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Spatial niche variation in two sympatricspecies of Bokermannohyla (Anura:Hylidae) in southeastern BrazilNathália Gonçalves da Silva Lima a , Raphael Costa Leite de Limaa , Juan Espanha Moreira Dias a , Priscilla Ferreira Torres a & PaulaCabral Eterovick aa Programa de Pós Graduação em Zoologia de Vertebrados,Pontifícia Universidade Católica de Minas Gerais , Belo Horizonte ,BrazilPublished online: 13 Aug 2013.

To cite this article: Journal of Natural History (2013): Spatial niche variation in two sympatricspecies of Bokermannohyla (Anura: Hylidae) in southeastern Brazil, Journal of Natural History, DOI:10.1080/00222933.2013.802044

To link to this article: http://dx.doi.org/10.1080/00222933.2013.802044

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Journal of Natural History, 2013http://dx.doi.org/10.1080/00222933.2013.802044

Spatial niche variation in two sympatric species of Bokermannohyla(Anura: Hylidae) in southeastern Brazil

Nathália Gonçalves da Silva Lima, Raphael Costa Leite de Lima, Juan EspanhaMoreira Dias, Priscilla Ferreira Torres and Paula Cabral Eterovick*

Programa de Pós Graduação em Zoologia de Vertebrados, Pontifícia Universidade Católica deMinas Gerais, Belo Horizonte, Brazil

(Received 17 September 2012; final version received 24 April 2013)

We studied patterns of microhabitat use by adults of two sympatricBokermannohyla species at the Reserva Particular do Patrimônio NaturalSantuário do Caraça, southeastern Brazil. We selected three streams, one whereboth species occurred in syntopy and the other two where each one occurredalone. We sampled 150-m transects in each stream throughout 1 year, recordingmicrohabitat features for each frog located (substrate type, height and distance fromwater). Microhabitat availability varied between dry and wet seasons in all streams,and overall microhabitat diversity changed in two streams. Bokermannohylananuzae seemed to have a niche contraction in the presence of Bokermannohylamartinsi, but this only happened during the dry season. Microhabitat requirementsduring the wet season may be closely linked to similar reproductive needs thatprobably represent a strong selective pressure, forcing niche overlap.

Keywords: Bokermannohyla nanuzae; Bokermannohyla martinsi; syntopy;microhabitat use; niche overlap

Introduction

The role of a particular species in a community is based on a pattern of resource useand interactions with other species, including some that use the same resources. Suchpatterns of resource use are the focus of the niche theory that divides the resourcesused by a species into three main dimensions: food, space and time (Hutchinson 1957;Pianka 1973; Putman 1994). These dimensions can be further divided into type andsize of food, macrohabitat and microhabitat, and daily and annual periods of activity,respectively (Schoener 1974). Differences between species regarding these dimensionsmay facilitate their co-existence (Pianka 1973). There may be an importance hierarchyrelated to niche dimensions for some vertebrates and invertebrates, but the dimen-sions are usually related to each other (Schoener 1974; Nakagawa et al. 2012). Whensympatric species have high niche overlap, character displacement may occur whenindividuals within the population that show less overlap with those of the other speciesare selectively favoured (Rice et al. 2009).

Sympatric species often differ in microhabitat use (Gorman and Haas 2011; Lisicicet al. 2012; Poindexter et al. 2012). In anuran amphibians, microhabitat selection mayresult from several factors such as responses to seasonality (Eterovick et al. 2010a,

*Corresponding author. Email: pceterovick@gmail.com

© 2013 Taylor & Francis

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2 N.G.S. Lima et al.

2010b), specific needs during the breeding period (Afonso et al. 2007a; Wachlevskiet al. 2008), and food availability (Warkentin 1992). Meanwhile, the presence ofpredators (Kopp et al. 2006), morphological features, natural history (Crump 1971;Caldwell 1996; Bertoluci and Rodrigues 2002), diseases, dispersion ability and com-petition (Parris 2004) are all biological processes that contribute to species spatialdistribution.

Anurans are frequently associated with moist areas such as streamside habitats,where they can explore different microhabitats, and even closely related species maydiffer in microhabitat choices (Eterovick et al. 2010b). Some Bokermannohyla species,for instance, perch on rocks (Bokermannohyla feioi; Napoli and Feio 2006) or onbranches hanging over the water at streamside habitats (Bokermannohyla sazimai;Napoli 2000), whereas others prefer epiphytic bromeliads (Bokermannohyla astartea;Napoli 2000) that store water in their leaves (Rocha et al. 2004).

