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Breeding Biology of a Florida Population of Ambystoma cingulatum (Flatwoods Salamander) During a Drought
John G. Palis, Matthew J. Aresco, and Sandra Kilpatrick

Southeastern Naturalist, Volume 5, Number 1 (2006): 1–8

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2006 SOUTHEASTERN NATURALIST 5(1):1–8 Breeding Biology of a Florida Population of Ambystoma cingulatum (Flatwoods Salamander) During a Drought JOHN G. PALIS1,*, MATTHEW J. ARESCO2, AND SANDRA KILPATRICK3 Abstract - Successful long-term monitoring programs of amphibians require the ability to distinguish natural population fluctuations from human-caused declines. Because recruitment in populations of pond-breeding amphibians depends on optimal environmental conditions of rainfall and hydroperiod, extended periods of drought may have adverse effects. We examined the breeding biology of Ambystoma cingulatum at a breeding site in northwestern Florida for four consecutive seasons (1999–2002) during and immediately following a drought. The number of immigrating adults declined steadily during this period, and larvae and metamorphs were not observed. Potential explanations for the observed decline in number of adults include disruption of migration as a result of insufficient rainfall during the breeding season and cumulative rainfall deficit, lack of juvenile recruitment, and adult attrition. We believe reduction in number of adults is best explained as attrition of adults without recruitment of juveniles. Introduction Reports of worldwide amphibian declines emphasize the importance of distinguishing natural fluctuations in amphibian populations from those resulting from human activities (Blaustein 1994, Pechmann and Wilbur 1994, Pechmann et al. 1991). Among natural causes of population fluctuations in amphibians, periodic drought is a recurring stress (Stahle et al. 1988). Drought affects pond-breeding amphibians by interfering with breeding migration of adults (Semlitsch 1985, Semlitsch et al. 1996) and by destroying eggs or larvae due to shortened hydroperiod (Newman 1987; Petranka and Petranka 1981; Seale 1982; Semlitsch 1983, 1987; Shoop 1974). At its extreme, drought has been implicated in the decline or extirpation of amphibian populations (Corn and Fogleman 1984; Dodd 1993, 1995; Kagarise Sherman and Morton 1993; Semlitsch et al. 1996). Ambystoma cingulatum (Cope) (Flatwoods Salamander), a Federallythreatened species (US Fish and Wildlife Service 1999), inhabits mesic Pinus palustris P. Mill. (longleaf pine)-Aristida stricta Michx. (wiregrass) savannas and flatwoods from southern South Carolina, through the lower coastal plain to southern Alabama (Conant and Collins 1991). Adults migrate to isolated wetlands to breed from October through December (Anderson and Williamson 1976, Means et al. 1996, Palis 1997a). The larval period lasts 3 to 4 months, typically from December or January through March (Palis 1995). Although adults spend approximately 90% of the year in nonbreeding habitat (Palis 1997a), little is known about this phase of the life cycle. 1PO Box 387, Jonesboro, IL 62952. 2Department of Biological Science, Florida State University, Tallahassee, FL 32306. 3National Forests in Mississippi, 100 West Capital Street, Suite 1141, Jackson, MS 39206. *Corresponding author - 2 Southeastern Naturalist Vol. 5, No. 1 We studied the effect of drought on the breeding biology of A. cingulatum at a breeding site in Florida. Specifically, we examined the annual size and structure of the adult breeding population and determined annual reproductive success (production of larvae and metamorphs). Study Area We examined the movements of A. cingulatum at Pond 73-04 in the Apalachicola National Forest, Liberty County, FL (T4S, R8W, S20). Pond 73- 04 is a shallow (< 30 cm), hydrologically-isolated, seasonally-inundated, 0.2- ha swamp with a canopy of Taxodium ascendens Brongn. (pond cypress), Nyssa biflora Walt. (blackgum), and Ilex