burrows includes mice, rabbits, opossums, snakes, frogs, burrowing owls, and insects (Gopher Tortoise Management Plan 2012).

• Ecosystem Impact
• disperses seeds
• creates habitat
• soil aeration soil aeration
• keystone species keystone species

Economic Importance for Humans: Positive

Gopher tortoises help maintain diverse natural communities. Most people enjoy seeing tortoises, and they may be considered a tourist attraction. They were sometimes collected for the pet trade, though in Florida it is now illegal to possess or sell a gopher tortoise without a proper license. In the past, in northern Florida, rural communities captured gopher tortoises and used them as a source of food (Gopher Tortoise Management Plan 2012; Innes 2009).

• Positive Impacts
• pet trade pet trade
• food food
• ecotourism ecotourism

Economic Importance for Humans: Negative

Gopher tortoises are found in habitats often desired for development. Due to their protected status, land developers are required to obtain permits before developing land where gopher tortoises are present. Sometimes, gopher tortoises may be relocated. At other times, however, the land is protected from development. A delay in development, or lack of development in protected habitats, may thus have a small negative economic impact on humans (Gopher Tortoise Management Plan 2012).

Conservation Status

Gopher tortoises are listed as "Vulnerable" by the IUCN Redlist and "Threatened" by the US Fish and Wildlife Service. They receive varying levels of protection from states where they occur. The leading cause of decreasing numbers of gopher tortoises is habitat loss and degradation. Habitat degradation and fragmentation are due to practices such as urbanization, agriculture, and the mining of phosphates. Many tortoises are killed on roads. To help protect the species, some critical habitat is being managed and protected by state wildlife agencies from development and destruction (Gopher Tortoise Management Plan 2012).

Other Comments

Fossils of gopher tortoises are known from Pliocene and Pleistocene deposits throughout the present range of the species, but fossils that likely belong to this species have been found in Texas and Kansas, suggesting a larger range in the past.

Additional Links

Encyclopedia of Life

Contributors

Andrea Lazzari (author), Michigan State University, James Harding (editor), Michigan State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Auffenberg, W., R. Franz. 1978. Gopherus polyphemus . Cat. Am. Amphib. Rept. , 215: "1-2".

Auffenberg, W. 1966. On the Courtship of Gopherus polyphemus. Herpetologica , 22: 113-117.

Burke, R., M. Ewert, J. McLemore, D. Jackson. 1996. Temperature-Dependent Sex Determination and Hatching Success in the Gopher Tortoise (Gopherus polyphemus). Chelonian Conservation and Biology , 2: 86-88. Accessed December 01, 2013 at http://www.cnah.org/pdf_files/442.pdf .

Conant, R., J. Collins. 1998. Reptiles and Amphibians of Eastern/Central North America . New York, NY: Houghton Mifflin.

Diemer, J. 1986. The Ecology and Management of the Gopher Tortoise in the Southeastern United States. Herpetologica , 42: 125-133.

Ernst, C., J. Lovich. 2009. Turtles of the United States and Canada . Baltimore, Maryland: John Hopkins Univeresity Press.

Innes, R. 2009. "Gopherus polyphemus" (On-line). USDA Forest Service: Fire Effects Information System. Accessed December 02, 2013 at http://www.fs.fed.us/database/feis/animals/reptile/gopo/all.html .

Moon, J., E. McCoy, H. Mushinksy, S. Karl. 2006. Multiple Paternity and Breeding System in the Gopher Tortoise, Gopherus polyphemus . Journal of Heredity , 97: 150-157. Accessed December 06, 2013 at http://jhered.oxfordjournals.org/content/97/2/150.full.pdf+html .

Mushinsky, H., D. Wilson, E. McCoy. 1994. Growth and Sexual Dimorphism of Gopherus polyphemus in Central Florida. Herpetologica , 50: 119-128.

2012. "AnAge entry for Gopherus polyphemus" (On-line). AnAge: The Animal Ageing and Longevity Database. Accessed December 01, 2013 at http://genomics.senescence.info/species/entry.php?species=Gopherus_polyphemus .

Florida Fish and Wildlife Conservation Commission. Gopher Tortoise Management Plan. 2. Tallahassee, FL: Florida Fish and Wildlife Conservation Commission. 2012. Accessed December 01, 2013 at http://myfwc.com/media/2286685/GT-Management-Plan.pdf .

2013. "Gopher Tortoise: Gopherus polyphemus" (On-line). Florida Fish and Wildlife Conservation Commission. Accessed November 29, 2013 at http://myfwc.com/wildlifehabitats/profiles/reptiles-and-amphibians/reptiles/gopher-tortoise/ .

2013. "USGS Digital Elevation Maps" (On-line). Accessed December 01, 2013 at http://weather.unisys.com/usgs/ .