Demography of the Tortoise Gopherus polyphemus in Northern Florida

Abstract

-The demography of gopher tortoises (Gopherus polyphemus) in northern Florida was investigated from 1981 to 1987 through burrow surveys and mark-recapture efforts. The number of burrows showing active sign increased in April, peaked in July, and remained high through October. The burrow surveys also revealed a continuous cycle of burrow creation and abandonment. The ratio of captured gopher tortoises to burrows (active and inactive) varied among years and study sites; the range was 0.450.69. A total of 372 tortoises was captured, marked, and measured on three sites. Recapture rates for juveniles were consistently low. Percentages of adult tortoises in the three populations ranged from 40-62%. Female to male sex ratios of captured tortoises varied annually from 1:1 to 1:2. etology, Vol. 26, No. 3, p . 281-289, 19 2 Society for the Study of Amphibians and Reptiles t e Tortoise Gopherus polyphemus in Several studies have addressed the population biology of the gopher tortoise (Gopherus polyphemus) (Auffenberg and Iverson, 1979; Alford, 1980; Landers et al., 1980, 1982; Wright, 1982; Kushlan and Mazzotti, 1984; Wester, 1986; McCoy and Mushinsky, 1988). Population structure data have also been gathered in conjunction with gopher tortoise relocations (Burke, 1989a; Fucigna and Nickerson, 1989; Godley, 1989; Layne, 1989; Stout et al., 1989). Nonetheless, little information is available on demographic changes over time. The purpose of my study was to investigate gopher tortoise demography through burrow surveys and a mark-recapture effort. Specific objectives included determination of burrow use, population size structure, and sex ratios. MATERIALS AND METHODS Study Sites. -Gopher tortoise demographic data were gathered on three sites in northern Florida. I marked and recaptured tortoises during 1982-1986 on Roberts Ranch in Putnam County, 1981-1987 on Lochloosa Wildlife Management Area (WMA) in Alachua County, and 1985-1986 on Wolfe's Pasture, 0.6 km southeast of the Lochloosa WMA study site. The Roberts Ranch study site was 10.8 ha of eral studies have address d the populabiology of the gopher tor ise (Gopherus l phemus) (Auffenberg and Iverson, 1979; Ald, 1980; Landers et al., 1980, 1982; Wright, 2; Kushlan and Mazzotti, 1984; Wester, 1986; a l rger (ca. 160 ha) tract of sandhill habitat located approximately 15 km west of Palatka. The excessively-drained sand supported an overstory of scattered longleaf pines (Pinus palustris) and mature turkey oaks (Quercus laevis), a midstory of smaller turkey oaks, sand-live oaks (Q. geminata) and sand-post oaks (Q. margaretta), and a relatively diverse ground cover predominated by wiregrass (Aristida stricta), various composites (Asteraceae), and legumes (Fabaceae). The site remained unburned for more than seven years before a hot fire in 1983. The study area was bisected by a graded sand road constructed by the landowner in 1983. On Roberts Ranch, I removed 10 tortoises from their burrows within a fenced treatment plot in May 1982 to investigate tortoise population response to a simulated harvest. Of the 10 harvested tortoises (two females, six males, and two subadults), I subsequently released eight in sandhill habitat approximately 1.3 km southwest of the study area. However, one male returned. Following destruction of the treatment plot fence during road construction, I abandoned this portion of the study and expanded the study area from 7.6 ha to 10.8 ha. The Lochloosa WMA study site was a 1.1 km grassy roadside strip (20-40 m wide) and sura . a) tract of sandhi l habitat i atel 15 k west of Palatka. i l rai ed sand supported an s attered longleaf pines (Pinus paat re turkey oaks (Quercus laevis), s aller turkey oaks, sand-live oaks ) a sa d-post oaks (Q. margare ta), i l i erse ground cover predomi ass ( ristida stricta), various ( s e aceae), and legumes (Faba281 This content downloaded from 157.55.39.120 on Mon, 05 Sep 2016 04:09:48 UTC All use subject to http://about.jstor.org/terms