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sity of Central Florida Animal Use and Care Committee (Protocol #0105)and all methods adhered to the guidelines set forth by the InstitutionalAnimal Care and Use Committee for Wildlife Field Studies.

LITERATURE CITED

BISHOP, L. A., T. M. FARRELL, AND P. G. MAY. 1996. Sexual dimorphism ina Florida population of the rattlesnake, Sistrurus miliarius.Herpetologica 52:360364.

COOK, P. M., M. P. ROWE, AND R. W. VAN DEVENDER. 1994. Allometric

scaling and interspecific differences in the rattling sounds of rattle-snakes. Herpetologica50:358368.DUVALL, D., M. B. KING, AND K. J. GUTZWILLER. 1985. Behavioral ecology

and ethology of the prairie rattlesnake. Nat. Geogr. Res. 1:80111.GREENE, H. W. 1973. Defensive tail display by snakes and amphisbaenians.

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Huey (eds.), Biology of the Reptilia. Vol.16, pp. 1152.Alan R. Liss,New York.

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KLAUBER, L. M. 1972. Rattlesnakes: Their Habits, Life Histories, and In-fluence on Mankind. 2nd edition. University of California Press, Ber-keley, California.

NEILL, W. T. 1960. The caudal lure of various juvenile snakes. Quart. J.Florida Acad. Sci. 23:173200.

RABATSKY, A. M. 2002. Caudal luring and defensive tail display in thedusky pigmy rattlesnake, Sistrurus miliarius barbouri. M.S. Thesis,University of Central Florida, Orlando. 34 pp.

, AND J. M. WATERMAN. 2005. Ontogenetic shifts and sex differ-ences in caudal luring in the dusky pygmy rattlesnake, Sistrurusmiliarius barbouri. Herpetologica 61:8791.

ROWE, M. P., T. M. FARRELL, AND P. G. MAY. 2002. Rattle loss in pygmyrattlesnakes (Sistrurus miliarius): Causes, consequences, and implica-tions for rattle function and evolution.In G. W. Schuett, M. Hoggren,M. E. Douglas, and H. W. Greene (eds.), Biology of the Vipers, pp.

385404. Eagle Mountain Publishing, Utah.

Herpetological Review, 2005, 36(3), 238241. 2005 by Society for the Study of Amphibians and Reptiles

Diet Composition and Microhabitat ofEleutherodactylusjohnstonei in an Introduced

Population at Bucaramanga City, Colombia

JESS EDUARDO ORTEGAColeccin Herpetolgica, Grupo de Estudios en Biodiversidad

Escuela de Biologa, Universidad Industrial de SantanderBucaramanga, Colombia

e-mail: ortegachinchilla@yahoo.com.mx

VCTOR HUGO SERRANOLaboratorio de Biologa Reproductiva de Vertebrados

Grupo de Estudios en Biodiversidad, Escuela de Biologa

Universidad Industrial de Santander, Bucaramanga, Colombia

e-mail: vserrano@uis.edu.co

and

MARTHA PATRICIA RAMREZ PINILLAColeccin Herpetolgica and

Laboratorio de Biologa Reproductiva de Vertebrados

Grupo de Estudios en Biodiversidad, Escuela de Biologa

Universidad Industrial de Santander, Bucaramanga, Colombia

e-mail: mpramir@uis.edu.co

Eleutherodactylusjohnstonei Barbour 1914 is an endemic spe-cies of many islands of the Lesser Antilles (Frost1985). It is widelydistributed in the Eastern Caribbean (Kaiser and Hardy 1994) andin northern South America (Frost 1985; Kaiser et al. 2002; Ovaska1991) where it is associated with urban areas. It has been intro-duced by natural phenomena and by human activity (Kaiser et al.2002). In Colombia it has been reported in the cities of Barranquilla(Acosta - Galvis 2000; Ruiz-C. et al. 1996), Cali (F. Castro inKaiser et al.2002), and Bucaramanga (Ortega et al. 2002).

Diet and microhabitat use ofE. johnstonei have been studiedonly ina population of Barbados (Ovaska 1991), where the spe-

cies is probably indigenous (Marsh 1983). For this population themost abundant prey found was Formicidae, followed by collem-bolans, dipterans, and homopterans, among others. The individu-als of this population use bromeliads, trunks, leaf litter, and smallrocks as diurnal refuges, and during the night they are active acrossthe arboreal stratum. In recently colonized areas, these ecologicaldata have not been recorded although such information could con-tribute to an understanding of why this species is a successful in-vader. Here, we report on diet composition and microhabitat usein an introduced population ofEleutherodactylus johnstonei andcompare these data with those from native populations.