myrtifolia Walt. (myrtle-leaved holly). The groundcover of the pond is dominated by graminoids including Rhynchospora inundata (Oakes) Fern. (beakrush), Panicum rigidulum Bosc ex Nees (panic grass), Aristida palustris (Chapman) Vasey (three-awn grass), Eriocaulon compressum Lam. (hatpins), and the sedges Carex glaucescens Ell. and Carex verrucosa Muhl. The pond is bordered to the north, east, and southeast by a wiregrass-dominated savanna that grades into longleaf pinewiregrass savanna. In 1960, the US Forest Service (USFS) hand-planted Pinus elliottii Engelm. (slash pine) adjacent to the west and southwest side of the pond. Historically, the slash pine plantation was a graminaceous savanna with scattered longleaf pine. The savanna and plantation were prescribe-burned in the dormant season 12 times since 1967 (D. Farnsworth, USFS, Bristol, FL, pers. comm.). Four other isolated swamps occur within 500 m of pond 73-04, but it is not known if they are used for breeding by A. cingulatum. The Florida panhandle experienced drought conditions due to three consecutive years of below average rainfall. Average annual rainfall for Wewahitchka, FL (12.5 km west of our study site) is 160.6 cm. In 1999, 2000, and 2001, rainfall at Wewahitchka was 18.7, 56.7, and 18.7 cm below average, respectively. Rainfall data for Wewahitchka in 2002 are incomplete; however, rainfall at Apalachicola (41.5 km south) was 9.7 cm above average. October–December rainfall totals for Wewahitchka were 3.9, 6.2, and 15.5 cm below normal in 1999, 2000, and 2001, respectively. In 2002, however, October–December rainfall at Wewahitchka was 38.4 cm above average (Northwest Florida Water Management District 2005). Methods Drift fence monitoring Ambystoma cingulatum movements into and out of pond 73-04 were monitored from 1999–2002 with funnel traps set along a pond-encircling drift fence. Prior to construction of the drift fence, we cleared a 0.5-m wide path through the graminaceous vegetation surrounding the pond. We constructed the 46-cm high drift fence from 61-cm wide aluminum flashing. The bottom 15 cm of the fence was buried in the soil to prevent animals from burrowing beneath. The fence was 250 m long and averaged 5 m from the pond edge (as defined by obligate wetland vegetation). Animals were 2006 J.G. Palis, M.J. Aresco, and S. Kilpatrick 3 captured in 84-cm-long x 20-cm-wide aluminum window screen funnel traps having dual interior funnel openings 5 cm in diameter (Enge 1997). We placed 23 pairs of traps at approximately 11-m intervals against both sides of the drift fence (46 traps total). Each trap contained a moistened 5- x 10-cm sponge and was shaded by a 40.5-cm square of tempered masonite. Because A. cingulatum breeding migrations coincide with rainfall (Palis 1997a), we opened traps prior to predicted precipitation and closed them when conditions conducive to amphibian movement ended (i.e., number of amphibian captures sharply declined). In 2000–2001, we opened traps a minimum of 20 days per month, during dry as well as wet weather, to increase our opportunity to capture more species. We checked traps daily when they were open. Before initiation of the study and between trapping periods (i.e., May– September), we opened eight, 1-m-long gaps in the drift fence to permit movement of animals into and out of the pond basin. Prior to trapping in 2000, 2001, and 2002, we re-cleared vegetation up to 0.25 m from both sides of the fence. We trapped from 4 October 1999 to 4 May 2000, 4 October 2000 to 15 February 2001, 5 October 2001 to 12 April 2002, and 15 October to 20 December 2002. Trapping into May 2000 and April 2002 allowed us to sample for emigrating A. cingulatum metamorphs. We recorded water depth at a gauge set in the deepest portion of the basin to track hydroperiod, and we recorded rainfall in a rain gauge adjacent to the pond. Each A. cingulatum was measured to the nearest mm with a plastic rule (snout-vent length [SVL]: tip of snout to posterior edge of vent), weighed