THE ECOLOGY OF A SANDHILLS POPULATION OF THE EASTERN NARROW-MOUTHED TOAD, GASTROPHRYNE CAROLINENSIS, DURING A DROUGHT C. Kenneth Dodd, Jr.1 ABSTRACT The eastern narrow-mouthed toad, Gastrophome carollnensis, is a common inhabitant of sandhill uplands in north-central Florida. From 1986 through 1990, I monitored a population of this species at a 0.16 ha wetland on the Katharine Ordway Preserve-Swisher Memorial Sanctuary, Putnam County, Florida. The pond held water only 14 mo during the 60-mo study. A drift fence-pitfall trap system encircled the pond basin to capture eastern narrow-mouthed toads as they entered and exited. A total of 5740 eastern narrow- mouthed toads (including recaptures) were captured despite a severe drought during the latter years of the study. In 1986 and 1988, approximately 900 eastern narrow-mouthed to*is entered the pond, but the numbers fluctuated substantially in the other years. Few multi-year recaptures were recorded, although two eastern narrow-mouthed toads were captured f6ur years after initial marking. Although eastern narrow- mouthed toads were active during all months of the year, peak activity occurred from June through September. Reproduction was successful only during the summer of 1985, and juveniles exited the pond basin through the spring of 1986. The adult population size-class structure remained consistent throughout the study, although the population size decreased. The adult sex ratio was male-biased in all years except 1990. Males were smaller than females in both snout-urostyle length (SUL) and weight, and differences were significant among years and between sexes. Drought eliminated reproduction for five years and seemed to reduce overall population size, but direct correlations between drought effects and natural stochastic variation are not yet possible. My data suggest that G. carohnensis survives long-term droughts by maintaining large populations scattered across a variety ofhabitats and because at least some individuals are opportunistic, rather than philopatric, in their choice of breeding sites. Long-term studies and manipulative field experiments will assist in answering some ofthe many questions raised by these results. l The author is a Research Zoologist, National Biological Service, Biological Science Center, 7920 NW 71 st Street Gainesville FL 32653, U.S.A., and Curator (Courtesy) ofthe Florida Museum ofNatural History, and an Associate Professor (Courtesy) with the Department of Wildlife Ecology and Conservation University of Florida DODD, C.K, JR. 1995. The ecology of a sandhills population of the eastern narrow-mouthed load, Gastrophryne carohnensis, during a drought Bull. Florida Mus. Nat. Hist, Biol. Sci. 38, PL I(1):11-41. 12 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) RESUMEN El sapo de boca angosta del Este, Gastrophryne carohnensis, es un habitante comun de las tierras altas arenosas del centro norte de Florida. Yo monitore6 una poblaci6n de esta esl,ecie entre 1986 y hasta 1990 en un humedal de 0.16 ha en la Catherine Onvay Preserve- Swisher Memorial Sanctuary, en el Condado de Putnam, Florida. EL estanque contuvo agua durante s610 14 de los 60 meses de estudio. Un sistema de reja-trampa en la cual los sapos calan, scubic6 rodeando todo el estanque con el objeto de cal,turar sapos de boca angosta del Este, a m«lida que 6stos entraban o salian del estanque. A pesar de una seven sequia que ocurri6 durante los Oltimos ailos de estudio, se captur6 un total de 5740 sapos de boca angosta del Este (incluyendo mcapturas). En 1986 y 1988, aproximadamente 900 sapos de boca angosta del Este entraron en el estanque, pero estos nOmeros fluctuaron substancialmente en los otros ahos. Aun cuando dos sapos de boca angosta del Este fueron capturados durante cuatro ailos desputs del marcaje inicial, se registraron escasas recapturas multianuales. Aunque los sapos de boca angosta del Este estuvieron activos durante todos los meses del ailo, el mdximo de actividades ocurri6 entre junio y septiembre. La reproducci6n fue exilosa sMo durante el verano de 1985, abandonando los juveniles la cuenca del estanque a lo largo de la primavera de 1986. La estructura etaria de la poblaci6n adulta