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Structure of Transient Vocal Assemblages of Physalaemus fischeri (Anura,Leiuperidae): Calling Site Fidelity and Spatial Distribution of MalesAuthor(s): Zaida TáranoSource: South American Journal of Herpetology, 4(1):43-50. 2009.Published By: Brazilian Society of HerpetologyDOI: http://dx.doi.org/10.2994/057.004.0105URL: http://www.bioone.org/doi/full/10.2994/057.004.0105

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STRUCTURE OF TRANSIENT VOCAL ASSEMBLAGES OF PHYSALAEMUS FISCHERI (ANURA, LEIUPERIDAE): CALLING SITE

FIDELITY AND SPATIAL DISTRIBUTION OF MALES

ZAIDA TÁRANO*

* Universidad Central de Venezuela, Instituto de Biología Experimental, Apartado 47106, Caracas 1041A, Venezuela. E-mails: zaida.tarano@ciens.ucv.ve, ztarano@yahoo.com

ABSTRACT. Breeding aggregations are common in anurans during reproduction. In these aggregations, males can space themselves or randomly distribute themselves in the available space, and they can occupy the same position for long periods of time or shift from one position to another frequently. I investigated male spacing patterns and individual site fidelity of Physalaemus fischeri at a moderately flooded shrub plot during 21 consecutive nights at a locality in the central llanos of Venezuela. Male positions and nearest neighbor distances were determined nightly. I found 35 different males at 53 calling positions. Not all males were active simultaneously. Nineteen males occupied the same calling position for more than one night, either consecutively or not. The number of nights of consecutive occupation of a position by the same male was 2.59 ± 1.12 (mean ± sd; max = 5 nights, N = 17 males) and the total number of nights (consecutive and non-consecutive) was 3.00 ± 1.41 (mean ± sd; max = 6 nights, N = 15 males). Themodal nearest neighbor distance was 2.5 m and about 58% of the inter-male distances were below 6 m. The Clark and Evans index (R) and the Thompson’s test, performed for each observation night, indicated that males distributed themselves regularly in most nights. There was a positive association between R and nearest neighbor distances (Spearman rs = 0.72, p = 0.04), thus, regular spacing was associated with spatial segregation among males. The results indicate that breeding aggregations of P. fischeri males are structured but dynamic, because males space themselves within the aggregation and show site fidelity, but only during a few nights. Male segregation is suggestive of acoustically mediated spacing, because male-male combat was rare. In addition, spacing and occupation of a stable position over short periods may entail breeding advantages that still remain to be investigated.

KEYWORDS. Physalaemus fischeri, nearest neighbor distance, anuran, chorus, prolonged breeder, spacing, territoriality.

Spacing among calling males in breeding choruses has important consequences for conspecific commu-nication and mating, especially for female attraction. Spacing determines the degree of overlap in male acoustic ranges and also the probability of direct in-terference during courtship (Wells, 1977; Ovaska and Hunte, 1992). Acoustic interference can impair male localization and choice by females (e.g. Schwartz, 1993; Tárano and Herrera, 2003). In spite of this det-rimental effect, acoustic ranges of males in breeding aggregations are likely to overlap when inter-male distances are much shorter than the transmission dis-tance of the call or than the male’s active space (i.e., space around the male where the signal is detectable and may elicit a response in the receiver). Thus, in chorusing species, male aggregation on a larger spa-tial scale is often opposed by separation on a shorter scale. In a number of anurans, inter-male spacing is achieved through physical interactions (e.g., Arak,1983), acoustic interactions (e.g., Robertson, 1984) or a combination of both (e.g., Telford, 1985; Ovas-ka and Hunte, 1992; Beiver et al., 2006). Therefore,chorus organization is frequently assumed to be a consequence of male-male competition. In most an-urans, only one call, the advertisement call, mediates male interactions and female attraction (Wells, 1977).

INTRODUCTION

Individuals in natural populations usually have complex spatial distributions that can also vary in time. For example, individuals can aggregate at some spatial scale and move away from each other at an-other; therefore, detecting particular patterns within a population can be difficult. When detected, spacing patterns might also be difficult to interpret. Spacing may result from the availability of suitable habitats or microhabitats, mating system, aggressive behav-iors, mate attraction, a combination of neighbor in-trusion and mate attraction or advantages in predator avoidance (reviews in Bradbury and Gibson, 1983; Gerhardt and Huber, 2002). The formation of breed-ing aggregations among explosive and prolonged anuran breeders is well documented (Arak, 1983). In prolonged breeders, males usually form stable, long-term aggregations (choruses) in which they advertise their presence with species-specific vocal-izations. Frequently, males maintain individual dis-tances (Wells, 1977; Gerhardt et al., 1989), often re-sulting in non-random spacing (e.g., Wilczynski and Brenowitz, 1988; Bourne, 1992; but see Ovaska and Hunte, 1992, for random spacing in Eleutherodacty-lus johnstonei).

