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Herpetofaunal Inventory of Wormsloe State Historic Site, Savannah, Georgia
Nancy K. O’Hare and Marguerite Madden

Southeastern Naturalist, Volume 17, Issue 1 (2018): 1–18

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Southeastern Naturalist 1 N.K. O’Hare and M. Madden 22001188 SOUTHEASTERN NATURALIST Vol1.7 1(71,) :N1–o1. 81 Herpetofaunal Inventory of Wormsloe State Historic Site, Savannah, Georgia Nancy K. O’Hare1,* and Marguerite Madden2 Abstract – There is renewed interest in inventory and monitoring projects, due in part to mandates to evaluate the effects of surrounding development and climate change on the biotic communities of public lands. We inventoried an understudied area, Wormsloe State Historic Site, near Savannah, GA. We directly observed or trapped 21 herpetofaunal (i.e., amphibian and reptile) species. Chao estimates predicted that less than 1 additional amphibian species and 3–4 additional reptile species might occur with further trapping. Most species had low abundance: less than 10 individuals for 75% of species. Species richness on Wormsloe was about ⅓ that recorded on the adjacent mainland (less than 1 km distance). Some species not detected required specific habitats lacking at Wormsloe. Other undetected species may have been extirpated by past land-uses. Also, the changing landscape context, caused by development of surrounding areas, has likely diminished both landscape connectivity and available freshwater, shortening the hydroperiod of breeding ponds. Of import to breeding amphibians, each of the depressions on Wormsloe has a drainage ditch connecting it to salt-water tides but the water-control structures preventing tidal flux are no longer in place. Resources management can improve amphibian breeding habitat simply by eliminating tidal influxes along drainage ditches. Maintaining existing populations of common species should be a priority for all public lands. Introduction Federal mandates to assess the effect of projected climate variability on species distribution and abundance on public lands have revived inventory and monitoring activities on many conservation lands (Byrne 2007, Daszak et al. 2005, McMenamin et al. 2008). These assessments require recent data on distribution and natural variation of abundances. In the Georgia Sea Islands region, knowledge of the explicit spatial distribution of herpetofauna relies primarily on museum specimens (Williamson and Moulis 1979, 1994) supplemented by incidental observations and limited surveys (Laerm et al. 2000, Shoop and Ruckdeshcel 2003). However, many of the observations from these museum specimens were made more than 25 years ago, in a region that has experienced significant regional development. The National Park Service (NPS) recently instituted annual vocal surveys for amphibians on their lands, but similar efforts are lacking for state and private lands. Moreover, knowledge of species distribution is unequal; there is more information for the larger, outer barrier islands, and less information for the inner, smaller marsh islands. Overall, recent 1Center for Geospatial Research, Department of Geography, University of Georgia, Athens, GA 30602. 2Center for Geospatial Research, Department of Geography, University of Georgia, Athens, GA 30602. Corresponding author - nancyohare@gmail.com. Manuscript Editor: John Placyk Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 2 estimates of herpetofaunal distributions and abundances in many of the conservation areas in the Georgia Sea Islands region are either incomplete or outdated. Recent initiatives of amphibian inventory or monitoring on federal lands have added data for 4 conservation areas in the region, including Harris Neck National Wildlife Refuge (Dodd and Barichivich 2007), Fort Frederica National Monument on St. Simon’s Island (Byrne et al. 2010a), Fort Pulaski on Cockspur Island (Byrne at al. 2011), and Cumberland Island National Seashore (Byrne et al. 2010b). Similar efforts for inventory and monitoring of herpetofauna within the many state or private conservation lands in the region, however, seem lacking and much remains unknown about current species distributions. Recent information on species distribution from individual conservation areas is imperative to resource-management planning. A number of conservation areas in the region may