Bokermannohyla martinsi and Bokermannohyla nanuzae (Hylidae) are sympatric(and syntopic at some streams) at the RPPN Santuário do Caraça, a private naturalreserve in southeastern Brazil, offering a suitable scenario to test whether the same eco-logical conditions moulded differentiated habits in these congeneric species or if theirphylogenetic relationship dictate their ecological features. Bokemannohyla nanuzae isincluded in the Bokermannohyla circumdata species group with 14 other species thathave dark vertical stripes on the flanks and hypertrophied prepollex in adult males(Napoli 2000). Bokemannohyla nanuzae’s known distribution includes other localitiesin the Espinhaço mountain range in Minas Gerais state, southeastern Brazil (Serrado Cipó; Eterovick and Sazima 2004; Serra do Caraça; Afonso et al. 2007b, andParque Estadual do Rio Preto; Leite et al. 2006). It breeds in permanent streams withrocky bottoms surrounded by gallery forests (Eterovick and Sazima 2004). It is noc-turnal and, at Serra do Cipó, males were observed to call from October to February,usually on trees or shrubs (or, sometimes, bromeliads) at the streamside vegetation,1.5–4 m from the ground (Eterovick and Sazima 2004). The breeding period can belonger, as was recorded at the RPPN Santuário do Caraça (Afonso et al. 2007b).Bokermannohyla circumdata also occurs at the RPPN Santuário do Caraça, althoughit is rare compared with the other two species of Bokermannohyla (Afonso et al. 2007a;personal observation).

Bokermannohyla martinsi is included in the Bokermannohyla martinsi species group(Faivovich et al. 2005) and occurs in rocky meadows, usually associated with rockyoutcrops at open areas, but individuals can occasionally be found at streams sur-rounded by gallery forests (Napoli 2000) in highlands of south and southeastern Brazil(Bokermann 1964).

In this study we aimed to investigate how B. martinsi and B. nanuzae use the spacewhen occurring in syntopy or at distinct sites. We aimed to (1) compare microhabitatavailability among studied streams and throughout the year at each stream, (2) iden-tify and compare microhabitats preferred by each species when in syntopy or isolated,(3) estimate habitat heterogeneity and niche breadth of both species in the studiedstreams, (4) estimate and compare overlaps of B. nanuzae niches between seasons(wet versus dry) and among streams, and (5) infer whether patterns of microhabitatuse of B. nanuzae and B. martinsi in syntopy indicate homology or niche partition-ing. We expected the two species to show high niche overlap if homology were thedetermining factor moulding their spatial niche.

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Journal of Natural History 3

Material and methods

Study siteThe Espinhaço mountain range extends through the states of Minas Gerais andBahia in east Brazil (Derby 1966), representing a contact zone among the AtlanticForest, the Cerrado and the Caatinga, three important Brazilian biomes (Giuliettiet al. 1997). The first two are also biodiversity hotspots (Myers et al. 2000; Silvaand Bates 2002; Tabarelli et al. 2005) with high amphibian endemism (93% of thespecies for the Atlantic Forest; Duellman 1999; 30% for the Cerrado; Silva and Bates2002).

The Reserva Particular do Patrimônio Natural (RPPN) Santuário do Caraça,where we conducted this study, has an area of 10,188 ha and represents a transitionbetween the Atlantic Forest and the Cerrado (Giulietti and Pirani 1988; Giulietti et al.1997), in the southern portion of the Espinhaço mountain range, Catas Altas munic-ipality (20◦05′ S, 43◦29′ W), Minas Gerais state, Brazil. Altitudes vary from 850 to2070 m above sea level, the climate has a dry season from April to September and awet season from October to March, and annual temperature ranges from 13◦C to 29◦C(Viveros 2010).

Sampling proceduresWe selected four independent (not connected) streams that flow into Caraça river toconduct the study. At the first stream (Stream 1) both B. martinsi and B. nanuzaewere present, at the second (Stream 2) just B. martinsi was present, and at the third(Stream 3) just B. nanuzae was present (Figure 1, Table 1). We sampled Streams 1 and3 for 3–4 days every month and Stream 2 for 3–4 days every 2 months from August2010 to April 2012. We sampled a fourth stream where just B. martinsi was presentin the months when we did not sample Stream 2, but we eliminated this other streamfrom the analyses because of a very small sample size. We did not record B. circumdatain the streams we studied, except for a single individual in the stream that was excludedfrom the study.