South American Journal of Herpetology, 4(1), 2009, 43-50© 2009 Brazilian Society of Herpetology

In several species, the amplitude of the advertisement calls of the immediate neighbors is the proximate cue that regulates inter-male distances (Gerhardt and Hu-ber, 2002).

Site tenacity or fidelity, the return and reuse of a position previously occupied over several nights within or between reproductive seasons, occurs in many prolonged breeders (e.g., Whitney and Krebs, 1975; Carpenter and Guillingham, 1987; Given,1988; Bourne, 1992; Caldwell and Shepard, 2007). Defense of resource-based territories and of nightly calling positions are the most common reproductive strategies in prolonged breeders (Wells, 1977; Arak,1983). In most territorial species, males occupy the same calling position within the territory throughout the reproductive season or shift between a few sites within the territory (Given, 1988; Bee, 2002). Site at-tachment has also been observed in species that do not defend resources, but instead occupy calling posi-tions that can be aggressively defended or not. Forinstance, males of Scinax ruber defend small adver-tisement territories to which they return after spawn-ing elsewhere, and males of Rhinella ocellata remain within a small, non-defended area for several weeks (Caldwell and Shepard, 2007). The occupation and defense of nightly calling positions can be advanta-geous if it helps to maintain exclusive advertising areas and reduce acoustic or direct interference with competitors, as observed in Hyla versicolor (Fell-ers, 1979) and Pseudacris crucifer (Marshall et al.,2003). Despite the potential advantages of site fidel-ity in prolonged breeders, males of many species move frequently from position to position within and between nights (Arak, 1983; Bevier et al., 2006). Thehabitat structure, age and the cost of mobility can also influence site fidelity in territorial and non-territorial species. According to Switzer’s (1993) model, in pre-dictable habitats, site fidelity should be inversely re-lated to territory heterogeneity, and positively related to the cost of changing territories, age and previous reproductive outcome at a site. On the contrary, in unpredictable habitats, site fidelity should not relate to previous reproductive success, but to the homoge-neity of territories.

Physalaemus fischeri (Boulenger, 1890) (= P. en-esefae, synonymy by Gorzula and Señaris, 1998) is a prolonged breeder that occurs in the lowlands of northern South America (elevation < 300 m), spe-cifically in the flooded savannas (llanos) of Colombiaand Venezuela (Frost, 2008). In Venezuela, P. fisch-eri is found during the rainy season, when it breeds from June to mid September (Tárano, 2001; Tárano

and Herrera, 2003). Despite its abundance, P. fischeriis a relatively poorly known species. Males call while floating on shallow stagnant water and vocal activity begins at dusk and may last until 04:00h, depending on daily rainfall. Calling sites are located in the shal-lowest parts of the flooded area (< 10 cm) and do not contain valuable resources for females; females ap-proach calling males and then move to another site for oviposition (pers. obs.). Habitat and microhabitat occupation depends on rainfall regime (pers. obs.). Shallow water dries out after a few days without rain and males often move from site to site, within a flood-ed area or between these areas, in search of humid sites. However, if rain is intense and flooding exceeds certain limits, males may abandon a chorus and move to less flooded areas (pers. obs.). Male movements between flooded areas may involve travel distances of at least 500 m in consecutive nights (pers. obs.). Therefore, habitats occupied at the onset of the rainy season might not be occupied later. With such high potential of daily changes in habitat and microhabitat conditions, I asked whether or not the distribution of males was random and whether calling site fidelity occurred. Field observations indicated that calling males were tolerant to nearby active and silent males (Tárano and Herrera, 2003) and that male-male com-bat was rare (Tárano, 2007), thus active male spacing might not occur in this species. In addition, observa-tions during early field seasons suggested that males tended to occupy the same calling positions within and between nights. When mechanically disturbed, males hide but often return to the same calling posi-tion after several minutes (pers. obs.). In this study, I investigated male spacing patterns and individual site fidelity during several consecutive nights at a breeding aggregation in a locality in the central llanos of Venezuela. I tested the hypothesis that males of P. fischeri show prolonged site attachment and that male spacing is random.