have experienced indirect impacts in the past 25 years from external influences that threaten internal management effectiveness (Kushlan 1987). Both increased industrial water usage,—e.g., paper mills in Brunswick, GA, affecting Sapelo Island—and the increase in impervious-surface area from development along the Georgia coast have altered ground-water recharge (O’Driscoll et al. 2010, Stringfield 1964). Species may persist in developed areas for years before eventual extirpation (Gagne and Fahrig 2010), which may render older surveys inadequate for future planning. Two previous studies integrated available information on herpetofaunal distribution to investigate biogeography of the Georgia Sea Islands (Laerm et al. 2000, Shoop and Ruckdeshcel 2003). However, both studies overlooked significant physical geographical factors, land-use history, and species-specific life-history traits likely to influence amphibian diversity on islands in the region. This study provides a herpetofaunal inventory from an understudied conservation area, Wormsloe State Historic Site, and places it within the context of its land-use history and the changing landscape of the region. Methods The Georgia Sea Islands region includes ~577 islands >1 ha (2.54 ac), with an additional ~700 islands less than 1 ha, but >0.5 ha. These islands are separated by rivers and tidal marsh; about 70 islands are named. Within the Georgia Sea Islands region, ~76,000 ha of land and tidal marshes are protected in 42 discrete units either privately (6), or at the county (1), state (24), or federal (11) level. Wormsloe State Historic Site (hereafter, Wormsloe), located on the Isle of Hope ~8 km southeast of Savannah, GA, was established in 1979 and is presently managed by the Georgia Department of Natural Resources (Fig. 1). Land conservation at Wormsloe, under the aegis of the Barrow family, predates establishment of the state historic site and extends back more than 100 years (Bragg 1999). Wormsloe encompasses 796 ha, of which 371 ha are uplands split among 3 islands. The largest upland portion (306 ha) is located on the southern end of the Isle of Hope (629 ha), the northern end of which is residential, primarily single-family homes, at a density of 4–12.5 units/ha. The other 2 upland islands (Long Island, 49 ha; Pigeon Island, Southeastern Naturalist 3 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 Figure 1. Location of Wormsloe State Historic Site and of trap sites within Wormsloe. General landcover types from the 2011 Georgia DNR vegetation map are included. Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 4 16 ha) have no current development, and access to them is limited. The remaining 425 ha of Wormsloe are the tidal marshes and creeks separating the islands. Ground elevation on the islands ranges between sea level and 4.5 m (NAVD 1988). All freshwater sources are seasonal and dependent upon rainfall; the site has no freshwater streams or dredged ponds (Georgia Department Natural Resources 2010). We conducted trapping near seasonal ponds because many adult amphibians (e.g., most frogs and toads, some salamanders) seasonally concentrate in these microhabitat features to breed, and there is a subsequent pulse of metamorphs that disperse from the natal sites. To detect natural depressions that might be seasonally inundated, we obtained a digital elevation model (DEM) of the island from Chatham County, GA. The DEM was derived from lidar data collected in 2010 and had a 95% confidence interval for vertical accuracy of 36 cm and horizontal accuracy of 72 cm. We visited depressions identified on the DEM to verify field indicators of hydrology and select trapping sites. We visited each of the 16 depressions identified from the DEM and selected 5 sites for trapping based upon their field indications of recent hydrology and location at lower ground elevations (i.e., those sites most likely to have longest seasonal ponding; see Fig. 1). Long Island and Pigeon Island had only 2–3 potential seasonal ponds and were not included in sampling. Drainage ditches were also evident on the DEM. As the study progressed, the importance of drainage ditches became evident when we directly observed saltwater tidal inundation reaching more than 300 m inland via the canals. We used heads-up digitizing in ArcGIS 10.2 to create a line file of the drainage ditches and verified in the field ditch