permaneci6 constante a lo largo del estudio, aun cuando el tamafio poblacional disminuy6. La raz6n de sexos estuvo sesgada hacia los machos en todos los abos excepto 1990. Los machos fueron mAs pequeflos que las hembras en longitud naso-urostilar y peso, existiendo diferencias significativas entre afios y sexos. La sequia elimin6 la reproducci6n por cinco aAos, y pareci6 reducir el tamaAo general de la poblaci~ Correlaciones directas entre los efectos de la sequia y variaci6n natural estodstica no son posibles todavia. Mis datos sugieren que G. carolinensis sobrevive prolongadas sequias a travdz de la mantenci6n de grandes poblaciones repartidas a to largo de una variedad de habitats y adem~s al me:los algunos individuos son opttunistas en vez de filopitricos en la elecci6n de sus sitios reproductivos. Estudios a largo plazo y experimentos manipulativos de campo permitdn responder algunas de las muchas preguntas que surgen de estos resultados. INTRODUCTION Droughts are common in Florida (Winsberg 1990), and have been an important natural agent in selecting xeric-adapted plant species that comprise the vegetation of many Florida ecosystems, including the sandhills community of central and north-central Florida (Myers 1990). Although tree ring records are not published for Florida, core samples from cypress trees (Taxodium distichum) in other parts of the southeast suggest that droughts occur in cycles that alternate with mesic or wet periods of varying duration (Stahle et al. 1988). Many Florida animals, particularly amphibians and reptiles, were derived from xeric-adapted western forms that migrated to the Southeast prior to the mid-Pleistocene (Auffenberg and Milstead 1965; Meylan 1982; Webb 1990). Although droughts occur on a regular basis, there are no quantitative data on the responses of Florida's amphibian communities to prolonged drought. In other areas, drought suppresses reproduction in amphibians (Fitch 1956), results in the death of eggs or larvae prior to metamorphosis (Wright 1932; Tevis 1966; Heyer 1973; Shoop 1974; Seale 1982; Semlitsch 1983, 1987), and can lead to the decline or extinction of local populations (Blair 1957; Corn and Fogelman 1984; Osborne 1989). For temporary pond-breeding amphibians, drought may play an important role in population dynamics (e.g. Dodd 1993; Healy 1974; Harris et at. 1988; DODD: ECOLOGY OF SANDHILLS POPULATION OFGASTROPHRYNECAROUNENSIS 13 Semlitsch and Wilbur 1989). Drought also has been suggested as a contributing factor in the apparent worldwide decline in amphibians, particularly anurans. Temporary ponds are dispersed throughout Florida's xeric uplands. These ponds form in shallow clay-lined basins and typically fill during winter, spring, or summer rains (LaClaire and Franz 1990). Summer thunderstorms are frequent but scattered, and the often torrential rains help to maintain hydroperiod (i.e. the amount of time standing water is in a wetland). As summer progresses, sandhill ponds usually dry and remain without water through the autumn, unless rain from a tropical depression or hurricane refills them. The wet-dry cycles are not regular, however, and long periods with or without water are common. Many ponds in sandhill habitats lack fishes because they are not connected with other wetlands. In addition, an unpredictable and locally variable hydroperiod results in variability in invertebrate populations, such that predacious species may or may not colonize particular ponds. The composition and population sizes of invertebrate species are not consistent within a geographic region because of variation in local wetland hydroperiod coupled with variation in predators' abilities to colonize spatially fragmented habitats. The absence of fishes and the potential for reduced levels of invertebrate predation allow amphibians, particularly those species that do not have well developed antipredator defenses (Kats et al. 1988), to reproduce in temporary ponds (Pechmann et al. 1989; Bristow 1991; Dodd 1993). The importance of temporary ponds to a wide variety of wildlife is only beginning to be appreciated (Moler and Franz 1988; LaClaire and Franz 1990). In Florida sandhill communities, several species (e.g. Notophthalmus