to the nearest 0.01 g on a portable electronic balance, and marked with a unique combination of toe clips before being released on the opposite side of the fence. When available, we used natural deformities in place of toe-clipping. Scissors were dipped in isopropyl alcohol between each use. Because toeclips sometimes regenerate (Semlitsch 1987), we also marked animals with a bio-compatible fluorescent elastomer (Northwest Marine Technology, Inc., Shaw Island, WA) in 2000–2001 and 2001–2002. We injected the elastomer just beneath the skin of the legs or the abdomen at the insertion of the legs of A. cingulatum following anaesthetization with tricane methanosulfunate (MS-222). We also determined the sex of each animal (presence of a swollen cloaca indicated a male). Larval sampling In addition to sampling for A. cingulatum metamorphs at the drift fence, we looked for evidence of reproductive success by sampling for late-stage larvae. We searched for larvae by dipnetting through inundated herbaceous vegetation with a 4-mm mesh dipnet in March 2002 and in February and March 2003. Dipnetting all appropriate microhabitats for A. cingulatum larvae in February or March is an established means to determine presence or absence of this species (Bishop et al., 2006, Palis 1997b). In addition to our efforts, personnel of the Florida Fish and Wildlife Conservation Commission (FWC) dipnetted the site using the same technique during statewide A. cingulatum surveys (March 2001–2003; D. Cook and M. Wilson, FWC, Tallahassee, FL, pers. comm.). 4 Southeastern Naturalist Vol. 5, No. 1 Data analysis We computed the number of A. cingulatum captured (excluding recaptures) per rainy night during the October–December migration period for each year. We also compared October–December rainfall totals at our study site among years using a Chi-square goodness of fit test. We omitted the single female captured in both 1999–2000 and 2000– 2001 from the following analyses. We used a Chi-square test to determine if the ratio of males to females differed from parity in 1999–2000, the only season during which sample sizes were sufficiently large to permit statistical testing. For all four years combined, we used a t-test to compare SVL of males and females and ANCOVA (controlling for SVL) to compare initial capture mass of males with gravid females and non-gravid/spent females. For non-gravid/spent females we used the initial capture weight of nongravid females and recapture weight of spent females; multiple recaptured spent females were not included in this analysis. Results We captured 30 A. cingulatum during or following rainfall at the drift fence from 1999–2002; 21 in 1999–2000, six in 2000–2001 (including a recapture from 1999–2000), three in 2001–2002, and one in fall 2002. The capture rate of migrants during October–December declined from 1.9 salamanders per rainy night in 1999, to 0.4 in 2000, 0.15 in 2001, and 0.1 in 2002 (Fig. 1). We did not capture any metamorphs. The sex ratio (9M:12F) of immigrating adults did not differ from parity in 1999–2000 (χ2 = 0.43, df = 1, P = 0.5). We captured too few animals in 2000–2001 (2M:4F), 2001–2002 (1M:2F), and fall 2002 (1M) to statistically examine sex ratio. Females were slightly longer (SVL; 59.4 ± 6.9 mm; mean ± 1 SD) than males (54.3 ± 6.5 mm; t = -2.02, df = 27, P = 0.05). The mass of males (4.4 ± 1.1 g) and nongravid/spent females (3.9 ± 1.3 g) did not differ (F1,18 = 1.93, P = 0.182); however, the mass of gravid females (8.0 ± 2.5 g) was greater than that of males (F1,20 = 9.56, P = 0.006). Figure 1. Number of Ambystoma cingulatum and amount of rainfall from October–December 1999, 2000, 2001, and 2002 at Pond 73- 04, Apalachicola National Forest, Liberty County, FL. 2006 J.G. Palis, M.J. Aresco, and S. Kilpatrick 5 The SVL of A. cingulatum increased during the first three years of this study. Salamanders (males and females combined) captured in 1999–2000 averaged 55 mm SVL (range = 42–64), whereas those captured in 2000– 