A Key­stone Species

The go­pher tor­toise’s bur­rows pro­vide refuge for other an­i­mals in peril

Times of the Islands - - Departments - BY WIL­LIAM R. C OX Wil­liam R. Cox has been a pro­fes­sional na­ture pho­tog­ra­pher and ecol­o­gist for more than 35 years. Visit him on­line at williamr­cox­pho­tog­ra­phy.com.

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.

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