MATERIALS AND METHODS

Study Site

Observations were performed at Fundo PecuarioMasaguaral (8°34’N, 67°35’O), a cattle ranch with a large protected area, in Guárico State, Central Llanosof Venezuela. This ranch occupies a nearly flat (el-evation variation < 10 m) open grassland, interrupted by gallery forests that floods during the rainy season. Four physiographic savanna units are found: fossil

Vocal assemblages of Physalaemus fischeri44

sand hill, non-flooded low ridge, moderately flood-ed lowlands (bajíos) and deeply flooded plot (Troth,1979). Physalaemus fischeri males are intensely dis-tributed in the study site but preferentially occupy moderately flooded lowlands with water levels be-low 10 cm. I observed male activity at a moderately flooded shrub plot (shrub-bajío in Troth, 1979) with emergent vegetation dominated by grasses, sedges and scattered shrubs. At the height of the rainy sea-son, water depth varied from 10 to 30 cm and call-ing males were always found in the shallowest areas of the bajío. The sampled area varied in water level and male distribution from one night to another. Themaximum area sampled per night was 752 m2 and the minimum was 205 m2, depending on flooding level.

Male Activity

I registered male activity during 21 successive nights, from June 6 to 26, 2007. I visited the bajío nightly from 21:00 h onwards in search of calling males. All calling males were located with the aid of a 6-V headlamp. Males did not abandon their calling positions when the light focused on them momen-tarily, although they could cease calling. They only abandoned their calling positions when closely ap-proached and if so, typically returned within a few minutes. Calling positions were marked with a num-bered flag that contained male identity and date of observation. The nearest neighbor distances were measured in the morning. During successive surveys, I checked for the presence of calling males at marked positions and registered position shifts between nights to estimate male site fidelity. I also registered the presence of new (unmarked) males. I performed these observations as part of a long-term study on male vo-cal behavior, thus many males had been previously toe-clipped or leg banded (with temporary home-made tiny plastic bands around their thighs) to allow individual identification. Successive observations of toe-clipped males at calling sites and recordings of amplexus and nest construction suggested that this procedure was not detrimental, at least on the short-term. Rainfall was registered daily to investigate its effect on male activity.

Male Spacing Patterns

Nearest neighbor distances for all active males at the site were measured nightly from June 13 to

26, 2007. Male spacing patterns were quantitatively analyzed through the Clark and Evans index (1954) and the Thompson’s test (1956). Clark and Evans proposed an aggregation index, R that represents the ratio of the observed (rA) to the expected (rE) mean

of nearest neighbor distances in an area ( ).For random distributions, the expected mean dis-

tance has a value of , where m represents population density. R varies from 0 to 2.1491, with values indicative of perfectly uniform, random, and completely aggregated distributions. R = 1 corre-sponds to random distribution; R = 0, corresponds to maximal aggregation since, theoretically, all in-dividuals occupy the same location and the nearest neighbor distance is 0. Under maximum regular spacing, R = 2.1491, individuals distribute in a hex-agonal fashion, and each male is equally distant to the other six males. In a given distribution, the mean nearest distance of neighbors is R times as great as that expected in a random distribution. Thus, an Rvalue of 0.5 would indicate that the nearest neigh-bors are, on average, half as far as expected under a random distribution. Significance of R can be tested by calculating the standard variate of the normal

distribution , where E is the standard er-ror of the mean distance to the nearest neighbor in a randomly distributed population of the same density as that of the study population (Clark and Evans,

1954). Therefore , where N is the num-ber of individuals. The c value 1.96 represents the 5% level of significance for a two-tailed test.

The Thompson’s test (1956) was applied to the first and to the second nearest neighbor. The test

is given by with d.f. = 2 Nk, where is the population density, ri is the distance to the kth neighbor, k is the rank of neighbors being mea-sured (k = 1 nearest neighbor; k = 2 second neigh-bor) and N is the number of individuals measured. The significance of this value is obtained by com-

2 distribution 2 2

0.9752 is greater

20.025 spacing is regular. When d.f > 30 the

normal distribution is used: .