2001 averaged 61 mm (range = 56–68), and those captured in 2001–2002 averaged 68 mm (range = 64–71). The single male captured in fall 2002 was 44 mm SVL. This individual’s size and emaciated appearance suggested it was a yearling (Palis 1997a). We captured only one individual, a female, in successive years. When first captured (1999), this individual was 53 mm SVL, weighed 2.5 g, and was not gravid. The following year (2000), she was 61 mm SVL, weighed 6.0 g, and was gravid. Total rainfall from October through December varied significantly among years (χ2 = 34.28, df = 3, P < 0.001). More rain fell in fall 1999 (222.9 mm) and fall 2002 (229.0 mm) than in fall 2000 (138.2 mm) or fall 2001 (156.0 mm). The pond filled and dried four times between December 1999 and May 2000, was dry from December 2000 to late February 2001, held water from early January to mid-April 2002, and held water from mid- October 2002 through at least March 2003. Neither we nor FWC personnel captured larvae during dipnet surveys. Discussion During the 4-year study period, the number of A. cingulatum entering Pond 73-04 to breed dropped from 21 to one. The decline in the number of A. cingulatum migrating to pond 73-04 in 2000 and 2001 may have been due to insufficient rainfall. October–December rainfall totals at pond 73-04 in 2000 and 2001 were 84.7 mm and 66.9 mm less, respectively, than the same period in 1999. Furthermore, October–December rainfall totals at Wewahitchka were 62.2 mm and 155.2 mm below average in 2000 and 2001, respectively. Like other southeastern coastal plain amphibians (Semlitsch et al. 1996), A. cingulatum may not migrate to breeding sites during breeding seasons with abnormally low rainfall. We expected an increase in the number of immigrants in fall 2002, when October–December rainfall at pond 73-04 was 6.1mm, 90.8 mm, and 73.0 mm higher than 1999, 2000, and 2001, respectively. Contrary to our expectation, we captured only one immigrant in fall 2002. This apparent lack of stimulation to initiate migration of large numbers of A. cingulatum to Pond 73-04 in fall 2002 suggests that movement is not simply a matter of sufficient rainfall during the breeding season. Other factors, including cumulative rainfall during the year or over a period of years, adult pond fidelity, juvenile recruitment, and adult attrition could have influenced the size of the fall 2002 breeding population. Due to several years of reduced rainfall (cumulative rainfall deficit of 94.0 cm from 1999–2001 at Wewahitchka), the moisture threshold for movement of most A. cingulatum may not have been met in fall 2002 despite receiving slightly more rain in fall 2002 than fall 1999, the year when 21 immigrants were captured. Other than the proximate cues of rainfall and 6 Southeastern Naturalist Vol. 5, No. 1 temperature (Palis 1997a), nothing is known regarding the environmental cues used by A. cingulatum to initiate migration to breeding sites. Further, several years of below-normal rainfall could have reduced feeding opportunities resulting in the lack of acquisition of energy reserves required for reproductive activity (Semlitsch et al. 1996). The reduction in the number of A. cingulatum migrating to Pond 73-04 to breed may have also been due to abandonment of this site for other nearby wetlands. Although we cannot discount this possibility based on our data, we believe this scenario is unlikely for the following reasons. First, adults of other ambystomatids are typically philopatric, returning to the same site to breed in multiple years (Blackwell et al. 2003, Raymond and Hardy 1990, Semlitsch et al. 1993, Vasconcelos and Calhoun 2004), even those that have been destroyed (Pechmann et al. 2001, Shoop 1968). Breeding-site fidelity has also been observed in A. cingulatum (Palis 1997a). However, the number of identifiable recaptures in that study was low due to the high frequency of natural toe deformities which reduced effectiveness of toe-clipping as a means of identifying individuals