At each stream, we covered a 150-m section looking for frogs using visual searchaided by auditory search to help locate calling males (Heyer et al. 1994). We followedthe 150-m stream section as a transect, its width varying according to the presenceof potential frog habitats (flooded areas, rocky outcrops, bromeliads), positioning ofcalling males, and stream morphometry. We detected all frogs within 2 m of the water,so we determined transect width as 2 m from the water at each side of the stream (andquantified microhabitat availability accordingly, see “Microhabitat data collection andanalyses” section).

We measured frogs’ snout–vent length (SVL) with callipers (to the nearest 0.5 mm).We determined the sex of sampled frogs based on vocalization or developed prepollexin males and visible eggs at the abdomen of females. We considered as females thosefrogs that were the same size or bigger than the smallest individual confirmed as anadult male but that lacked a prepollex. Smaller individuals were considered to be youngand not included in our analyses.

We killed voucher specimens with 20% benzocaine, preserved them according toHeyer et al. (1994), and deposited them in the Herpetology Collection of the Museude Ciências Naturais of the Pontifícia Universidade Católica de Minas Gerais.

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4 N.G.S. Lima et al.

Figure 1. Map showing the location of the RPPN Santuário do Caraça and the three streamswhere we sampled microhabitat use by Bokermannohyla nanuzae and Bokermannohyla martinsi.

Microhabitat data collection and analysesFor each individual frog found we recorded the type of substrate where it was posi-tioned as (1) rock with mosses, (2) bare rock, (3) green leaves (including ferns,bromeliads, grass, leaves on trees or shrubs), (4) branches (including also deadbranches, lianas, roots), (5) sand/dirt, (6) leaf litter, (7) moss tufts on the ground,or (8) water. We grouped bromeliads with green leaves because we only found threefrogs (B. nanuzae) using them as perching substrates and did not observe them usingphytotelmata in the bromeliads. We also recorded height from the ground and theclosest horizontal distance from water (to make sure that all frogs considered wereinside the established transect width). Repeated records of the same individual might

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Journal of Natural History 5

Table 1. Characterization of streams sampled for microhabitat use by adult individuals ofBokermannohyla martinsi and Bokermannohyla nanuzae at the RPPN Santuário do Caraça,southeastern Brazil.

Streams Coordinates Description Species present

1 20◦05′51′′ S43◦29′56.6′′ W

Section of a third-order stream (sensuStrahler 1957) downstream from asmall waterfall called “Banho doBelchior”, open to tourist visitation.The stream bottom is rocky,irregular, with emergent rocks.

B. nanuzaeB. martinsi

2 20◦06′23′′ S43◦28′28′′ W

Section of a third-order stream (sensuStrahler 1957) encompassing foursmall waterfalls intertwined with fourbackwaters and called “Cascatinha”.It is also open to tourist visitation.The stream bottom is rocky,irregular, with emergent rocks.

B. martinsi

3 20◦03′27′′ S43◦30′13′′ W

Section of a third-order stream (sensuStrahler 1957) with difficult accessand not visited by tourists. Thesection is a succession of backwatersand riffles.

B. nanuzae

have occurred occasionally in different months, but we consider this possibility to besmall. From August 2011 until the end of this study, some frogs were collected foranother study after microhabitat characterization (N.G.S. Lima et al., unpublisheddata): we collected 14 individuals of B. nanuzae and 11 individuals of B. martinsi atStream 1, five individuals of B. martinsi at Stream 2, and 44 individuals of B. nanuzaeat Stream 3, which, in most cases, represented a small proportion of our sample sizesin the present study. The frogs collected were well distributed among months, onlyin three instances more than five frogs were collected at a stream in 1 month (n = 7,9 and 10 B. nanuzae). These values were proportional to frog abundance at the site inthe given month, and we never noticed frog abundance to be reduced after collectingindividuals. Both species studied have prolonged breeding (N.G.S. Lima, unpublisheddata), and not all individuals call at the same time, so we believe that removing someindividuals from the population will not affect the pattern of microhabitat use, but willreduce the chances of pseudoreplication.