width, depth, and steepness of sides. Each sampling site included 1 drift-fence–trap array for terrestrial fauna and 50 PVC pipes for treefrogs. Drift-fence arrays had three 10-m–long arms (Enge 2001). We installed 3 hardware-mesh funnel-traps on each of the 3 arms of the array (9 traps total). We placed 2 traps with a funnel at either end on either side of the fencing material mid-way along the length of arm, and 1 trap at the end of each arm, with a funnel on either side of the fencing material. We constructed all traps from 3-mm–mesh hardware cloth. In addition to the funnel traps, there was also a single pitfall-trap at the center. We operated drift-fence arrays between May and August 2011 (29 check-days), early March 2012 (3 check-days), May and June 2012 (17 check-days), mid-March 2013 (4 check-days), and late July/early August 2013 (3 check-days). Time between check days varied from 1 to 3 days in 2011 and 2012; in 2013, University of Georgia permit protocols were changed to require daily trap-checks. We did not operate traps during cooler winter periods when many amphibian species are less active and seasonal ponds were dry, and we trapped only for short periods during the summer when high daytime temperature (>30 °C) increased mortality and seasonal ponds were also dry. Providing shallow water or moist sponges in the traps decreased direct mortality, but also resulted in other animals vandalizing and destroying traps to get at the fresh water. PVC-pipe refugia trapped arboreal treefrogs (Boughton et al. 2000). We cut PVC pipes to ~75-cm lengths fitted with a single endcap. We mounted 50 PVC pipes on trees at each site—25 each of 2 diameters: 2.5 cm and 3.75 cm. The pipe bottoms were Southeastern Naturalist 5 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 ~2 m above the ground surface. We checked PVC refugia quarterly (March, June, September, December) from March 2011 to December 2014. For all captured amphibians and reptiles, we determined snout–vent length and total length to the nearest 0.1 mm using digital calipers, weight to the nearest gram, and gender if possible. Specimens were then released near the capture site. All measurements at Wormsloe were taken by the same person. The body size of insular Anaxyrus terrestris (Southern Toad) in the southeastern coastal plain region has been described both as larger than on the mainland (Sanders 1961, Smith and List 1955) as well as smaller than on the mainland (Duellman and Schwartz 1958). Consequently, we compared Southern Toad body size at Wormsloe to a mainland population at the University of Georgia Savannah River Ecology Lab (http://srel.uga.edu/), located 200 km to the northwest on mainland Georgia; mainland data were collected in 2010 and 2011, which partially overlapped this study. Herpetofauna persisting at Wormsloe likely occurred there before significant anthropogenic impact. Wormsloe has an extensive land-use history, even though at present the site appears natural. Past land uses included land clearing for agriculture, logging, and dredging of drainage canals. To determine the extent of past land-use, we obtained historical maps of land use and landcover of the Isle of Hope from 1897, 1908, and 1927 from the DeRenne Family Collection housed at the University of Georgia Hargrett Library (Athens, GA). We geo-rectified in ArcGIS 10.2 digital images of the historical maps with estimated horizontal accuracy of ~5–10 m. We digitized landcover from these maps for use in subsequent analyses. The area around Wormsloe is primarily developed, which may disrupt metapopulation dynamics by reducing suitable wetland breeding habitats. To assess the development around Wormsloe, we downloaded Georgia Land Use Trends (GLUT) landcover maps from 1978 and 2008 from Georgia GIS Clearinghouse (http://data.geospatial.org). Both of these landcover maps were derived from Landsat satellite image data and national landcover data sets and used a classification scheme similar to the US Geological Survey Anderson Level II (Anderson et al. 1976). The 1978 map had a pixel size of 60 m, whereas the 2008 map had 30-m pixel size. We calculated the percentage of area classified as developed in a 1-km, 2.5-km, and 5-km buffer around Wormsloe. We selected these distances because they are representative of amphibian dispersal distances (Smith and Green 2005). We captured some reptiles, but abundances were