perstriatus, Rona capito aesopus) are obligate temporary pond breeders. Many other amphibians, however, also breed in temporary ponds. From March 1983 through February 1985, 13 anuran species bred in 10 temporary, isolated, clearwater, sandhill ponds averaging 0.1-0.3 ha on the Katharine Ordway Preserve/Swisher Memorial Sanctuary in Putnam Co., Florida (Moler and Franz 1988). Of 22 anuran species breeding in small isolated wetlands on the southeastern Coastal Plain, 10 use temporary ponds as their principal or exclusive breeding habitat (Moler and Franz 1988). In 1985, I began a 5-year study of a temporary wetland in the "high pine" uplands of north-central Florida. The objectives of the project were to measure the species richness, diversity, and dominance of the community (Dodd 1992) and to gather basic information on the population biology of species that use the pond and adjacent uplands. However, a prolonged drought during the study provided the opportunity to examine the effects of drought on the amphibian community. In this paper, I report the results from data gathered on the eastern narrow- mouthed toad, Gastrophgne carolinensis, the most abundant amphibian that visited the pond. This toad is found from the Delmarva Peninsula south throughout Florida and west to Missouri and Texas (Conant and Collins 1991). The species is largely subterranean and secretive in habits, and its diet consists 14 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) almost entirely of ants and termites (Holman and Campbell 1958; Ashton and Ashton 1985). Breeding occurs in a wide variety of temporary water habitats, including ponds, ditches, and pools. Although commonly found in the Florida sandhills (Campbell and Christman 1982; Mushinsky 1985), Gastrophryne occurs in many other habitat types (Carr 1940; Anderson 1954). Despite its large range and conspicuous nature during the breeding season, there have been few studies of its ecology (Wright 1932; Anderson 1954) or even of the timing of various activities, including reproductive phenophase (sensu Mitchell 1979; Trauth et al. 1990). In other parts of the Southeast, data consist mostly of observations on numbers at breeding ponds taken incidentally to other studies (e.g. Gibbons and Bennett 1974; Gibbons and Semlitsch 1982, 1991) or of anecdotal information on distribution, calling, coloration and feeding (Hecht and Matalas 1946; Duellman and Schwartz 1958; Nelson 1972; Dalrymple 1988). This paper presents data on the ecology of a Florida sandhills eastern narrow- mouthed toad population and its response to a prolonged drought. These results will form the baseline data for monitoring this population as part of a planned long-term assessment of amphibian status. ACKNOWLEDGMENTS I thank R. Altig M Crump, D. Forester, R. Franz, J. Palis and J.H.K Pechmann for reviewing drafts ofthe manuscript and offering helpful suggestions. B. Charest, K Enge, J. Stuart M. Blouin, K. Studenroth, and R. Burke assisted in data collection. I especially thank R. Franz for advice and shared information over the years and L. LaCiaire and L Smith for information on the vegetation and physical structure of Breezeway Pond. STUDY AREA AND METHODS Field data were collected at Breezeway Pond, a 0.16 ha depression marsh (Florida Natural Areas Inventory 1990) located in a shallow 1.3 ha basin on the Katharine Ordway Preserve/ Swisher Memorial Sanctumy, Putnam Co., Florida. The pond is surrounded by a "high pine" community dominated by longleaf pine (Pinus palustris), turkey oak (Quercus laevis), and ~regrass (Aristida stricta) to the south and west, a maidencane (Panicum hemitomon) meadow to the east, and a xeric oak hammock dominated by sand live oak (Q. geminata) and laurel oak (Q. hemisphaerica) to tlie north. Breezeway Pond is formed in a shallow sinkhole depression and is not part of a now-through drainage system. Water enters the pond solely from rainfall and groundwater recharge. The hydroperiod is thus dependent upon the level of the water table in the nearby surrounding uplands. Water percolates downhill into the basin where it is trapped by stratified organic DODD: ECOLOGY OF SANDHILLS POPULATION OF GAS77?OPHR}NE CAROLINENSIS 