Tárano, Z. 45

RESULTS

Site Fidelity

I located 53 calling positions, used by 35 differ-ent males, throughout the observation period. Not all 35 males were active simultaneously. The maximum number of simultaneously active males found in a single night was 16 (16 June). The number of active males varied considerably between nights (Table 1)and was negatively associated with the number of previous days without rain (Spearman: rs = -0.64,p = 0.013, N = 14). Nineteen males occupied the same calling position for more than one night, either consecutively or not. The number of consecutive nights that a male was observed at the same calling position was 2.59 ± 1.12 (mean ± sd; max = 5 nights, N = 17) and the total number of days (consecutive and non-consecutive) of occupancy of a position was 3 ± 1.41 (mean ± sd; max = 6 nights, N = 15). Only a few males changed their calling position on consecu-tive nights due to the dryness of their previous posi-tion, and these shifts were always inferior to 2.5 m(1.92 ± 0.53 m, N = 7), whereas other males left the chorus when their sites dried out. Hence, the number of consecutive nights that a male was active depend-ed on the water level at the calling position. Majorchanges in male activity were associated with flood-ing and occurred after rainfall above 30 mm, on June 16, 22, 25 and 26.

Male Spacing

Qualitatively, males did not distribute themselves throughout the observation plot (Fig. 1), despite the fact that small puddles were available all over the

area at the beginning of the observation period. Malestended to occupy (“preferred”) particular patches in the plot (Fig. 1) and avoided the lower areas (the central portion of the plot) that held more water (wa-ter depth around or above 10 cm). At the end of the observation period (26-June), and after two days of heavy rain (30 and 40 mm respectively), males gath-ered at the southeastern portion of the plot. The north-ern area, previously used by males, as well as the western margin, were deeply flooded. Quantitatively, during 13 consecutive nights, the nearest neighbor distances varied from 0.70 to 55.20 m (mean ± sd:6.94 ± 8.94 m). The modal nearest neighbor distance was 2.5 m and about 58% of the inter-male distances

FIGURE 1. Male distribution on four nights of high activity at the study plot. The doted line represents the plot boundary when flooding is maximal. Water level increases toward the center of the plot.

TABLE 1. Nearest neighbor analysis of calling males during eight sampling nights, with the Clark and Evans method and with the Thompson’stest. The sampled area varied slightly between nights. rA: 2 = 2Nk, kth neighbor. * p < 0.05.

Date NMale

density(1/m²)

rA (m)Clark and Evans

ThompsonNearest neighbor Second neighbor

R c Pattern 2 Pattern 2 Pattern13-June 14 0.0257 3.52 1.13 0.92 Random 43.9 Random 288.5* Regular14-June 5 0.0092 20.76 3.97* 12.7 Regular 181.7* Regular 116.9* Regular16-June 16 0.0253 5.73 1.82* 6.29 Regular 192.4* Regular 582.9* Regular17-June 11 0.0148 5.98 1.45* 2.89 Regular 67.1* Regular 126.7* Regular20-June 5 0.0104 5.66 1.15 0.65 Random 28.1* Regular 183.7* Regular22-June 15 0.0213 6.39 1.80* 5.71 Regular 556.3* Regular 1110.5* Regular24-June 6 0.0293 4.25 1.45* 2.13 Regular 22.4 Random 118.3* Regular26-June 10 0.0385 4.67 1.83* 5.03 Regular 69.1* Regular 120.6* Regular

Vocal assemblages of Physalaemus fischeri46

were between one and six meters (Fig. 2). The Clarkand Evans index and the Thompson’s test, performed for each observation night, indicated that males dis-tributed themselves regularly in most nights (Table 1).Second nearest neighbor distances varied from 6.7 to 19.6 m (mean ± sd: 13.1 ± 4.9 m), and the analysis performed indicated that second neighbors also dis-tributed regularly all nights (Table 1). The frequency distribution of the nearest neighbor distances also in-dicated non-random spacing, although a fixed mini-mum inter-male distance was not observed (Fig. 2).The results contrast with the graphical impression that males tended to form loose clumps at particu-lar sites (Fig. 1). Qualitatively, males aggregated in pairs, triplets, quartets or loose clusters of up to 11 in-dividuals. Thus, the tests detected the arrangement of males within particular clusters but could not detect the clusters themselves. Results from both tests agree for most nights except for June 20 (Clark and Evans:random; Thompson: regular) and June 24 (Clark and Evans: regular; Thompson: random). A positive as-sociation was detected between R and neighbor dis-tances (Spearman rs = 0.72, p = 0.04), indicating that regular spacing is associated with spatial segregation among males. No association was found between Rand male density (Spearman rs = -0.12, p > 0.10).