To estimate microhabitat availability in the studied stream sections, we recordedpresence of the same eight types of substrates at three height classes (0–70 cm,>70–140 cm and >140 cm) at 50 points evenly distributed (spaced by 3 m) along the150-m transect. These points were established at five distances from the water (0, 0.5,1.0, 1.5 and 2.0 m) sequentially, alternating stream margin every time the sequence wasre-started. Parts of the stream transect with higher microhabitat heterogeneity wouldtherefore result in higher numbers of records of available microhabitats (Oliveira andEterovick 2010). The combination of substrate types and height classes resulted in24 possible microhabitat types, from which 20 were actually recorded (see Table 2)

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6 N.G.S. Lima et al.T

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Journal of Natural History 7

and used to compare microhabitat use and availability. We estimated availability ofmicrohabitat types both in the dry (July 2011) and wet (January 2012) seasons tocompare them and test for possible seasonal variations in each stream with G-test(chi-square test assumptions were not met; Ayres et al. 2007). We also comparedstreams within each season to account for possible influence of differences amongstream microhabitat availability in our results. To ensure that collection of individu-als during the study did not affect the pattern of microhabitat use, we compared dataof B. nanuzae at Stream 1 (for which we had enough records) from the same monthssampled in different years, both before and after we started collecting. We controlledfor Type I error using Bonferroni correction (Rice 1989).

To identify preferred microhabitats, we calculated Electivity (D) according toJacobs (1974), considering availability (Pk) and use (Rk) of each type “k” ofmicrohabitat by each species with the formula:

D = (Rk − Pk) / [(Rk + Pk) − (2RkPk)] ,

where Rk = proportion of microhabitat “k” in all records of microhabitats used bythe species and Pk = proportion of microhabitat “k” in all records of microhabitatavailability in the stream. The values of D ranging from + 1 (meaning the strongestpreference for microhabitat “k”) to – 1 (meaning total rejection for microhabitat “k”,i.e. it is never used by the species), whereas 0 means microhabitat “k” is used with thesame proportion as its availability in the environment.

We also estimated microhabitat diversity for each stream in each season (wet anddry), and diversity of microhabitats used by each species as a measurement of itsniche breadth. We used Hulbert’s PIE index in the software ECOSIM (Gotelli andEntsminger 2001):

PIE = (N/N − 1)(1 − �Pi2) ,

where Pi represents proportion of microhabitat “i” in the total set of records ofmicrohabitat use by the species (N) for estimating species niche breadth, or propor-tion of microhabitat “i” in the total set of records of microhabitat availability in thestream (N) for estimating habitat heterogeneity (i.e. diversity of microhabitats) in thestream.

First, we compared each stream between seasons and compared the three streamswith each other within each season to test for differences in habitat heterogeneity.Second, we tested whether the species changed their niche breadth between seasonsor among streams. We tested for statistical significance based on 1000 simulations inthe software ECOSIM (Gotelli and Entsminger 2001).

Using Pianka’s (1973) niche overlap index (Ojk) with the RA3 randomization algo-rithm in the software ECOSIM (Gotelli and Entsminger 2001), we compared the use ofmicrohabitat types by B. nanuzae between seasons at Stream 3 and between the twostreams where it occurred (Streams 1 and 3) using data from the wet season, when thespecies was the most abundant. We compared males and females at Stream 3, wherewe had more records of females (n = 13) using the same test to check for differencesbetween sexes. We tested for statistical significance based on 1000 simulations. We didnot perform these same analyses for B. martinsi because there were not enough data.We also compared niche overlap between the two species in Stream 1.

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8 N.G.S. Lima et al.

Results

From August 2010 to April 2012 we obtained 179 records of microhabitat use forB. nanuzae and 33 records for B. martinsi (Table 2). For microhabitat availability esti-mates, we obtained 1228 records of available microhabitats for Stream 1, 1249 forStream 2 and 1479 for Stream 3 considering both seasons (Table 2).

Microhabitat availability varied significantly between dry and wet seasons inthe three streams studied (Stream 1: G = 234.9, p < 0.0001, df = 19; Stream 2:G = 134.44, p < 0.0001, df = 19; Stream 3: G = 160.9, p < 0.0001, df = 19). Thestreams also differed from each other both during the dry (G = 468.55, p < 0.0001,df = 38) and the wet (G = 716.04, p < 0.0001, df = 38) seasons. Microhabitats usedby B. nanuzae at Stream 1 before we started collecting some individuals did not differfrom microhabitats used after collecting (G = 14.11, p = 0.227, df = 11).