Materials and Methods.The studied population is located inthe house gardens of Bucaramanga (Santander, Colombia; 0707'

28.7"N and 7306'41.6"W, 1040 m altitude). The area has a nearlyconstant bimodal regime of rains and a mean temperature of 24Cduring the year. The vegetation in the gardens is characterized bya variety of ornamental plants. Individual frogs were collected ingardens in leaf litter and on bushes between 2000 and 2200 h.Additional searches were made in forests bordering the study site,to determine presence adjacent to gardens and whether there hasbeen displacement of native frogs by the introduction ofE.johnstonei. Initially, we collected 30 frogs and made an analysisof minimum sample size using a saturation curve of consumedprey. We monthly collect 1720 individuals each month (May of

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Herpetological Review 36(3), 2005 239

2001 through April of 2002) following the suggestions of this pre-vious analysis. We collected frogs larger than 15 mm snoutventlength (SVL) to facilitate handling in the laboratory. Followingthe suggestions of Heyer et al. (1994), we recorded SVL, mouthwidth (MW), substrate type (soil, leaf litter, leaves, trunks, rocks,and grass) and perch height. Individuals were euthanized and fixedin 10% formalin to interrupt the digestive processes and prey de-composition. Specimens were deposited in the Herpetological Col-lection of the Museo de Historia Natural, Universidad Industrial

de Santander (UIS-A).Leaf litter arthropods were collected with an insect net andBerlesse funnel at the study location. They were preserved in 70%ethanol and were used as reference samples for comparisons anddetermination of the stomach contents of the collected frogs. Di-gestive tracts of each individual were removed and their contentspreserved in 70% ethanol. Taxonomic determinations of prey weremade using the keys of Borror et al. (1989). Fragments that showedidentification problems were compared with preserved samplesof arthropods. Number and percentage of prey per stomach wasrecorded. An index of relative importance was calculated to evalu-ate the contribution of each category to this populations diet (fol-lowing Pinkas et al. 1971). We tested correlations between frog

SVL and MW and the size and volume (using the ovoid spheroidformula, Caldwell and Vitt 1999) of the ingested prey to see iprey size depends on frog corporal size or mouth size. Chi-squartests were used to investigate whether significant statistical differences existed in the use of the microhabitat and perch height.

Results and Discussion.We dissected 212 stomachs (140 maleand 72 females), revealing 1448 prey items identified to orderand grouped into 22 categories excepting members of FormicidaeDiet was composed of insects and other arthropods such as spi

ders and isopods (Crustacea), and other prey as gastropods andoligochaetes (Table 1). Although there was some plant material inthe diet, these were not included because only two of the 212 dissected stomachs contained these items.

Traditionally it has been thought that anurans have a generalisdiet, which reflects the richness and size of the resource (Duellmanand Trueb 1986). Our results suggest thatE. johnstonei is a carnivorous generalist species as determined by the presence of avariety of prey items such as homopterans, orthopteransthysanopterans, dermapterans, gastropods, formicids, collembolans, and isopods. A generalist diet is likely one of the characteristics (but not the only one) that makes this frog an excellent colonizer.

TABLE 1. Diet composition of males and females of an introduced population ofEleutherodactylus johnstonei . Numerical importance(number of prey item in relation to total number of items found in the species), frequency (percentage of prey item number in relation tototal number of items found in the species), prey volume (total volume of prey category in all individuals examined), and percentage ofrelative importance [IRI = % FO (%V + %N), FO, percentage of stomachs containing an specific item, V volumetric importance, and N,numerical importance].

Numerical Importance Frequency Prey volume % IRI

Prey Males Females Males Females Males Females Males Females

Formicidae 435 260 96 64 248.31 169.13 5780.6 4309.1

Diptera 120 135 58 45 82.73 108.48 1026.9 1657.