DISCUSSION

Site tenacity and the regular distribution of males suggest that breeding aggregations of P. fischeri are structured, despite the fact that they are transient.

Qualitatively, males preferred certain areas in the sur-veyed site. However, on a small scale, males tended to space themselves regularly, often no closer than 0.70 m apart and not farther than 6 m. This occurred despite the fact that males did not defend the calling sites (i.e., did not exclude other males aggressively from their calling positions) and site attachment was not long lasting. Thus, male aggression is not neces-sary for prolonged site attachment, and the latter is not a prerequisite for the existence of structured vo-cal assemblages in P. fischeri. In addition, these re-sults suggest that maintenance of a certain distance between males, as well as occupation of a stable posi-tion over short periods, may be advantageous.

Occupancy of the same position over one or sev-eral days has been observed in several territorial and non- territorial anurans, and can be related to advan-tages in sound transmission (e.g., Narins and Hurley, 1982; Wells and Schwartz, 1982), male-male compe-tition (Davis, 1987; Brenowitz and Rose, 1994; Mar-shall et al., 2003), female paths (Grafe, 1997), search strategies of females (Murphy and Gerhardt, 2002), female attraction or choice (Bradbury and Gibson,1983; Grafe, 1997), or site-specific features (vegeta-tion cover, water temperature, predation risk). Thereason why P. fischeri males chosed and returned to the same positions was not obvious and deserves fur-ther investigation. Transmission of P. fischeri calls is currently under study. Preliminary results indicate that there is significant variation in the quality of propagated calls between the main habitats found at Masaguaral, but no differences have been found be-tween locations within a habitat (unpubl. data). Thus,transmission advantages could be related to habitat preferences but are not likely to explain site selec-tion and fidelity. High site fidelity is a component of territoriality, but territoriality also involves defense of a limited resource or exclusive use of an area for prolonged periods. By either definition, P. fischerimales are not territorial because male aggression is uncommon (Tárano, 2007) and aggressive calls have not been described, as far as I know. Observationsof the mating behavior of P. fischeri males and fe-males also indicate that calling sites do not contain re-sources for reproduction, because oviposition occurs at another site, away from the male calling position. Physalaemus fischeri males may have what Wilson (1975) called floating territories (i.e., areas occupied by animals that maintain individual distances with their neighbors for short periods of time).

Non-random spacing has been observed in many anurans (e.g., Brenowitz et al., 1984; Telford, 1985;

FIGURE 2. Distribution of nearest neighbor distances between calling males over sixteen nights of observation. Numbers indicate distance ranges, for instance, 0 corresponds to the interval [0, 0.99], 1 corresponds to [1, 1.99], 2 corresponds to [2, 2.99] and so on.

Tárano, Z. 47

Wilczynski and Brenowitz, 1988; Gerhardt et al.,1989) and can result from availability of suitable reproductive positions, arbitrarily fixed (innate, pre-programmed) distances or male interactions (physi-cal or acoustic). Since P. fischeri males call from shallow water that accumulates in small depressions within and in the periphery of flooded areas, I do not expect these puddles to be regularly distributed. Oth-er authors have failed to find a relationship between site availability and male distribution (e.g., Wilczyn-ski and Brenowitz, 1988). Physical combat provides a way for male spacing but entails potentially high costs; therefore male spacing is likely to be mediated by signals. Acoustic signals usually contain cues that correlate with sender position and with the distance between sender and receiver as, for instance, call am-plitude, degradation of temporal traits or differential attenuation of call frequencies (Wiley and Richards,1978; Brenowitz, 1986). Call amplitude is the cue that better explains male spacing in anurans and insects (review in Gerhardt and Huber, 2002), but the way neighbor call amplitude affects male spacing varies among species. Males may position themselves so that the amplitude of the neighbor’s calls is slightly above their auditory threshold (Römer and Bailey,1986), or space themselves so that the amplitude is about a specific value (Wilczynski and Brenowitz,1988; Gerhardt et al., 1989). In either case, variation of inter-male distances must be higher than variation of the amplitude of the neighbor’s call at the posi-tion of a male. This prediction has been corroborated in several studies (Wilczynski and Brenowitz, 1988; Brenowitz, 1989; Gerhardt et al., 1989; Gerhardt and Huber, 2002). On the contrary, when spacing results from arbitrarily fixed innate preferences, variation of inter-male distances must be low. In the present study, the variation of inter-male distances was high (44-55%) and, in addition, there was a positive re-lationship between R and nearest neighbor distances (see also Pseudacris crucifer, Gerhardt et al., 1989; Ololygon rubra, Bourne, 1992; and Eleutherodacty-lus johnstonei, Ovaska and Hunte, 1992). Both find-ings are suggestive that male spacing in P. fischeriresults from acoustic cues.