generally low; the selected dispersal distances would also be typical for the most abundant reptiles captured (e.g. smaller lizards). To provide a general context for weather during the trapping period, we obtained daily rainfall data from the station at Savannah International Airport, ~20 km northnorthwest from the study area. This station has the longest period of record in the region—1948 to present. We conducted all mapping and geospatial figure generation in ArcGIS 10.2, and performed statistical analyses and created histograms, scatterplots, and box-andwhisker plots in Statistica 12 (StatSoft 2014). The box-and-whisker plots of mean Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 6 (point), standard error (box), and standard error multiplied by 1.96 (whiskers) can be visually interpreted for statistical significance; if the whiskers of the plots did not overlap, then the means were significantly different. Due to sample-size differences, we employed non-parametric Mann-Whitney U tests to determine significant differences between means. We estimated total species richness from the sample data with Chao’s non-parametric estimates based upon low numbers in most classes (Chao 1984) in the freeware EstimateS (Colwell and Elsensohn 2014). Extrapolation, to estimate species richness if 2500 individuals were captured, randomized capture data for 50 iterations to minimize the effect of order of captures, and used Chao’s original formula. Results Average annual rainfall for the study area is 130 cm. During the trapping years of 2011, 2012, and 2013, annual rainfall levels were lower than average (85 cm, 90 cm, and 110 cm respectively). We trapped a cumulative total of 1135 individuals of 19 species in drift fences (Table 1). We trapped less than 10 individuals of 14 of the 19 species on 10 or fewer of the total number of check days, indicating no pulses of individuals for most species. Two amphibian species accounted for 86% (n = 997) of all individuals trapped, with nearly half of these (443) captured on a single night. Chao estimates of maximum species richness were extrapolated to 2500 individuals. To determine the impact of the single date that accounted for 40% percent of all individuals captured, we compared species richness estimates for all dates to estimates that excluded this single night. Maximum predicted species richness at 2500 individuals was 22.2 for all dates, compared to 23.0 if the single night was excluded, suggesting that the activity pulse had minimal impact on the final estimates. We then calculated separate curves for amphibians and reptiles using captures from all dates (Fig. 2). These curves suggested that any new species trapped would more likely be reptiles (~4 species if 500 individuals trapped) than amphibians (add less than 1 species if 2500 individuals trapped). Species richness and captures were unequal between sites (Table 2). Four of the 19 species occurred at all trap sites; 6 species occurred at only 1 site. As noted above, there was a pulse of 443 individuals on 4 March 2012; the following night was also very rainy with similar temperatures, but we captured only 15 individuals. The 4 March pulse of individuals was restricted to 2 species, Southern Toad (total n = 191) and Scaphiopus holbrookii (Eastern Spadefoot Toad) (total n = 215), with each dominant at a different site. Southern Toad was more abundant at Birdy (n = 128), while Eastern Spadefoot Toad was more common at Bent Tree (n = 201). We captured each of these species at the sites on other nights, and they were among the 4 species captured at all sites. We checked PVC-pipe refugia 12 times from July 2011 to December 2013, and recorded a total of 125 individuals of 3 species (see Table 1). We documented all 3 species during the first check, and Chao’s estimates of species richness extrapolated to 500 individuals did not predict additional species (Fig. 3). These 3 species had Southeastern Naturalist 7 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 Table 1. Summary of captures in 5 drift-fence–trap arrays, PVC-pipe refugia, and incidental observations. n = number of individuals. Scientific name Common name Sites Dates n Drift Fencing Trapping Acris gryllus (Le Conte) Southern Cricket Frog 3 2 4 Anaxyrus terrestris Bonaterre Southern Toad 5 39 613 Gastrophryne carolinensis (Holbrook) Eastern Narrow-mouthed Toad 4 13 45 Hyla cinerea