Gopher Tortoise Demographic Responses to a Novel Disturbance Regime

The Journal of Wildlife Management 1–10; 2019; DOI: 10.1002/jwmg.21774

Research Article Gopher Tortoise Demographic Responses to a Novel Disturbance Regime

HUNTER J. HOWELL ,1,2 Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, USA BETSIE B. ROTHERMEL,2 Archbold Biological Station, 123 Main Drive, Venus, FL 33960, USA K. NICOLE WHITE, Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia, 180 E Green Street, Athens, GA 30602, USA CHRISTOPHER A. SEARCY, Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, USA

ABSTRACT The long‐term viability of gopher tortoise (Gopherus polyphemus) populations is jeopardized by increased urbanization and habitat degradation owing to fire suppression. Because the species’ remaining natural habitats in the southeastern United States exist within a mosaic of anthropogenic land uses, it is important to understand demographic responses to contrasting land uses and habitat management regimes. We examined differences in demographic parameters among fire‐suppressed sandhill, restored sandhill, and former sandhill (i.e., ruderal) land use‐land cover (LULC) types at Archbold Biological Station in south‐ central Florida, USA. Using Program MARK, we estimated population size, and sex‐specific and LULC‐specific survivorship based on 6 years of mark‐recapture data. We also analyzed individual growth trajectories and clutch sizes to determine whether growth rates or reproductive output differed among LULC types. Tortoises in an open, ruderal field occurred at a higher density (7.79/ha) than in adjacent restored (1.43/ha) or fire‐suppressed (0.40/ha) sandhill. Despite this higher density, both adult survivorship and body size were significantly higher in the ruderal field. Furthermore, the larger female body size in the ruderal field likely contributed to increased annual survivorship and slightly larger average clutch sizes. We did not detect offsetting negative demographic effects; in particular, we did not find significant biological or statistical differences in body condition, asymptotic body size, or growth rate among the 3 LULC types. Our results suggest that anthropogenic, grass‐dominated land‐cover types may be important components of the habitat mosaic currently available to this at‐risk species. © 2019 The Wildlife Society.

KEY WORDS demography, Gopherus polyphemus, habitat management, mowing, population ecology, prescribed ﬁre.

The leading causes of biodiversity loss across the globe are generally associated with longleaf pine (Pinus palustris) habitat destruction and degradation, exacerbated by an ex- savanna or sandhill ecosystems (Auffenberg and Franz ponential increase in the human population (Foley et al. 1982, Diemer 1986). The gopher tortoise is a keystone 2011, Haddad et al. 2015). Whereas outright habitat loss has species that alters ecosystems by digging extensive burrow obvious negative conservation implications, effects of habitat systems that serve as habitat for >350 vertebrate and in- fragmentation, and how best to manage small populations vertebrate species (Eisenberg 1983, Jackson and Milstrey isolated by fragmentation, are difficult to assess and are 1989, Witz et al. 1991, Johnson et al. 2017). Despite their debated in the literature (Resasco et al. 2017). Preventing integral role in native ecosystems of the Southeast, gopher isolated populations from dropping below a minimum viable tortoises, like most other turtles, are threatened by decades population size is important to avoid extinction vortexes and of habitat loss, poor habitat management, and human har- to ensure long‐term species persistence to maintain global vest, which have caused declines across their range (Diemer biodiversity (Shaffer 1981). In many instances, however, it 1986, Klemens 2000, Ernst and Lovich 2009, Lovich et al. may not be possible to implement the management strategy 2018). The greatest current threats to the species’ viability that would be most beneficial to the species in question are habitat loss, caused by increased urbanization, and because of resource limitations, stakeholder conflicts, the habitat degradation due to fire suppression (Mushinsky socio‐political climate, or a combination of these factors et al. 2006). Overgrown forest conditions, resulting from (Wilson et al. 2006, Traill et al. 2010). lack of appropriate fire management, have led to lower Gopher tortoises (Gopherus polyphemus) are denizens of the tortoise densities, more abandoned burrows, and decreased southeastern Coastal Plain of the United States and are population sizes (Auffenberg and Franz 1982, Diemer 1989). Range‐wide habitat fragmentation and associated habitat degradation have led to many populations inhabiting Received: 19 March 2019; Accepted: 10 September 2019 habitat islands surrounded by agricultural or urban land uses 1 ( ) E‐mail: [email protected] Mushinsky and McCoy 1994, Ennen et al. 2011 . Within 2These authors contributed equally to the manuscript. these islands, a lack of surrounding habitat is coupled with