Collembola 84 35 24 14 5.34 6.34 200.3 106

Homoptera 16 18 14 14 76.87 41.15 84.7 103

Hymenoptera 13 10 9 9 82.9 12.34 68.3 28.1

Heteroptera 2 7 1 7 2.61 93.54 0.4 69.4

Orthoptera 1 2 1 2 0 3.19 0.1 1.4

Dermaptera 6 3 6 2 16.17 5 10.9 2.1

Nymphs 8 4 5 3 11.57 11.2 8.2 5.4

Caterpillar 22 17 8 7 62.75 462.43 55.2 318.6

Gasteropoda-1 10 9 9 6 48.91 83.44 42.3 56.3

Scolopendra 2 2 2 2 1.6 0 0.6 0.8

Larvas 8 7 7 6 15.7 26.35 13.7 22.8

Coleoptera 13 20 10 14 122.97 69.6 106.8 144.5

Gasteropoda-2 0 1 0 1 0 48.7 0 4.6Acari 20 11 14 9 1.75 1.05 28.3 20.6

Blattaria 9 3 5 3 115.48 38.26 48.6 1.2

Isopoda 23 15 11 10 85.69 59.37 96.3 84

Thysanoptera 13 0 2 0 4.34 0 3.1 0

Pseudoscorpion 2 0 2 0 1.46 0 2.6 0

Oligoquete 2 0 2 0 14.03 0 2.5 0

Araneae 11 10 11 9 6.26 6.54 25.2 23.3

TOTAL 820 569 129 88 1007.4 1246.12 7605.6 6958.7

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240 Herpetological Review 36(3), 2005

The 22 taxonomic prey categories contribute to the individualsdevelopment according to the index of relative importance (IRI).The most important category was Formicidae (54.24%) followedby dipterans (47.16%) and collembolans (19.33%), whereas thecategories with a low IRI possibly reflect opportunistic ingestionsrelated to the abundance of these resources in the study place. InotherE. johnstonei populations, ants were the most important prey(51.4% in Barbados; Ovaska 1991), and in Jamaica, Stewart (1979)reported two introduced species (E.johnstoneiandE.planirostris)

and two native species (E. gossei and E. cundalli) whose mainfood source was Formicidae. Also, inE. coqui,Lavigne and Drewry(1971) found that ants were the most consumed prey, and Duellman(1978) found that for 9 of 15 species ofEleutherodactylus, antswere the most consumed prey. The high percentage of ants in thediet might suggest a high availability of this resource in the sam-pling places not measured by any of these investigators (nor us),or that these species specialize upon ants.

However, other species ofEleutherodactylusare not consumersof ants. Arroyo (2002) reported collembolans and coleopterans asthe most important prey for anEleutherodactylusassemblage in acloud forest of the Cordillera Oriental of the Colombian Andes.Gutierrez (2003) reported, for another assemblage of cloud forest

Eleutherodactylus, that the most common prey items were iso-pods and coleopterans, in an area south of the location studied byArroyo (2002). Ants were items that frogs consumed only occa-sionally in both studies; in fact, ants are typically rare at higherelevations including cloud forests. Thus, prey availability mightexplain the differences in diet amongEleutherodactylus species.Duellman and Trueb (1986) suggest external factors (seasonalabundance of the food and competitors presence or absence) andintrinsic factors (ecological and morphological tolerances) relat-ing to body size with the election and type of prey consumed, andwith use of microhabitats for foraging.

Prey composition of each sex was not significantly different(Z(139,71) = -0.776212; P = 0.4376). There was also no significant

differences among sexes in the numeric importance (U(1,21) =209.500; P = 0.445), frequency in the stomachs (U(1,21) = 221; P =0.622), volume of the ingested prey (U(1,21) = 236; P = 0.88) andthe relative importance index (U(1,21) = 226.5; P = 0.91, Table 1).

The adult population ofE.johnstonei showed a positive rela-tionship between SVL and MW and the size and volume of theconsumed prey. There was a significant correlation between SVLand prey size (r= 0.1983; P = 0.0036; N = 212) and prey volume(r= 0.148; P = 0.0308; N = 212). Similarly, there was a significantcorrelation between MW and prey size (r= 0.1689; P = 0.0135; N= 212) and MW and prey volume (r= 0.1974; P = 0.0038; N =212) indicating that larger frogs and bigger mouths ingest largerprey. These relationships were also reported in a native popula-tion ofE. johnstonei in Barbados (Ovaska 1991), in E. coqui(Woolbright and Stewart1987), in six sympatric species of anuransthe central Amazonian (Lima 1998), and in a subtropical commu-nity of anurans (Basso 1990) showing that changes in size andprey types with the sizes of frogs are expected by morphologicalreasons and for changes in the spectrum of types of prey that canbe ingested (Lima and Magnusson 2000).The positive relation-ship between MW and the size and volume of the prey constitutesan important element sustaining is ideas Toft (1980, 1981) that thewidth of the mouth limits the size of the prey captured by certain