15 soil layers beneath the soil surface (LaCIaire and Franz 1990). The pond continuously held water for two years prior to the initiation of my study, but its soil profile suggests that periodic droughts are common (LaCiaire and Smith unpubl.). The pond area was enclosed by a 230-m drift fence made of galvanized metal flashing (36 cm above ground, 10-15 cm below the surface). No vegetation overhung the fence, and the fence and pond area were exposed to direct sunlight. Vegetation was kept cut and away from the fence exposing bare white sand for about 40 cm from the base of the fence in either direction. The distance from the drift fence to the nearest forest cover is generally 20 4 but extends to about 50-60 m behind the Panicum meadow. Within the enclosure, herbaceous hydrophytic vegetation dominated the basin although a few shrubs, including buttonbush (Cephalanthus occidentalis), myrtle holly Ulex myrtifolia), and wax myrtle (A*rica cer(fera), were present. Several sapling longleaf and slash pines (P. emomi) grew within the enclosure. Maidencane and carpetgrass (4xonopus furcatus) comprised 76 percent of the ground cover on vegetation transects (LaClaire and Smith unpubl.). Pitfalls (19-1 black plastic buckets) were placed on opposite sides of the fence at 10-m intervals following the procedures outlined by Gibbons and Semlitsch (1982). In order to minimize the effects of direct sun, the buckets were partially shaded with pegboard slanted over the openings in such a manner that there was plenty of room for transit beneath the boards. Each board was laid flat across the bucket opening on days when the pitfalls were not to be checked in order to prevent desiccation of captured animals. Eastern narrow-mouthed toads were captured even when the boards covered the bucket openings because the seals were not complete. The pitfalls were checked 5 days per week between 0700 h and 0900 h, depending on season, from October 1985 through September 1990 (1,273 days; 83,950 bucket nights). A year was defined as extending from October of one year through September ofthe following year (e.g. "1986" covers October 1985 through September 1986) for purposes of analysis. This yearly partition corresponds better than the calendar year with amphibian activity patterns in north-central Florida. Frogs were measured in the field with a clear plastic ruler (snout-urostyle length [SUL], defined as the tip of snout to the posterior portion of the urostyle) and weighed to the nearest 0.1 g using a Pesola hand-held spring scale. Males have a clearly visible black chin that is present in varying levels of intensity year- round (Anderson 1954). In females the chin is mottled, light, and the same color as the belly (Wright 1932). Females also occasionally contained eggs visible through the ventral body wall. The sex was classified as "unknown" if there was any question about the sex of the animal. Animals smaller than 21 mm SUL generally were considered juveniles (Wright 1932; Anderson, 1954), although the sex of some individuals was difficult to determine at 22-24 mm SUL (also see Hecht and Matalas 1946). Anderson (1954) noted that G. carohnensis show adult secondary sex characteristics across a range of sizes and that determining gonadal 16 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) activity solely from external characters is impossible. I marked frogs by clipping toes using a year-specific cohort sequence; no more than one toe was clipped per foot. I carefully examined all captured animals for regenerated toes. Frogs were released on the opposite side of the fence from where they were captured. In addition to biological data, I recorded maximum and minimum air and water temperature and rainfall since the pitfalls were last checked, current weather conditions, and the occurrence of cyclic weather patterns (e. g. cold fronts, severe storms, etc.). Eastern narrow-mouthed toads marked in one year and recaptured in another year presented special data analysis problems, because I could not determine whether an individual had been caught more than once during the second year. Either combining or excluding counts of previously marked frogs with first-caught frogs will give