Howell et al. • Gopher Tortoise Demography in Modified Sandhill 1 behavioral avoidance of adjacent closed‐canopy vegetation, of the Lake Wales Ridge in Highlands County, Florida which leads to skewed densities and increased population (27.19°N, 81.34°W). The study area has a subtropical cli- isolation (Mushinsky and McCoy 1994, McCoy and mate with >60% of annual precipitation falling during the 4 Mushinsky 2007, McCoy et al. 2013). Because of these wettest months (Jun–Sep). Between 1958 and 2017, annual threats, the gopher tortoise is federally listed as threatened rainfall averaged 1,355 mm, with mean monthly rainfall of in the extreme western portion of its range and currently 168 mm during May–October and 57 mm during under review for listing in the remaining eastern portion of November–April. Mean daily maximum and minimum its range (U.S. Fish and Wildlife Service 1987, 2011). temperatures were 32.8°C and 19.3°C in summer and Ideally, gopher tortoise habitat is managed predominantly 26.1°C and 11.0°C in winter (ABS manual weather data, through the application of prescribed fire to reduce mid‐story 1958–2017; www.archbold‐station.org/data/, accessed 8 vegetation, increase spacing between canopy trees, promote Jul 2019). production of herbaceous groundcover, and increase thermo- A slash pine‐turkey oak (Pinus elliottii var. densa–Quercus regulatory opportunities (Diemer 1986, Yager et al. 2007). laevis) vegetation community, known as southern ridge Habitats with dense herbaceous groundcover comprised of sandhill, occurs on the well‐drained, sandy soils of Red Hill abundant grasses, legumes, and other nutritious, low‐growing at elevations of 54–64 m (Abrahamson et al. 1984; Fig. 1). plants provide optimal food resources for gopher tortoises Historically, the modal fire return interval for this py- (MacDonald and Mushinsky 1988). The use of prescribed fire, roclimax community was 2–5 years, whereas the sur- however, is plagued with concerns about smoke management, rounding sand pine (Pinus clausa) scrub would have burned lowered air quality, potential damage to private property, and infrequently, on the order of every 20–100 years (Menges poor public perception, particularly in urbanized areas (Yager et al. 2017). Following a severe wildfire in 1927, however, et al. 2007, Yoder et al. 2007).Asaresult,fire suppression has fires on Red Hill were actively suppressed until ABS ini- become a widespread management problem for many py- tiated a prescribed burning program and began re- roclimax species, including the gopher tortoise. introducing fire to selected sandhill units between 1989 and In Florida, USA, a stronghold of the gopher tortoise’s 1993 (Ashton et al. 2008). remaining populations (Allison and McCoy 2014), losses of The management units within our 136‐ha study area can native uplands exceed 80% (Sprott and Mazzotti, 2001), be categorized into 3 land use‐land cover (LULC) types: and the remaining natural land cover falls within a mosaic of fire‐suppressed sandhill, restored sandhill, and ruderal agricultural and urbanized land uses (Diemer 1987). Within (Fig. 1). Nearly half of the fire‐suppressed sandhill area has the Lake Wales Ridge, a fire‐adapted scrub and sandhill not burned since 1927, and the remainder has been burned ecosystem vital for gopher tortoises in central Florida, ap- only 1–3 times since 1989. As a result of decades of fire proximately 85% of native vegetation has been lost through suppression, cover of sand pines increased, creating closed‐ urbanization and agricultural development (Turner et al. canopy conditions and reducing herbaceous groundcover 2006). As Florida’s human population continues its rapid (Ashton et al. 2008). Areas categorized as restored sandhill growth (U.S. Census Bureau 2017), the amount of gopher were historically fire‐suppressed but have been undergoing tortoise habitat that becomes part of the non‐native matrix restoration since 2013 using a combination of mechanical will continue to increase. Understanding how to manage clearing and prescribed fire (2–3 burns between 2012 and remnant habitats in an urbanized or agricultural matrix, 2017). Hill Garden, a 4.5‐ha unit of ruderal vegetation on where there may be resistance to use of prescribed fire, will the top of Red Hill, has been maintained for several decades be critical to ensuring that these areas can support viable as an open field by mowing. Initially cleared in the 1940s, tortoise populations into the future. the unit was planted with non‐native bahiagrass (Paspalum We examined demographic responses to habitat mod- notatum) and used for small‐scale agricultural production ification and disruption of the natural fire regime in a rel- (i.e., exotic fruits and vegetables). Since removing crop atively small, semi‐isolated gopher tortoise population in species in the 1990s, ABS has managed Hill Garden using a southern Florida. Our objective was to clarify the con- combination of mowing, prescribed fire (7 burns since sequences of skewed population densities and the role of 1990), and selective use of herbicides to control invasive mowed, ruderal fields for long‐term population persistence exotics. The eastern section of ABS containing Red Hill is by describing within‐population demographic variation surrounded on 3 sides by citrus groves and is bordered on among habitat patches subjected to contrasting manage- the west by a 2‐lane, public road, which is a semi‐permeable ment regimes. We predicted that extreme habitat barrier to tortoises attempting to move between Red Hill heterogeneity within our study site would result in within‐ and other natural communities on ABS. population variation in demographic rates. Specifically, we expected higher growth rates, body sizes, and survivorship METHODS in restored versus fire‐suppressed sandhill, and we expected even greater positive responses to ruderal conditions. Population Monitoring and Tortoise Capture The Red Hill gopher tortoise population is the focus of an STUDY AREA ongoing mark‐recapture study initiated in 1967 (Layne 1989). Our study population inhabits Red Hill at Archbold Bio- During the most‐recent census from 2012 to 2017, we em- logical Station (ABS), which is located at the southern end ployed multiple approaches to monitor the population,