Schneider Green Treefrog 4 3 4 Hyla squirella Bosc Squirrel Treefrog 2 4 6 Lithobates sphenocephalus (Cope) Southern Leopard Frog 1 1 1 Scaphiopus holbrookii (Harlan) Eastern Spadefoot 5 14 364 Plethodon glutinosus (Green) complex Slimy Salamander 3 3 7 Kinosternon subrubrum (Bonnaterre) Eastern Mud Turtle 2 2 2 Terrapene carolina (L.) Eastern Box Turtle 1 1 1 Anolis carolinensis Voight Green Anole 3 8 9 Eumeces fasciatus L. Common Five-lined Skink 1 1 1 Eumeces inexpectatus (Taylor) Southeastern Five-lined Skink 1 1 1 Eumeces laticeps (Schneider) Broad-headed Skink 5 17 33 Scincella lateralis (Say) Little Brown Skink 5 12 26 Agkistrodon contortrix (L.) Copperhead 2 5 5 Cemophora coccinea (Blumenbach) Scarletsnake 1 1 1 Coluber c. constrictor L. Northern black racer 4 8 10 Thamnophis sirtalis (L.) Common gartersnake 1 2 2 Amphibians 8 species 5 41 1044 Reptiles 11 species 5 11 91 PVC-Pipe Refugia Hyla cinerea (Schneider) Green Treefrog 9 12 Hyla femoralis Bosc Pine Woods Treefrog 11 36 Hyla squirella Bosc Squirrel Treefrog 12 77 Totals 3 species 12 125 Incidental Observations Chelydra serpentina (L.) Common Snapping Turtle 1 1 Cumulative totals all methods (number of species) Amphibians 9 Reptiles 12 All herpetofauna 21 Table 2. Captures in drift-fence–traps by site. Captures of Southern Toad and Eastern Spadefoot on the night of 4 March 2012 given in parentheses. Amphibians Reptiles Site Dates Species Individuals Dates Species Individuals BentTree 27 5 329 (215) 16 8 23 Birdy 26 5 425 (191) 10 5 13 Palmglade 20 7 64 (5) 12 4 16 VP3 25 3 147 (35) 12 6 20 Yanxi 16 7 79 (0) 13 3 19 Total 41 8 1044 (443) 32 11 91 Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 8 Figure 2. Chao estimates of species richness extrapolated from drift-fence–trap data. Top: All amphibians and reptiles. Middle: Amphibians only. Bottom: Reptiles only. Southeastern Naturalist 9 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 a high frequency of occurrence (75–100% of check dates); their abundances were more variable than frequency of occurrence. Both sampling methods and incidental observations detected 21 species of amphibians and reptiles at Wormsloe: 8 anurans, 1 salamander, 3 turtles, 5 lizards, and 4 snakes. Only 2 species, the treefrog Hyla femoralis (Pine Woods Treefrog) and the turtle Chelydra serpentina (Common Snapping Turtle), were not sampled by driftfence arrays. Pine Woods Treefrog was the most common species detected in PVCpipe refugia. Incidental observations added Common Snapping Turtle . Southern Toad and Eastern Spadefoot Toad were the only amphibians observed amplectant (attempting to breed). On 2 separate dates, we observed multiple amplectant pairs in the water as well as hopping in and out of the water on to dry surfaces while still amplectant. No egg masses were laid despite direct observation of amplectant pairs in the water, nor did we find egg masses the following day, prompting us to test water salinity, which we found was 5 ppt. To determine if this water salinity level was typical, we conducted monthly salinity tests of the surficial water or of the surficial soil if the sites were dry. More importantly, we detected no egg masses of any species in natural depressions at Wormsloe in 2011, 2012, or 2013. Direct observations of amplectant toads that failed to lay egg masses, lack of any egg masses during 3 springs, and field measurements of brackish water in depressions (O’Hare 2015) suggested that water salinity caused by monthly to bi-weekly tidal intrusion along drainage ditches was limiting egg laying. We did Figure 3. Chao estimates extrapolated from PVC-pipe–refugia cap tures of treefrogs. Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 10 not begin the research with the expectation that tidal waters were influencing inland freshwater resources. Southern Toad did breed annually in an artificial water garden. We summarized body-size metrics of species with more than 5 individuals captured (Table 3). We conducted additional analyses for the most common species, Southern Toad, to compare sizes of our Wormsloe sample to those from a mainland site. The average size of Southern Toads at Wormsloe was 47.2 ± 0.6 cm SE, with no significant differences in size between females (47.2 ± 0.5 cm; n = 207) and males (46.9 ± 0.3 cm; n = 336; Mann-Whitney U = 33433, Z = 0.756, P = 0.449). On the mainland, average size was 61.6 ± 0.6 cm, and