an imprecise picture of population structure and sex ratio of the breeding population. In the results and discussion below, I arbitrarily chose to exclude multi-year recaptures; descriptive statistics relate to previously unmarked animals caught within a year cohort. Multi-year recaptures are treated separately in the paper. RESULTS Hydroperiod and Rainfall From 1985 to 1990, generally small amounts of rain falling in the vicinity of Breezeway Pond resulted in short hydroperiods at various times of the year (Dodd 1992). Large lakes also dried as the water table dropped > 2.5 m throughout north-central and northeastern Florida from 1988 to 1990. Although the maximum recorded water depth at Breezeway Pond was 75 cm, the pond held water for only 14 mo from January 1985 through September 1990 (Fig. 1). The water table was located 60 cm below the ground surface of the bottom of the pond in October 1989 (LaClaire and Smith unpubl.). By February 1991, the water table had dropped to 2.5 m below the ground surface and the central pond area was colonized by a thick growth of Panicum. The driest months at Breezeway Pond were April and October, whereas the wettest months generally were in the summer, except in 1987 and 1988 (Fig. 1). Less than 300 mm of rain fell in any one month except in September 1988, when a tropical depression brought 270 mm of rain in four days. Rainfall was sporadic, however, and very dry months occurred at all times of the year, especially from October 1988 through September 1990. In the summer (mid-May through mid-September), thunderstorms provided most of the rainfall in the vicinity of Breezeway Pond. However, rainfall from thunderstorms was localized and, during the latter years of the study, was DODD: ECOLOGY OF SANDHILLS POPULATION OF GASTROPHRYNECAROLINENSIS 17 500 m"M IM Mi E ex 400 R A IN FA LL ( m m ) R A IN FA LL ( m m ) 300 ex 200 e e X100 Xe e X 0 111 lili lili OJAJOJAJOJAJ 85 1 86 1 87 1 88 500 %55§ 400 - 300 - e e X 200 100 0 JAJOJAJ 88 1 89 1 90 Fig. 1. Monthly rainfall totals at Breezeway Pond, Putnam Co., Florida, October 1985-September 1990. The stippled bars at the top of the figure illustrate the duration of the hydroperiod. No water was present in the pond at other times of the year. The stars indicate months with substantial movements of Gastrophone carohnensis into (e) or away from (x) the pond- 18 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) insufficient to replenish groundwater depleted by regional drought. North-central Florida experienced a record drought during the latter half of the study based on hydrological data kept by the St. Johns River Water Management District. Other than the 1988 tropical depression, no weather patterns during that period resulted in substantial rainfall at Breezeway Pond. Daily and Seasonal Activity A total of 5740 eastern narrow-mouthed toads, including recaptures, were captured between 1985 and 1990 (Table 1). Most were captured during the first four years of the study, and captures declined dramatically in 1990 as the drought progressed. Eastern narrow-mouthed toads were captured during all months of the year (Table 2), although they were not captured in all months of any one year (Fig. 2). Juveniles were caught more often than adults during the winter months of December through February. Adult males and females entered and exited the pond at all times of the year (Table 2). However, 98% of all adult captures occurred from May through September from 1986 through 1990. During the 1986, 1988, and 1990 field seasons, most activity occurred from June through September (Fig. 2). Juveniles exited the pond basin in the autumn of 1985 and during the spring of 1986, but entered the pond from September through early November 1988. Adult males and females were active not only during the same months of the year (Fig. 2), but also on the same days. A visual examination of capture records from 1986 through 1990 for the months of June, July, and August revealed no temporal differences in the daily capture of males and females. A representative example of the daily capture data for males and females is shown for June 1989 (Fig. 3). Neither sex was active consistently before or after