2 The Journal of Wildlife Management Figure 1. Land use‐land cover types in the gopher tortoise monitoring area (shaded regions in left panel) at Archbold Biological Station, south‐central Florida, USA, 2012–2017. Right panel shows non‐collapsed tortoise burrows mapped in Hill Garden and surrounding sandhill units in 2014, approximately 1 year after the first restoration burn but prior to any mechanical clearing. including burrow surveys, radio‐tracking of a subset of adults Garden. For this calculation, we included only non‐ (for a separate study), and repeatedly driving firelanes and collapsed burrows that we classified as active or usable per roads to search for tortoises along the perimeters of units definitions in Castellón et al. (2012). within the study area. We focused our capture‐mark‐recapture During burrow surveys we routinely captured and marked efforts on a study area with 3 land cover types (Fig. 1).Outside any new tortoises and recorded resightings of marked tor- the focal area (Fig. 1), we recorded opportunistic encounters toises. We also scoped active burrows and attempted to and resightings, typically of tortoises crossing firelanes or roads. identify resident tortoises using a customized burrow From 2012 to 2017, we completed 5 annual burrow sur- camera system (Environmental Management Services, veys of Hill Garden, 4–6 annual burrow surveys of every Canton, GA, USA). Year‐round monitoring of 37 radio‐ restored unit, and 0–1 burrow surveys of fire‐suppressed tagged female tortoises residing in Hill Garden and adjacent units during the most‐active season for tortoises (Apr–Sep). units, beginning in spring 2015, required weekly visits to The burrow surveys entailed walking closely spaced trans- Red Hill that yielded many opportunistic captures and re- ects to cover the entirety of each unit, which took up to captures of additional tortoises. We did not include tele- 6 days depending on area of the unit. We recorded all metry observations in the capture histories analyzed for this burrow locations using a GeoExplorer 3000 global posi- study. In most years we also periodically drove firelanes tioning system unit (Trimble, Sunnyvale, CA, USA) and during the active season to locate additional tortoises that staked each non‐collapsed burrow. We also measured may have been missed by other methods, particularly those burrow width at a depth of 50 cm using calipers (Martin and living on the periphery of the survey area. We used tortoise Layne 1987). Burrow‐width distributions are a useful proxy locations, whether from physical capture or opportunistic for population size structure, given the strong correlation resightings, to assign the primary residency of each in- between burrow width and carapace length of resident tor- dividual to ruderal field (Hill Garden), restored sandhill, or toises (Alford 1980) and our greater success in detecting fire‐suppressed sandhill. juvenile‐sized burrows (width <13 cm) than in capturing We typically captured tortoises by hand but occasionally juvenile tortoises. We calculated proportions of burrows in found it necessary to trap them using Havahart live animal different size classes in 2015, a year when we mapped traps (Woodstream Corporation, Lititz, PA, USA) placed burrows in all restored sandhill units in addition to Hill at burrow entrances. Following methods instituted by