The Clark and Evans’ and the Thompson’s tests agreed for most of the nights. Discrepancies between tests cannot be attributable to biases inherent to each one, because most of them are related to boundary problems (Donnelly, 1978; Sinclair, 1985). Theseproblems were avoided in the present study by per-forming all-individuals sampling and also because there is an ecological limit to male distribution (i.e.,

the boundary of the flooded area). Thus, no males were calling outside the sampled area. Campbell(1990) also reported discrepancies in the results when the tests were performed on data that contained com-ponents of aggregation and regularity. The author concluded that, when there are two modes of spac-ing, these tests may not yield appropriate results. OnJune 20 only five males were active, four of which were aggregated (mean sd = 1.98 0.26 m) and one which was farther away (> 10 m). When this male was removed, both tests indicated aggregation. Thus,biases related to the differential effect of sample size, non-independence of data when males are each oth-er’s closest neighbors and combined patterns of dis-persion could explain the discrepancy.

In conclusion, P. fischeri males form stable, al-though short-term, aggregations, because males show site fidelity during several consecutive nights and space themselves within the aggregation. Male seg-regation is suggestive of acoustically mediated spac-ing, but this remains to be investigated. The results of this study are particularly interesting given that the rain patterns force males to vary their distribu-tion from night to night. Despite this, males attach to specific calling positions and space themselves in the aggregations.

RESUMEN

Las agregaciones reproductivas son comunes en los anuros. En ellas, los machos pueden distribuirse aleatoriamente o distanciarse de alguna manera, así como ocupar o no la misma posición a lo largo de una noche o de noches consecutivas. Se investigaron los patrones de distribución y la fidelidad espacial de los machos de Physalaemus fischeri en un bajío de arbus-tos moderadamente inundado en una localidad de los llanos centrales de Venezuela. Para ello se determinó la posición de los machos y la distancia al vecino más cercano durante 21 noches consecutivas. Se localiza-ron 35 machos en 53 posiciones de canto. No todos los machos estuvieron activos simultáneamente. Die-cinueve machos fueron observados en la misma po-soción durante varias noches, consecutivas o no. Elnúmero de noches consecutivas en una misma poso-ción fue 2,59 ± 1,12 (promedio ds; max = 5 noches, N = 17 machos) y el número total de noches (conse-cutivas y no consecutivas) fue 3,00 ± 1,41 (max = 6noches, N = 15 machos). La distancia al vecino más cercano más frecuente fue 2,5 m, y cerca de 58% de las distancias fueron inferiores a 6 m. El índice de Clark

Vocal assemblages of Physalaemus fischeri48

y Evans (R) y la prueba de Thompson, indicaron que los machos se distribuyeron regularmente la mayoría de las noches. Se encontró asociación positiva entre R y la distancia al vecino más cercano (Spearman rs = 0,72, p = 0,04), lo cual indicó que la regularidad espacial estaba asociada con la segregación (distan-ciamiento) entre los machos. Los resultados indican que los machos de P. fischeri forman agregaciones dinámicas pero organizadas, porque los machos se separan entre si y son fieles a sus posiciones, aunque por poco tiempo. La dispersión regular sugiere que la segregación está mediada acústicamente, porque los enfrentamientos entre machos son raros. Además,se presume que la segregación y la fidelidad espacial pueden conferir ventajas reproductivas a los machos que deberán ser investigadas.

ACKNOWLEDGEMENTS

I dedicate this paper to the memory of T. Blohm, for his friend-ship and continued support at Fundo Pecuario Masaguaral since 1987. I am very grateful to J. G. Acosta for logistic support in the field and to M. J. Ryan and C. Gómes-Parisca for their comments on the manuscript. This study was supported by FONACIT (S1 2002000276). The study was conducted according to local laws for wildlife research (Scientific License granted to Z. Tárano by Ministerio del Poder Popular para el Ambiente y los RecursosNaturales, Dirección de Biodiversidad).

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Submitted 12 August 2008Accepted 25 February 2009

Vocal assemblages of Physalaemus fischeri50