the other sex. Although individuals might be active during very dry periods, rainfall triggered an immediate response. When rain fell from May through September, frogs became active and were encountered at the drift fence. For example, Gastrophgne moved in large numbers on only 10 occasions in June from 1986 through 1990. On eight of these occasions, rainfall totaled 29 mm or greater (Table 3). On the remaining two occasions, the rainfall occurred after long periods without rain. Most eastern narrow-mouthed toads were captured when most of the monthly rainfall was recorded (Table 3). Large numbers of toa(Is moved to Breezeway Pond only in the presence of some rainfall. The presence of standing water within the pond basin had no effect on eastern narrow-mouthed toad movements, i.e. animals went to the pond in mid-summer whether water was present or not (Fig. 1). Frogs entering Breezeway Pond encountered standing water only twice from 1985 through 1990, and in one of DODD: ECOLOGY OF SANDHILLS POPULATION OF GASTROPHRYNECAROUNENSIS 19 Table 1. Captures of unmarked (first number) and marked (second number) Gastrophgne carolinensis at Breezeway Pond Putnam County, Florida 1986-1990. If the sex of an animal could not be determined, it was classified as "Unknown." Year Males Females Juveniles Unknowns Total 1986 193/76 142/48 37' 482/102 854/226 1987 180/164 189/107 1/0 9/3 379/274 1988 507/195 331/130 8/0 31/2 897/327 1989 219/122 181/120 240/35 -- 640/277 1990 55/24 66/36 1/0 1/5 123/65 Total 1154/581 929/441 287/35 523/112 2893/1169 1 An additional 1678 recently metamorphosedjliveniles were not marked in 1986. 1,400 N = 2758 M Unknowns I 3 Juveniles N U M BE R O F IN D IV ID U AL S 1,200 j I Females 1,000 A Males 800 600 N = 1224 ~ N=917 400 a N =653 200 N = 188o L _fl _k_ -&- ODFAJAODFAJAODFAJAODFAJAODFAJA 1985 1986 1987 1988 1989 1990 Fig. 2. Monthly and annual variation in activity patterns ofadult and juvenile Gastrophgne carohnensis at Breezeway Pond, Putnam Co., Florida. Data combined for all captures (N=5740), entering and exiting. 20 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) Table 2. Capture of Gastrophgne carolinensis entering and exiting Breezeway Pond, Putnam County, Florida, by month 1986-1990. The total includes animals for which the sex was not determined. N = 5740. Total Adults Exit Adults Enter Juveniles Month Exit Enter M F M F Enter Exit Jan 1 10 0 0 1 0 9 1 Feb 6 8 2 0 0 1 7 3 Mar 12 25 1 3 4 5 14 7 Apr 0 86 0 0 7 4 72 0 May 195 285 11 10 64 43 164 170 Jun 1130 1018 190 125 364 318 125 737 Jul 507 254 235 138 96 71 7 40 Aug 358 456 192 117 218 187 1 11 Sep 470 230 242 200 83 128 8 3 Oct 361 141 8 8 8 6 115 341 Nov 75 91 6 4 3 2 79 65 Dec 6 13 0 0 0 0 15 6 Total 3121 2619 887 605 848 765 616 1384 100% 80% 1 33*34 - ~99..410 9'.j 40% L. V- - 20% 0% 1 5 7 9 13 15 19 21 23 27 29 DATE E31 Males (197) ~ Females (129) Fig. 3. Proportional capture ofmale and female Gastrphryne carotinensis at Breezeway Pond, Putnam Co., Florida, in June, 1989. Males comprised 60% ofthe sample. Both sexes always were captured on the same day. DODD: ECOLOGY OF SANDHILLS POPULATION OFGASTROPHRYWECAROLINENSIS 21 Table 3. Relationship between the number of adult Gastrophiyne carolinensis captured and daily rainfall during the month ofJune 1986-1990. Rainfall Number % of Monthly Year Date (in mm) Captured Capture Rain 1986 18-22 147 156 75.4 85.5 1987 15-18 2 96 22-26 42 60 68.7 75.9 1988 6-10 29 79 28 2 27 78.5 100 1989 5-14 51 139 20-23 108 89 26-28 67 53 86.1 96.1 1990 7-12 108 45 25-27 136 31 74.5 98.4 those years (1987), the pond dried in June. A cumulative high monthly rainfall total also was not associated with movement to or away from the pond (Fig. 1). The sole exception was associated with a September 1988 tropical depression that drenched north-central Florida. Individual frogs probably went back and forth between the pond basin and upland retreat sites, depending on weather conditions, throughout the breeding season. Most of the eastern narrow-mouthed toads that were captured at the beginning of the activity season in May or June were unmarked (Figs. 4,5) However, the relative proportion of unmarked to marked animals neither remained