Howell et al. • Gopher Tortoise Demography in Modified Sandhill 3 previous researchers and similar to those of Cagle (1939), (254 mm CL; Rothermel and Castellón 2014). Although we marked new tortoises by drilling holes in unique com- male tortoises at ABS may reach physiological maturity at binations of marginal scutes. Upon first capture, we also 210 mm CL (Meshaka and Layne 2015), the smallest male collected a blood sample via the subcarapacial vein found to sire any offspring in 2015–2016 was 260 mm CL (Hernandez‐Divers et al. 2002) for subsequent genotyping (White et al. 2018). We tested for differences in survivorship described by White et al. (2018). When possible, we ob- between size classes and among LULC types by determining tained annual measurements of each tortoise, including if the 95% confidence interval for the difference between 2 mass (to the nearest 0.1 kg for adults and 0.01 kg for im- sample parameter estimates included zero. matures) using a spring scale and straight‐line carapace length (CL), carapace width, plastron length, and shell Body Size, Body Condition, and Clutch Sizes height to the nearest 1 mm using calipers. During handling, We performed an analysis of variance (ANOVA) to test for a male tortoise sometimes extruded its penis, otherwise we differences in adult body size (CL) among LULC types. determined sex based on secondary sexual characteristics Additionally, we used JMP (Pro 14, SAS Institute, Cary, (i.e., plastral concavity of mature males; McRae et al. NC, USA) to fit the Von Bertalanffy growth model to 1981a). All tortoise handling and procedures complied with tortoise size trajectories from each LULC type, using the Florida Fish and Wildlife Conservation Commission sci- CL recorded at first and last captures during our study pe- entific collecting permits (LSSC‐10‐00043) and protocols riod (2012–2017) to maximize the potential recorded approved by Institutional Animal Care and Use Commit- growth. We excluded individuals that did not have multi‐ tees at Archbold (ABS‐AUP‐014‐R) and University of year growth records and those that had an overall negative Georgia (A2014 05‐024‐Y3). recorded growth as a result of measurement error (only 8% of individuals). Von Bertalanffy models often provide a Population Modeling better fit than logistic models to growth data from long‐ We estimated apparent survival rates, population sizes, and lived reptiles, and previous studies have analyzed gopher population growth rates (λ) using Program MARK (White tortoise growth using these models (Mushinsky et al. 1994, and Burnham 1999). We used a POPAN formulation of Aresco and Guyer 1999, Tuberville et al. 2014). the Jolly‐Seber model to estimate annual survivorship rates We used 2 methods to calculate body condition. First, we and population sizes, and a Pradel‐λ formulation of the calculated a mass:volume ratio, where volume is defined as Jolly‐Seber model to estimate population growth rates. We CL × carapace width × shell height, as reported for other binned capture histories from each year into a single binary gopher tortoise populations in south‐central Florida value of 0 or 1 to form encounter histories. For example, an (McCoy et al. 2011, Rothermel and Castellón 2014). individual captured in 2012, 2014, and 2017 received an Second, we calculated residuals from a linear regression of encounter history of 101001. For the POPAN for- log(mass) versus log(volume) of tortoises (Jakob et al. 1996). mulations, we considered a candidate set of 16 models for During handling, tortoises often urinated or defecated. To each of the LULC types. For both survivorship and re- ensure that this excretion did not bias our body condition capture probability, we considered models with constant, indices, we calculated residuals from an analysis of co- time varying, sex varying, and time and sex varying rates. variance (ANCOVA) that included excretion category To prevent lack of model convergence due to over- (i.e., no excretion, defecation, urination, or both) as a fixed parameterization, we assumed constant emigration and effect and log(volume) as the covariate. We used 2 × 3 immigration rates and population size (N) across years. We factorial ANOVA to compare both measures of body con- then used the corrected Akaike’s Information Criterion dition between sexes and among LULC types, excluding 9 ( ) AICc to rank the models and used model averaging to adults that moved frequently between LULC types. Because ‐ ‐ produce parameter estimates from the models whose AICc of high intra and inter annual variability in weather, we weight was greater than 0.01. We removed models that used body condition data only from the late dry season (Jan– failed to converge from the model‐averaging process. For Apr), and analyzed 2015 (a relatively wet year) and 2017 (a the Pradel‐λ formulation, we considered the same set of 16 relatively dry year) separately. candidate models. For each LULC type, we used Program During spring‐summer, 2015–2016, we located nests by RELEASE within Program MARK to test the goodness of carefully excavating the soil mounds at the entrances of non‐ fit of our data to the assumptions of the Jolly‐Seber models. collapsed burrows within Hill Garden and adjacent units. These goodness‐of‐fit tests showed no evidence that there We protected nests found in May–June with plastic hard- were violations of the assumptions of the Jolly‐Seber ware cloth, re‐covered with soil and left the hardware cloth models. in place until July–August, when we collected and trans- To examine differences in apparent survival between size ferred clutches to incubators in the laboratory. We main- classes, we classified individuals as immature (CL < 250 mm) tained eggs through hatching in incubators kept at or adult (CL > 250 mm). This size threshold corresponds to approximately 80% humidity and 28–30°C, which is the the minimum size of female tortoises with oviductal eggs at approximate pivotal temperature for sex determination in our study site (252 mm CL; Meshaka and Layne 2015) and gopher tortoises (Demuth 2001). For genotyping and con- the minimum size of gravid females in another south‐central firmation of maternity and paternity, we collected blood Florida population occupying similar land cover types samples from hatchlings and tissue from inviable eggs.