species.Eleutherodactylusjohnstonei used vegetation associated with

the herbaceous substrate (families Araceae, Bromeliaceae,Conmelinaceae, and Poaceae) as places for calling and perching.Trees taller than 2 m (families Combretaceae and Rutaceae)provided protection against solar radiation/drying and maintainedsoil moisture. The analysis of substrate use allowed us to establishsignificant differences for this resource (soil, leaf litter, leaves,trunks, rocks, and grass) intersexually (2(0,05;5) = 13.11; P > 0.01)

and intrasexually (males, 2

(0,05;5) = 48.3; P < 0.001 and females2(0,05;5) = 32.86; P < 0.001, Fig. 1).Perch height used is also different between the sexes (2(0,05; 6) =

16.79; P < 0.01); males perch higher than females to call, andfemales prefer lower perches. Among males there were no signifi-cant differences in perch height (2(0,05;6) = 9.3; P > 0.10), contraryto from females who showed significantly different perch heights(2(0,05;5) = 32.74; P < 0.001) (Fig. 2).

Most of the males were collected calling on the bush substratewhereas females were collected close to the calling sites at lowerperch heights. These intersexual differences are presumed to berelated with reproductive behaviors: males use higher perches tocall before amplexus, but when oviposition occurs they descend

to the ground because males care for the eggs, changing their useof the vertical position. Females are more associated with the soiland leaf litter, presumably in relationship with their reproductivebehavior and maybe to avoid capture by predators or disturbance.Similar results were obtained inE.fitzingeri (Hbel 1999) and inanurans of Anchicay where the males are arboreal and the fe-males are associated with the soil and leaf litter (Vargas and Castro1999).Thus, the substrate and perch height used for by frogs maybe more closely related to reproduction than with food availabil-ity, although these two activities are not completely separated.

At Bucaramanga,E.johnstonei is limited exclusively to the veg-etation of the gardens. In the forest patches near to the gardens,we did not findE.johnstonei nor did we hear their song. In this

FIG. 1. Substrate used by Eleutherodactylus johnstonei (inter andintrasexes). 1) soil, 2) leaf litter, 3) leaves, 4) trunks, 5) rocks, 6) grass.Analysis of substrate use showed that there were significant differencesfor this resource intersexually and intrasexually.

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FIG. 2. Perch height used by both sexes ofEleutherodactylus johnstonei.Males, white blocks; females, black blocks. Intersexual differences inperch height ranges are presumed to be associated with reproductive be-haviors: most males were found calling on leaves of bushes whereas egg-guarding males and females were found at lower perches in different sub-strates.

zone, we found native species (E. raniformis and E. taeniatus),

which are absent from the gardens of the city. The adjacent veg-etation of the neighborhood where the population ofE.johnstoneiis found corresponds to a highly disturbed tropical dry forest onthe Andean slopes to the east of the city. Possibly this forest doesnot have the humidity and microhabitat features required for thesurvival of the species, similar to those permanently irrigated gar-dens, which can provide an ideal habitat for reproduction and otherphysiological aspects. Because native species are absent in theresidential areas,E.johnstonei enjoys great success in these emptyniches. Thus, at present, we have not been able to observe dis-placement of native species by the arrival ofE. johnstonei. Al-thoughE.johnstonei is a generalist species in diet and microhabi-tat use allowing it to easily colonize new territories, these charac-

teristics do not explain why this species is associated almost ex-clusively with houses gardens and not other neighboring disturbedareas at this locality.

Acknowledgments.We thank the Laboratorio de BiologaReproductiva de Vertebrados of the Universidad Industrial de Santanderfor economical support to this project, the use chemicals and laboratoryequipment, the Corporacin Regional para la Defensa de la Meseta deBucaramanga (CDMB) for the collection permits, and L. Navarro, G.Castillo and M. Baron, students of the Escuela de Biologa, UIS, for helpin the capture of the frogs. We also thank John D. Lynch for his importantcomments on the manuscript and for his help reviewing the English.

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