constant nor decreased, except in 1990. Instead, a second influx of unmarked animals appeared in August and September. The proportion of unmarked to marked animals changed from one year to the next as the activity season progressed, but the within-year patterns were similar between the sexes (Figs. 4, 5). Population Structure The overall sex ratio of unmarked adult (> 23 mm SUL) eastern narrow- mouthed toads was one female for every 1.30 males. A male bias in the sex ratio was present in all years except for 1990 (Table 4). The sex ratio of unmarked animals differed significantly from 1:1 in 1986 (%2=9.95, df=l, p = 22 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) 1986(95%) 1987(98%) 10096 100% ')i'':i; i'Nii i1 7596 - 7596 r., N ./»I' :r5096 - 50% - m 2596 - 25% 096 096JFMAMJJASOND JFMAMJJASOND EEMales U (181) @Males R (74) El Males U (172) ~ Males R (163) 1988 (97%) 1989 (96%) 10096 100% 75% - i«jrf E·!»'ii' t 5096 - 5096 - 25% - 25% - 095;MAMJJASOND 096.1;MAMJJASOND [SMales U (492) &Males R {186) EEMales U (214) 72 Males R (111 ) 1990 (87%) Total 1986-1990 (98%) 10096 111:1'll 100% , , .1 1 75% - 1 11 7596 5096 - 50% - 25% - 25% - 0% 0%JFMAMJJASOND JFMAMJJASOND EEMales U (47) 7&Males R (22) E3Males U (1030) E] Males R (516) Fig, 4. Proportional capture of unmarked (U) to recaptured (R) mate Gastrophryne carolinensis during the priciple activity season at Breezeway Pond, Putnam Co., Florida, 1986 - 1990. The number in parentheses after the year is the percentage of the total number of males captured within that year. 0.0016), 1988 (2=30.57, df=1, p < 0.0001), and in the overall sex ratio from 1986 through 1990 (%2=28.76, df=1, p < 0.0001). In 1990, the ratio was nearly significant (2=3.61, df=l, p = 0.0574). For recaptured animals, the adult sex ratio was one female for every 1.29 males and was male-biased in all years except 1990. DODD: ECOLOGY OF SANDHILLS POPULATION OFGASTROPHRYNECAROUNENSIS 23 1986 (96%) 1987 (98%) 10096 100%'hi"i' .1,1' ';d;''tri'141, 76% - 75% ' ·,1,,11.,'.'.1.'1.1 t,Ij,1.1, 50% - 5096 . 4,4. 25% - 25% 0% JPMAMJJASOND JFMAMJJASOND EI]Females U (139) EZ]Females R (43) EJ Females U (183) ~ Females R (107) 1988 (96%) 1989 (96%) 10096 10096 75% 5096 - 5096 25% 25% 096 , . , , 096JFMAMJJASOND JFMAMJJASOND ~Females U (338) ~Females R (125) EE~ Females U (175) ~ Ferneles R (112) 1990 (97%) Total 1986-1990 (98%) 100% 100% 7596 - 75% - so]96 - * SO96 - 25% - 25% - 0% ·'' 096 JFMAMJJASOND JFMAMJJASOND E®Females U (63} ~Females R (35} E~ Females U (831) 7Females R (411) Fig. 5. Proportional capture of unmarked (U) to recaptured (R) female Gastrophgne carolinensis during the principle activity season at Breezeway Pond, Puham Co., Florida, 1986 - 1990. The number in parentheses after the year is lhe percentage ofthe total number of females captured within that year. There was no trend toward a 1:1 sex ratio as the season progressed in any year (Table 4), Population size structure varied somewhat among years (Fig. 6). In 1987, 1988, and 1990, the population structure was unimodal with few or no juveniles and very large animals among the unmarked toads. In 1986 and 1988, the 24 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) Table 4. Summary of sex ratio data within and among yean for all Gastrophryne carotinens„ captured at Breezeway Pond, Putnam County, Florida during the months of June, July, and August. The tabulation includes all adults captured within that month June July August Year M F Ratio M F Ratio M F Ratio 1986 117 90 1.3:1 94 55 1.7.1 44 37 1.2:1 1987 110 117 0.9.1 91 35 2.6:1 88 82 1.1:1 1988 85 50 1.7:1 84 63 1.3:1 247 133 1.9:1 1989 197 129 1.5.1 41 27 1.5:1 27 40 0.7:1 1990 45 57 0.8:1 21 29 0.7:1 4 12 0.3:1 Table 5. Analysis of variance of differences in snout-urostyle length (SUL) and weight among years between the sexes of unmarked adult Gastrophone carolinensis, 1986-1990. No weight data were available for 1987. Values are for Type I[I sums of squares. Variable Year Sex Year*Sex SUL F=115.24 F=186.53 F=16.56 p=0.0001 P=0.0001 p=0.0001 4 df 1 df 4 df Weight F=46.85 F=329.52 F =1.43 p=0.0001 p=0.0001 p=0.2316 3 df 1 df 3 df population structure was bimodal with the appearance of recently metamorphosed young