4 The Journal of Wildlife Management Additional methodological details are available in White of annual population growth rates did not differ significantly et al. (2018). Eight clutches in 2016 belonged to females between any of the LULC types. We estimated there were 113 that also produced clutches found in 2015. For our stat- adult gopher tortoises (95% CI = 109–123) in our population, istical analyses, we used data from the largest clutch pro- including 35 adults in Hill Garden, 38 adults in the restored duced by each of these individuals. We used ANOVA to areas, and 38 adults in the fire‐suppressedareas.Thiscorre- determine whether clutch size differed between ruderal field sponds to densities of 7.9 tortoises/ha in Hill Garden (95% and sandhill, and ANCOVA to determine whether re- CI = 7.9–7.9), 1.4 tortoises/ha in restored sandhill (95% CI = productive effort (clutch size corrected for body size) dif- 1.35–1.61), and 0.40 tortoises/ha in fire‐suppressed sandhill fered between these LULCs. For both analyses, we pooled (95% CI = 0.32–0.66; Table 1; Fig. 2B). Sex and time were data from the restored and fire‐suppressed sandhill units commonly supported as variables predicting recapture proba- because of sample size constraints. We conducted statistical bility (Tables S1 and S2, available online in Supporting In- analyses in JMP or SPSS (version 22, IBM, Armonk, formation). NY, USA). Size Distribution and Growth Rates RESULTS Based on burrow widths, the Red Hill tortoise population is ‐ ( ) - Between 2012 and 2017, we recorded 1,039 captures of 125 dominated by adult sized individuals Fig. 3 , though bur juvenile, subadult, and adult gopher tortoises. Additionally, rows in immature size classes made up approximately 21% we marked and released 194 hatchlings (≤10 days old) from of burrows in Hill Garden and 17% of burrows in restored fi ff - eggs incubated in 2015–2016. In 2017, 71 out of the 74 sandhill. There was a signi cant di erence in the size dis individuals we encountered (96%) were recaptures. The tribution of burrows in Hill Garden compared to restored ( 2 2 = population was slightly female‐biased, with an overall sex sandhill χ contingency table analyses, χ 12 34.0, < ) - ratio of 0.77:1 (male:female). Hill Garden had the most P 0.001 , with Hill Garden having more large adult bur ( – ) strongly female‐biased sex ratio of 0.67:1, and the fire‐ rows 36 47 cm width and restored sandhill having more ( – ) suppressed units had the least biased sex ratio (0.92:1). small adult burrows 28 35 cm width . However, none differed significantly from each other (χ2 The average adult female CL across the entire population ( = – ) contingency test, P > 0.05) or from the expected 1:1 ratio was 304 mm 95% CI 295 313 mm and mean CL ff ( = < ) (χ2 goodness‐of‐fit test, P > 0.05). di ered among LULC types F2,53 8.59, P 0.001 . Post hoc Tukey‐Kramer comparisons identified that female Survivorship and Population Size tortoises in the ruderal field (CL: x¯ = 326 mm) were sig- Average male apparent survival across the entire population was nificantly larger than female tortoises in restored (CL: x¯ = 94.2% (95% CI = 87.6–97.1%) and average female apparent 290 mm, P = 0.002) and unrestored (CL: x¯ = 294 mm, survival was 92.8% (95% CI = 87.6–95.9%; Table 1).Thees- P = 0.001) sandhill, but females in restored and unrestored timated population growth rate was 1.00 (95% CI = 0.93–1.07) sandhill were similar in body size (P = 0.92; Fig. 2C). The for males and 0.91 (95% CI = 0.78–0.96) for females across the asymptotic mean body size for the entire population was entire population. For LULC‐specific estimates, we excluded 332 mm (95% CI = 320–353 mm), and the characteristic 7maleand2femaleadulttortoisesbecausetheyspentsig- mean growth constant was 0.08 (95% CI = 0.052–0.12). nificant time in >1LULCtype(i.e., >10% of their capture Although Hill Garden females had the largest asymptotic locations were in a contrasting type) or were captured in fire- mean body size (346 mm, 95% CI = 329–399 mm), it was lanes that bordered >1 LULC type. Annual apparent survi- not significantly different from the estimates for females in vorship of both sexes was significantly higher in Hill Garden restored sandhill (316 mm, 95% CI = 300–341 mm) or fire‐ than in either the restored or fire‐suppressed sandhill (Table 1; suppressed sandhill (316 mm, 95% CI = 293–367 mm). Fig. 2A). Additionally, annual survivorship of immature tor- Likewise, although the characteristic mean growth con- toises (73.8%, 95% CI = 56.3–86.1%) was significantly lower stants and rates varied among LULC types (range: than that of adults (93.4%, 95% CI = 88.6–96.9%).Estimates females = 0.050–0.200 or 2–3 mm/yr, males = 0.096–0.289

Table 1. Comparison of adult gopher tortoise demographic parameter estimates among land use‐land cover types in the Red Hill study area at Archbold Biological Station, Florida, USA, 2012–2017. We present 95% conﬁdence intervals in parentheses.