females (65.6 ± 0.6 cm; n = 97) were larger than males (54.9 ± 0.7 cm; n = 57; Mann-Whitney U = 282, Z = 9.287, P less than 0.001). The average sizes of both female and male Southern Toads at Wormsloe were smaller than on the mainland (females Mann-Whitney U = 803, Z = 12.928, P > 0.001; males Mann-Whitney U = 1588, Z = 10.073, P < 0.001; Fig. 4). Landscape context Amphibian species persisting today likely had to persist through past land uses. We summarized the general context surrounding each depression from available historical maps. Although all sites are wooded today, 4 of the 5 sites were fields in 1908 and 1 site remained open field until at least 1937. In 1908, distance from depression to wooded area ranged from 0 m to 425 m. Distance from 1 depression to its nearest neighbor ranged between 75 m and 275 m. More importantly, today each of the depressions has a drainage ditch connecting it to tide-influenced waters. The presence of ditches was included on the 1897 map, but not other maps. The 1897 map only showed the northern portion of the island; in 1897, the 3 depressions included on the map each had a ditch connecting it to tidal marsh. The broader landscape context of Wormsloe has also changed, although we were only able to quantify changes from satellite imagery starting in 1974 (Table 4, Table 3. Metrics of snout–vent length (mm) for species with more than 5 captures. Data for Southern Toad from SREL provided by David Scott, SREL. Species n Mean Min Max SD Wormsloe (Island) Anaxyurus terrestris (Southern Toad) All 613 47.0 23 80 7.7 Males 336 47.0 27 74 5.9 Females 227 47.2 23 80 10.2 Gastrophryne carolinensis (Eastern Narrow-mouthed Toad) 22 31.9 20 65 12.2 Scaphiophus holbrookii (Eastern Spadefoot) 299 50.6 24 69 6.1 Hyla squirella (Squirrel Tree Frog) 21 33.5 25 42 5.1 Hyla femoralis (Pine Woods Tree Frog) 8 35.5 27 46 5.6 Hyla cinerea (Amercian Green Tree Frog) 9 52.0 41 59 5.3 SREL (Mainland) Anaxyurus terrestris (Southern Toad) All 154 61.2 46 84 7.6 Males 57 54.9 46 61 2.9 Females 97 65.6 50 84 6.7 Southeastern Naturalist 11 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 Figure 4. Histograms and box and whisker plots comparing body size of Anaxyurus terrestris (Southern Toads) between Wormsloe (a marsh island) and Savannah River Ecology Lab site (mainland). Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 12 Fig. 5). The percentage of developed land has increased in the 1-km, 2.5-km, and 5-km buffers around the site. Development occurred primarily on forested lands. In the early 1970s, construction of the Diamond Causeway, directly linking Skidaway Island to the mainland, altered tidal flux between the southern end of the Isle of Hope and Pigeon Island. Prior to construction of the Diamond Causeway, road access to Skidaway Island was via a road traversing the middle of the Isle of Hope, and partly through Wormsloe. It is still evident at Bell Point, on Wormsloe, and on Long Island. The resultant sedimentation added land between the Isle of Hope and Long Island to the east; this land is presently dominated by pine. It also increased tidal marsh in the area, at the expense of open tidal river. Discussion We trapped or observed 21 reptile (12) and amphibian (9) species at Wormlsoe. In comparison, species occurrences for Chatham County, in which Wormsloe is located, range from 74 species (24 amphibians and 50 reptiles; Williamson and Moulis 1979, 1994) to 115 species (Jensen et al. 2008). Willamson and Moulis (1979, 1994) catalogued specimens at Savannah Science Museum (Savannah GA; now held by the Georgia Southern University, Statesboro, GA). Jensen et al. (2008) relied primarily upon the 5-year Georgia Herp Atlas project, without specific references or locations for species records. Most species distributions were generalized Table 4. Landscape context of Wormsloe State Historic Site in 1974 and 2008. Area (ha) Percentage Landcover 1974 2008 1974 2008 1-km buffer Other 137 58 7% 3% Developed 142 287 8% 15% Forest 499 359 26% 19% Open water 369 314 20% 17% Tidal marsh 740 869 39% 46% Grand total 1887 1886 100% 100% 2.5-km buffer Other 514 252 9% 4% Developed 502 1391 9% 24% Forest 1976 1207 35% 21% Open water 759 668 13% 12% Tidal marsh 1950 2189 34% 38% Grand total 5702 5706 100% 100% 5-km buffer Other 997 356 7% 2% Developed 1494 3562 10% 23% Forest 4358 2674 29% 18% Open water 2048 2072 14% 14% Tidal marsh 6248 6499 41% 43% Grand total 15,144 15,163 100% 100% Southeastern Naturalist 13 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 Figure 5. Changing landscape context of Wormsloe State Historic Site. Surrounding landuse and landcover in 1974 (top) and 2008 (bottom). Dark rings are at distances of 1 km, 2.5 km, and 5 km. These distances were selected to overlap with typical dispersal distances of many amphibians. Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 14 to the county level, yet distribution of several species was restricted to the western part of the county (i.e., not on the adjacent mainland). Regardless of the source, species richness calculated based on our observations from Wormsloe was 28% (Williamson and Moulis 1979, 1994) to 19% (Jensen et al. 2008) of the species richness detected on the adjacent mainland. Given the smaller land area and lower habitat diversity (e.g., gamma diversity) compared to the mainland, lower species diversity relative to the mainland is not unexpected. Some species may not have been detected at Wormsloe for various reasons; extrapolation of trapping data to predict maximum species richness suggested that 3–4 additional reptile species and 1 amphibian species would likely be added to the species list given further trapping. Even if additional effort detected the predicted maximum species richness, overall species diversity at Wormsloe still appears to be less than ~25% of species diversity on the mainland. This finding suggests that consideration of the types of species absent from Wormsloe might be worthwhile. Some species present on the mainland or other islands are likely naturally absent from Wormsloe because it presently lacks certain micro-habitats (e.g., longer hydroperiods, freshwater streams). The low physical relief on the island makes it improbable that flowing freshwater streams ever existed at Wormsloe. Species that could have occurred if long-hydroperiod wetlands existed in the past include Siren spp. (aquatic salamanders), Amphiuma means Garden in Smith (Two-toed Amphiuma), and most Lithobates spp. (true frogs). Other species may be undetected or absent because of land-use legacies from farming or the changing landscape context. For example, because farming cleared old-growth forests and disturbed soils, salamanders that rely upon upland forested habitats may have been extirpated. Forests regrew after farming ceased, but the successional forests provided altered habitat conditions, and development of the surrounding landscape may have hindered recolonization (Barrett et al. 2010) from other islands. Furthermore, woodland salamanders avoid traversing grasslands (Rittenhouse and Semlitsch 2006), and even small, 1st-order streams effect movement (Marsh et al. 2007). Although freshwater streams are absent from the islands, the tidal creeks interspersed in the salt-marsh grasslands are analogous dispersal barriers. Consequently, the salt-marsh grasslands and the larger tidal rivers separating Wormsloe from the mainland and other islands present significant dispersal barriers for many salamanders, even though the distance (less than 250 m from mainland) is relatively short. Unexpectedly, most species had low abundance, with ≥10 individuals captured for only 6 of the 21 species. Amphibians were an order of magnitude more abundant than reptiles. Even so, abundances were skewed to a few, generalist species of mesic forests, which also include shorter-hydroperiod micro-habitats. Amphibians can have explosive population changes, so it is difficult to determine if skewed abundances in our data reflected the lower rainfall amounts over several consecutive years coinciding with the trapping period or longer-term trends. Regardless, lower rainfall is more likely to affect amphibian abundance and breeding than species presence or absence (Cayuela et al. 2012). The changing land-use context of Wormsloe affects not only meta-population dynamics, but also seasonal hydrology. Seasonal ponds usually occur where there is Southeastern Naturalist 15 N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 a sub-surface freshwater lens. However, increases in both impervious surface area and anthropogenic withdrawal from groundwater alters the ground water re-charge and consequently diminishes the below-ground freshwater lens that allows rainwater to seasonally pond on the surface (Reichard et al. 