from the 1985 breeding season (exiting Breezeway Pond in 1986) and from immigrants from some other location in 1988 (entering Breezeway Pond in September, October, and November). Despite the lack of reproduction at Breezeway Pond from 1986 through 1990, the population structure did not shift appreciably toward large adults as the study progressed. In 1990, a small number of eastern narrow-mouthed toads came to the pond, but the adult size structure did not differ from previous years. DODD: ECOLOGY OF SANDHILLS POPULATION OF GASTROPHR}WECAROUNENSIS 25 Table 6. Descriptive statistics for snout-urostyle length showing number, range, mean, and standard deviation (in mm) of unmarked Gastrophryne carolinensis caught at Breezeway Pond, Putnam County, Florida 1986-1990. Year Males Females Juveniles Unknowns 1986 N 137 89 36 326 Range (22-33) (23-35) (14-19) (20-33) Mean 27.8 28.8 18.1 22.8 S.D. 1.52 2.36 1.18 1.78 1987 N 180 189 5 Range (22-34) (21-34) (21-26) Mean 26.4 26.5 22.8 S.D. 1.50 2.60 1.92 1988 N 376 239 8 Range (24-31) (24-34) (11-14) - Mean 27.5 29.1 12.9 S.D. 1.31 0.38 1.13 1989 N 219 181 222 Range (24-32) (24-35) (11-24) - Mean 28.1 30.1 15.9 S.D. 1.43 1.99 2.37 1990 N 55 66 1 1 Range (24-30) (25-33) Mean 27.1 29.0 22 25 S.D. 1.26 1.68 Significant differences in SUL and weights occurred among years and between sexes (Table 5), except for the year*sex interaction in weight. Differences among mean adult SULs and weights were generally small (Tables 6,7). Adult males were shorter and weighed less than adult females in all years, although the difference was slight in 1987. The largest mean SUL for both males and females 26 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) Table 7. Descriptive statistics for weight showing number, range, mean, and standard deviation (in mm) of unmarked Gastrophone carolinensis caught at Breezeway Pond, Putnam County, Florida, 1986-1990. Weights were not recorded in 1987. Year Mates Females Juveniles Unknowns 1986 N 137 89 33 318 Range (1.0-2.9) (0.8-4.8) (0.2-0.7) (0.5-2.5) Mean 1.93 2.29 0.52 1.10 S.D. 0.30 0.66 0.11 0.30 1988 N 301 177 8 - Range (0.6-2.5) (1.2-3.0) (0.1-0.3) - Mean 1.62 2.04 0.19 - S.D. 0.20 0.38 0.06 - 1989 N 206 176 198 --- Range (1.14.8) (0.9-3.2) (0.1-1.0) Mean 1.75 2.23 0.35 - S.D. 0.24 0.44 0.16 - 1990 N 54 66 1 1 Range (1.2-2.7) (1.5-3.4) - - Mean 1.93 2.42 1.1 0.6 S.D. 0.29 0.43 - - was in 1989, whereas the smallest mean SUL for both was in 1987. The largest male was 32 mm SUL, whereas the largest female was 35 mm SUL. Adult females weighed more than adult males in all years. Weights were greatest for adult males in 1986 and 1990, and for females in 1990. Multi-Year Recaptures Most recaptured eastern narrow-mouthed toads were caught within the same year they were marked (Table 1), but 134 multi-year recaptures were DODD: ECOLOGY OF SANDHILLS POPULATION OF GAS7ROPHRYWECAROLINENSIS 27 NU M BE R CA PT UR ED NU M BE R CA PT UR ED 7 ' 100 1986 1987 137M 180 M 80 89F * 189F 36 J 5U 60 326 u ~~ 40 lill Ill' 44 •IM@%435 ._-, ' '4 44<4111.20 ~44*4 /~ *N IN , 14 18 22 26 30 34 21 25 29 33 SUL (mm) SUL (mm) WMales IFemales EJJuveniles EUnknowns B 200 1988 374 M 150 239 F 1989 8J 219 M 1990 181 F100 55 M 222 J 66 F 1 J f lU 50 fmL 11 15 19 2327 31 11 15 19 23 27 31 35 23 2731 SUL (mm) SUL (mm) SUL (mm) E Males ~ Females U Juveniles ~ Unknowns Figure 6. Annual variation in size-class structure of Gastrophome carolinensis at Breezeway Pond Putnam Co., Florida. A 1986 -1987. B. 1988-1990. An additional 1679 juveniles < 15 mm SUL were captured in 1986. Note the difference in scale. recorded (Table 8). Most multi-year recaptures were marked in one year and observed during the following year. Multi-year recaptures included both immigrants to and emigrants from the pond throughout the activity season, and made it impossible to determine how often they were caught within a season. The size-class distribution of toads captured after one year spanned nearly the entire range of size classes captured during the study (Fig. 7). However, the size- class distributions of eastern narrow-mouthed toads captured after two and three 28 BULLETIN FLORIDA MUSEUM NATURAL HISTORY 38(1) 1 20 f Ill Y 10 6E=&= 5 @AN ~Mili