Apparent survival Estimated density (tortoises/ha) Management unit Females Males Females Males Population growth rate (λ) Whole population (n = 109) 0.93 0.94 0.42 0.32 0.98 (0.88–0.96) (0.88–0.97) (0.41–0.47) (0.31–0.37) (0.87–1.00) Hill Garden (n = 34) 0.99 0.99 4.90 2.95 1.04 (0.98–1.00) (0.98–1.00) (4.90–4.90) (2.95–2.95) (0.98–1.09) Restored sandhill (n = 37) 0.95 0.94 0.92 0.48 1.01 (0.86–0.98) (0.84–0.97) (0.88–1.36) (0.48–0.48) (0.88–1.09) Fire‐suppressed sandhill (n = 29) 0.80 0.79 0.21 0.19 0.93 (0.66–0.89) (0.67–0.89) (0.15–0.32) (0.16–0.34) (0.76–1.15)

Howell et al. • Gopher Tortoise Demography in Modified Sandhill 5 Figure 2. Comparison of demographic parameters for female gopher tortoises from 2012–2017 across land use‐land cover (LULC) types at Archbold Biological Station in south‐central Florida, USA. Dots represent mean values and bars represent 95% confidence intervals. Significant differences between LULC types are signified by letters. or 2–3 mm/yr), they did not differ significantly for either In 2015–2016, we collected and confirmed maternity of 29 sex. Measurements of the few juveniles captured more than intact clutches (14 inside Hill Garden and 15 outside Hill once suggest they are capable of faster growth in Hill Garden) averaging 8.7 ± 2.3 (SD) eggs per clutch. Clutches Garden (2.2–3.0 mm CL/month; n = 2) than in restored in Hill Garden were larger (9.6 ± 2.5) than in sandhill (7.9 sandhill (1.2–1.6 mm CL/month; n = 2). ± 1.9 eggs), but this difference was not statistically sig- fi ( = = ) ( = ni cant either before t19 1.8, P 0.09 or after F1,18 0.052, P = 0.82) accounting for differences in female body Body Condition and Clutch Sizes size. As expected, there was a significant, positive relation- Mean mass:volume ratios for females in 2017 were 0.607 (95% ship between female size (log‐transformed CL) and the log‐ 2 CI = 0.598–0.618) for Hill Garden, 0.608 (95% CI = 0.598– transformed number of eggs per clutch (R = 0.61, n = 21, 0.618) for restored sandhill, and 0.614 (95% CI = 0.599–0.628) P < 0.001). for fire‐suppressed sandhill. Mean mass:volume ratios for males in 2017 were 0.595 (95% CI = 0.580–0.609) for Hill Garden, DISCUSSION 0.608 (95% CI = 0.593–0.622) forrestoredsandhill,and0.596 Our study provides new insights regarding the demographic (95% CI = 0.581–0.612) for fire‐suppressed sandhill. Females consequences of alternative habitat management strategies for ( = ‐ fi had higher body condition than males in the wet year F1,17 gopher tortoise populations in human modi ed landscapes. 4.6, P = 0.041). Otherwise, there were no biological or stat- Tortoises within the ruderal field of Hill Garden persist istically significant effects of LULC type (Fig. 2D),sex,ortheir at much higher density (7.9/ha) than observed in restored interaction on either mass:volume ratio or residual body con- (1.4/ha) or fire‐suppressed (0.4/ha) sandhill, while maintaining dition in either 2015 or 2017 (P > 0.05; n = 23 or 33, higher survivorship rates and statistically indistinguishable body respectively). condition and asymptotic body size (Table1;Fig.2).This