between years (J.G. Palis, unpubl. data). Second, we have no evidence that the wetlands within 500 m of pond 73-04 had significantly different hydrologic regimes from those observed at Pond 73-04. In fact, hydrologic regimes similar to that of Pond 73-04 were observed in known/potential A. cingulatum breeding sites across much of the Florida panhandle during the drought (J.G. Palis, unpubl. data; D. Bishop, Virginia Polytechnic Institute and State University, Blacksburg, VA, pers. comm.; K. Enge, FWC, Quincy, FL, pers. comm.; D. Printiss, The Nature Conservancy, Bristol, FL, pers. comm.). Therefore, we see no compelling reason for adult A. cingulatum to abandon Pond 73-04 for nearby wetlands. The reduction in the breeding population may also have resulted from the lack of juvenile recruitment into the population during the study period. We did not detect A. cingulatum larvae or metamorphs at Pond 73-04 during the study. Lack of juvenile recruitment in amphibians is often followed by a reduction in the size of the adult breeding population (Berven 1990, Semlitsch et al. 1996, Sjogren 1991). Coincident with the lack of recruitment into amphibian breeding populations is an increase in body size of adults (Dodd 1993, Richter and Seigel 2002). We observed such an increase in adult body size, suggesting an aging population (Richter and Seigel 2002). Although the lifespan of A. cingulatum in the wild is unknown, captives have lived no more than four years (Palis and Means 2005). If the lifespan of A. cingulatum in the wild is comparable to that in captivity, droughts lasting ≥ 4 years could potentially have negative consequences for A. cingulatum populations. After at least three consecutive years of apparent reproductive failure, the number of A. cingulatum migrating to Pond 73-04 declined precipitously. Whether the decline continued after the termination of this study or was of sufficient magnitude to cause the extirpation of the population that breeds at Pond 73-04 is unknown. Studies of longer duration are needed to address these questions, as well as to separate such environmentally induced population declines from human-caused population declines. Nonetheless, 2006 J.G. Palis, M.J. Aresco, and S. Kilpatrick 7 our observations suggest that protection of clusters of A. cingulatum breeding sites, especially those with different hydrologic regimes, is necessary to guard against population declines at any one breeding site resulting from stochastic events such as drought. Acknowledgments We gratefully acknowledge funding provided by the US Fish and Wildlife Service (USFWS; L. LaClaire) and The National Council for Air and Stream Improvement (T.B. Wigley). We thank the following individuals who contributed to the success of this study: G. Anglin, W. Baker, A. Colaninno, D. Cook, D. Farnsworth, F. Fulford, M. Gunzburger, S. Johnson, L. Kirn, L. Morgan, T. Ostertag, D. Printiss, C. Rankin, J. Ruhl, C. Sterrett, K. Studenroth, B. Wigley, M. Wilson, and the Liberty Wilderness Crossroads Camp Crew. We also thank S. Richter and two anonymous reviewers for comments that improved this manuscript. Our study was authorized by a US Forest Service Special Use Permit, USFWS permit TE008077-1, and FWC permit WV99431. J.G. Palis dedicates this manuscript to the memory of his late father, Leonard. Literature Cited Anderson, J.D., and G.K. Williamson. 1976. Terrestrial mode of reproduction in Ambystoma cingulatum. Herpetologica 32:214–221. Berven, K.A. 1990. Factors affecting population fluctuations in larval and adult stages of the Wood Frog (Rana sylvatica). Ecology 71:1599–1608. Bishop, D.C., J.G. Palis, K.M. Enge, D.J. Printiss, and D.J. Stevenson. 2006.Capture rate, body size, and survey recommendations for larval Flatwoods Salamanders (Ambystoma cingulatum). Southeastern Naturalist 5(1):9–16. Blackwell, E.A., R.A. Angus, G.R. Cline, and K.R. Marion. 2003. Natural growth rates of Ambystoma maculatum in Alabama. 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