2012, Shuster et al. 2005). Although there are no hydrologic gages of either the freshwater lens or surficial water levels in the study area, there is anecdotal evidence for a decrease in both. There were numerous, small, open-pit wells associated with bootlegging-still sites located throughout the Isle of Hope that were operational in the 1920s to 1930s. These wells would have held freshwater; however, surface water was not observed in these sites during this study, but was reported at several still sites in 2008 (M. Madden, pers. observ.). Limited sampling at Wormsloe found a lack of freshwater lens within 2 m of the surface (N.K. O’Hare, unpubl. data collected in November 2013). A freshwater lens may exist deeper below the surface, but the soil between the surface and 2 m was saline. Other evidence for decreased hydrology is the presence of trees that require longer hydroperiods than we observed during our study. One site at Wormsloe had several adult Taxodium distichum (L.) Rich. (Bald Cypress) with well-developed cypress knees, but no saplings or seedlings, which also suggested shortened hydroperiod (Marois and Ewel 1983). Indeed, the site did not support freshwater hydroperiods longer than ~45 days during 2010–2014 period. The freshwater lens may have been depleted by lower than normal rainfall for 4 consecutive years; years of higher rainfall may naturally recharge the freshwater lens. The changing landscape context of Wormsloe and its effect on the ability of the remaining 21 herpetofaunal species to persist is concerning. Natural barriers have always isolated the island. Now, surrounding development reduces nearby suitable habitat and almost certainly changes groundwater recharge, and thus, is likely to increasingly limit already scare freshwater resources. Body size may predict persistence in changing landscapes (Allen 2010) or reflect habitat quality. Consequently, metrics on body size of the herpetofaunal community may be useful to guide resource management. Average body size of adult Southern Toad was 20% smaller on the Isle of Hope (48.7 mm) than on the mainland (61.2 mm), and less than reported for other islands in the Atlantic Coastal Plain (70–100 mm on Ossabaw Island, 18 km distant; J. Crawford, University of Georgia Marine Extension, Skidaway Island, pers. comm.). The low variation in body size (Fig. 4) combined with the observed limited breeding in multiple years suggests that body size at Wormsloe may reflect pulsed breeding and limited annual recruitment due to sub-optimal hydrologic conditions. Conclusions This study contributes to regional biogeographical studies. It highlights the need to consider gamma diversity (e.g., habitat diversity) as well as the influence of landuse legacies—drainage ditches connecting inland freshwater ponds to tide at this study area—in current species distribution. The persistence of some amphibian species at Wormsloe in the face of future changes is uncertain if sufficient freshwater to support their recruitment occurs only every few years. Recolonization or “rescue” Southeastern Naturalist N.K. O’Hare and M. Madden 2018 Vol. 17, No. 1 16 of populations at Wormsloe from adjacent areas is unlikely because most of the adjacent mainland and islands have been fragmented by development, increasing the isolation of Wormsloe. Eliminating tidal influxes that occur along anthropogenic canals inland up to 350 m into historically freshwater ponds may improve amphibian breeding habitat. Sustaining existing populations of common species should be a priority. The land-use history and changing landscape context at Wormsloe is also shared by many other conservation areas in the Georgia Sea Islands region; thus, our findings should be applicable elsewhere. Acknowledgments This research was supported by a 4-year Wormsloe Fellowship to N. O’Hare funded by the Wormsloe Institute for Environmental History and the University of Georgia Graduate School. Trapping complied with conditions in Georgia Department of Natural Resources permit 29-WJH-13-77, Scientific Research and Collecting Permit for Wormsloe State Historic Site, and University of Georgia Animal Use Permit A2012 060014-Y2-A1. The Wormsloe Institute for Environmental History also provided funding for trapping materials, arranged for on-site lodging, and provided a golf cart for on-island travel. 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