6 The Journal of Wildlife Management sites broadly classified as pasture (i.e., herbaceous‐ dominated land cover including wildlife openings) were the sites most likely to contain gopher tortoise burrows at Fort Benning, Georgia. Similarly, in areas with high tree and understory density, gopher tortoises generally migrate to open ecotones, clear‐cuts, and young open‐canopy plantations (Logan 1981, Auffenberg and Franz 1982, Campbell and Christman 1982, Diemer 1986). Although we conducted relatively fewer formal burrow surveys of fire‐suppressed units, we do not think this re- sulted in non‐detection of tortoises and underestimation of densities in restored or fire‐suppressed sandhill. The closed‐ canopy conditions created by high densities of sand pines and other trees made the interiors of long‐unburned units highly unsuitable as habitat for gopher tortoises. A previous study conducted by Ashton et al. (2008) in 2001–2002 found that the number of active burrows declined to a mean density of 0.4/ha in Red Hill units burned <2 times in the preceding 18 years. The most likely explanation was that tortoises had emigrated out of those units in response to fire suppression, as observed in other studies (Auffenberg and Franz 1982, Mushinsky and McCoy 1994, Aresco and Guyer 1999). During our study, we observed that the few Figure 3. Size frequency histograms for gopher tortoise burrows in a tortoises found in long‐unburned units prior to restoration ruderal field (Hill Garden) and sandhill being restored at Archbold tended to live in close proximity to the edges of firelanes, ‐ Biological Station in south central Florida, USA. Histograms are based on where there was still herbaceous food and open areas for width measurements of all non‐collapsed burrows found in Hill Garden (n = 85) and restored sandhill units (n = 54) during summer 2015 surveys. thermoregulation, and where we had a high chance of capturing them at least once during the 6 years of our study. For these reasons, and because we relied on multiple difference was large enough to likely affect long‐term pop- methods to locate tortoises, we do not think differences in ulation persistence (Congdon et al. 1994, Miller 2001, burrow survey effort affected our results. Tuberville et al. 2009, Howell and Seigel 2019). The densities On average, tortoises inhabiting Hill Garden had larger and survivorship rates we estimated for gopher tortoises within clutch sizes than those in adjacent sandhill, a pattern that Hill Garden are among the highest reported in the literature for was largely explained by the biologically significant increase this species across its range (Table S3). Females residing in Hill in fecundity associated with larger female body size. The Garden also tended to attain larger body sizes, resulting in trend toward larger asymptotic body sizes in Hill Garden slightly higher reproductive output in terms of clutch size; and observed skew in burrow sizes (Fig. 3) was likely the specifically, Hill Garden clutches exceeded sandhill clutches by result of resident individuals having excellent growth op- an average of 1.7 eggs. These results suggest that Hill Garden portunities as juveniles and subadults and thus reaching provides high‐quality forage and prime habitat for adult tor- larger sizes at maturity. The mean clutch size we observed toises. Indeed, the persistence of this gopher tortoise population (8.7 ± 2.3 eggs) is higher than the mean of 6.5 eggs reported through more than 6 decades of fire suppression and deterio- by Ashton et al. (2007) for the ABS population, likely be- rating habitat conditions was facilitated by the existence of this cause the CL of females in their smaller sample averaged anthropogenic clearing. However, the availability of neigh- 4 cm less than the CL of females in our sample. These boring native land cover types may also be key to long‐term findings are consistent with several other studies that have persistence, depending on the habitat needs of young life stages, documented higher reproductive output of gopher tortoises which were under‐sampled in the current study. in improved pastures and ruderal fields (Diemer and Moore Our results are consistent with other studies showing that 1994, Small and MacDonald 2001, Hathaway 2012). grass‐dominated vegetation associations, managed either Even though we have documented that Hill Garden cur- by mowing or grazing, provide important habitat for go- rently supports a greater density of tortoises than the sur- pher tortoises in landscapes where well‐managed, native rounding restored and fire‐suppressed sandhill, and does so land cover types are scarce. For example, gopher tortoises without any obvious demographic tradeoffs, we do not want readily use roadsides and utility rights‐of‐way (McRae to suggest that the system is currently in equilibrium. et al. 1981b, Berish et al. 2012, Rautsaw et al. 2018). Rather, our fire‐restored areas have likely not been under a Tuberville et al. (2008) remarked that a pasture maintained managed fire regime for long enough to reach equilibrium by mowing was the primary area of habitat for the gopher through either immigration of adults or recruitment of ju- tortoises at their study site on St. Catherines Island, veniles. The simple reintroduction of fire to areas that suf- Georgia, USA. Baskaran et al. (2006) also reported that fered long‐term fire suppression may not result in an

Howell et al. • Gopher Tortoise Demography in Modified Sandhill 7 immediate return to pre‐burned conditions, in terms of remain. As with prescribed fire, demographic responses to vegetation community composition and amount of open mowing or other mechanical disturbance regimes are likely to ground (Abrahamson and Abrahamson 1996a, b; Menges vary depending on the frequency and timing of the dis- and Hawkes 1998; Yager et al. 2007; Ashton et al. 2008). turbance. Future studies should examine the effect of habitat One‐time applications of prescribed fire may not increase management on young age classes and how predation risk the amount of herbaceous forage sufficiently (Yager et al. and forage quality for juveniles varies as a function of vege- 2007), and tortoise densities are not always correlated with tation structure and composition (Pike 2006, Hathaway time‐since‐fire (Breininger et al. 1994, Mushinsky et al. 2012). On Red Hill, the close juxtaposition of native sandhill 2006). Assuming ABS’s restoration efforts are successful, we allows for individual tortoises to take advantage of resources expect that population densities in the sandhill units will in multiple land cover types (i.e., landscape supplementation; continue to increase, whereas density in Hill Garden may Dunning et al. 1992). In general, more research is needed decrease as additional habitat becomes available (Mushinsky regarding the effects of such habitat heterogeneity, and the and McCoy 1994). Furthermore, repeated applications of broader landscape context. Properties of the surrounding fire should promote wiregrass (Aristida spp.) and other matrix are likely to be important factors affecting persistence forage species (MacDonald and Mushinsky 1988, Reinhart of small, isolated populations (Wolf et al. 2013, Resasco et al. and Menges 2004), which eventually may facilitate attain- 2017). For example, the relative proportions of agricultural ment of larger body sizes and clutch sizes in the restored and urban land uses may affect predator community com- sandhill units relative to fire‐suppressed sandhill (Rostal and position, particularly abundance of raccoons (Procyon lotor) Jones 2002). and other mesopredators that prey on tortoise eggs and young Although the high density in Hill Garden had no apparent (Wilson 1991, Butler and Sowell 1996, Smith et al. 2013). demographic costs for the parameters we investigated, other subtle effects may be occurring. Spatial concentration of fe- MANAGEMENT IMPLICATIONS males may enable males to engage in female defense polygyny Our results offer hope that alternative habitat management (Douglass 1986), which has implications for the mating system strategies can maintain robust gopher tortoise populations and population genetics. White et al. (2018) observed large where socio‐political factors may prevent prescribed burns disparities in male reproductive success in the Red Hill tortoise from being conducted at the scale or frequency of historical fire population (i.e., high reproductive skew in favor of larger regimes. At our study site, maintaining a large patch of ruderal males), which can reduce effective population size and genetic field by mowing has been beneficial for persistence and re- diversity. Furthermore, the frequency of negative intraspecific production of gopher tortoises. However, use of such open interactions may increase when tortoises are forced to live at areas may expose gopher tortoises to negative interactions with high densities in small habitat patches (McRae et al. 1981b). humans and result in increased mortality from human activities Conversely, at low densities, males are forced to make longer or predation. Therefore, when establishing or maintaining movements to find mates and the potential for social inter- open‐canopy tortoise habitat using mechanical methods, actions declines (Guyer et al. 2012). managers should be attuned to minimizing subsequent human Intermediate size classes are under‐represented in the Red Hill effects. Given the largely human‐modified mosaic of land population (Fig. 3), similar to a population in Georgia assessed cover types currently available to gopher tortoises, areas 40 years after an isolating event (i.e., construction of a reservoir maintained by mowing or other mechanical means may per- that consigned a small population of tortoises to an island; form a critical role in supplementing native land cover types to Ennen et al. 2011). In contrast, 10 populations in northern conserve gopher tortoise populations. peninsular Florida tended to have high proportions of tortoises in intermediate size classes (Alford 1980).Wesuspectourstudy ACKNOWLEDGMENTS population is at carrying capacity, resulting in higher dispersal This article is dedicated to J. N. Layne (1926–2017) in and emigration of subadults, which may be disadvantaged in recognition of his 27 years of tortoise research at ABS. We social interactions with larger adults (McRae et al. 1981b, are grateful to T. D. Tuberville for training on field Tuberville et al. 2014). As implied by the very high apparent methods and K. R. Zamudio for guidance and use of lab survival estimates for tortoises in the ruderal field, adults tor- facilities for genotyping. We also thank K. Ewing for da- toises in Hill Garden exhibited a high degree of site fidelity. tabase development; K. Main, B. Crawford, and ABS Although we have documented only 3 instances of permanent Operations and Maintenance staff for implementing land emigration out of the Red Hill study area in the past 10 years management and restoration practices; and the following (2008–2017), unobserved emigration from peripheral sandhill people for assisting with data collection and fieldwork: units may have contributed to the observed disparity in apparent M. Behrendt, K. Buhlmann, A. Chang, C. Dale, S. Dean, survival between ruderal and sandhill LULC types. C. Debevec, S. Dillon, L. Elston, A. Fassler, Z. Forsburg, Even though our conclusions fit well with the existing lit- L. Gette, E. Jones, G. Kamener, S. King, K. Moses, erature documenting the potential benefits of using me- E. Noel, C. Noss, B. Price, A. Rivero, S. Rothermel, chanical clearing to create anthropogenically maintained, E. Royal, N. Salvatico, E. Shadle, L. Siegle, Z. Steele, early‐successional vegetation for gopher tortoises and other T. Tuberville, R. Tucker, M. White, M. Yuan, and herpetofauna (Campbell and Christman 1982, Meshaka and K. Zamudio. We also thank C. Mothes and S. Clements for Layne 2002, Cantrell et al. 2013), important questions feedback and comments on the manuscript. This research

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