Bokermannohyla nanuzae used branches preferentially during the dry season,whereas during the wet season this species also used rocks (at various heights, with orwithout moss) at Stream 1. At Stream 3, besides these microhabitats, the species alsoused rocks during the dry season, leaves during the wet season, and sand/dirt duringboth seasons. Bokermannohyla martinsi preferred rocks at Stream 1, and at Stream 2 italso used branches more than expected, as well as rocks.

Microhabitat heterogeneity (given by diversity of microhabitats available) var-ied between seasons in two of the three studied streams (Table 2). Stream 1 hadincreased habitat heterogeneity in the wet season, whereas Stream 2 had increasedhabitat heterogeneity in the dry season. The three streams differed during the wet sea-son, whereas only Stream 1 differed from Streams 2 and 3, which were similar to eachother, during the dry season (Table 2).

For B. nanuzae, niche breadth was narrower during the dry season at Stream 1,but niche breadths did not differ between seasons at Stream 3, nor between Streams1 and 3 during the wet season (comparison made by standardizing sample size to ninerecords of microhabitat use, the smallest sample size; see Table 2). We pooled male andfemale data because we found sexes to overlap more than expected in microhabitat use(Ojk = 0.742; p = 0.03 for observed > simulated at Stream 3). We only compared nichebreadths of Bokermannohyla martinsi between streams during the wet season, becausesample sizes were very small for this species during the dry season (Table 2). Nichebreadth was wider at Stream 2 than at Stream 1, where B. martinsi occurred in syntopywith B. nanuzae.

Realized niche overlap was higher than expected for B. nanuzae between seasonsat Stream 1 (Ojk = 0.912, p < 0.001), and also between Streams 1 and 3 in the wetseason (Ojk = 0.911, p < 0.001). The two species did not overlap in microhabitat usemore than randomly expected (Ojk = 0.464, p = 0.512) at Stream 1.

Discussion

The spatial dimension of species’ niches is frequently moulded by competitive interac-tions, when sympatric species go through niche shifts as an evasive strategy to avoidcompetition (Rice et al. 2009; Lisicic et al. 2012). For such mechanisms of niche diver-gence to be possible, plasticity in resource use is an important characteristic for thespecies involved (Hunt and Bonsall 2009). Plasticity in resource use (or broader niches)is also important for species that cope with unstable environments (Levins 1968). The

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variations we observed in microhabitat availability among streams and also temporalvariations in a given stream throughout the year indicate a spatially and temporallydynamic distribution of microhabitats that will require species to adjust their spatialand/or temporal distribution to use their preferred microhabitats where and when theyare available. This means the studied species of Bokermannohyla must show at leastsome plasticity to cope with their dynamic habitats.

It is interesting to notice that rocks were preferred microhabitats for B. nanuzaeat Stream 3 in both seasons, whereas in Stream 1, where B. martinsi was present andoccupied rocks preferentially, B. nanuzae used rocks less frequently or even avoidedthis microhabitat. The spatial niche of B. nanuzae was significantly reduced at Stream1, where it occurred in syntopy with B. martinsi; however, it just happened during thedry season. Microhabitat diversity was reduced in the dry season in this stream, butthe amount of rocks with moss was almost the same in both seasons at all heights(data not shown). Although we did not record B. nanuzae using bare rocks higherthan 70 cm in the dry season, lower rocks also had similar abundances in both seasons(data not shown) and markedly different electivities (see Table 2). Hence, the changein microhabitat preferences of B. nanuzae is not likely to be caused by a reduction inthe availability of rocky substrates. On the other hand, the spatial niche of B. mar-tinsi was significantly narrower in Stream 1 than Stream 2, where B. nanuzae wasnot present. Although we could not find other streams with large numbers of boththese frogs in syntopy and isolated to confirm the hypothesis of niche contraction dueto competition, our results are indicative of some influence of these two species ofBokermannohyla on each other.

Bokermannohyla nanuzae had a higher variety of microhabitats that were usedmore than would be expected at random, whereas B. martinsi was more restrictivein its choices (Table 2). When in syntopy with B. martinsi, B. nanuzae seemed tocontract its realized niche, avoiding the use of rocks, where B. martinsi preferred toremain. However, this pattern was more evident during the dry season, whereas dur-ing the wet season both species showed a preference for rocky microhabitats, wheremales positioned themselves to call and wait for females. We observed young frogs andnon-breeding adults of B. nanuzae perching on herbaceous vegetation or bromeliads,whereas calling males preferred rocks close to previously chosen sites for egg layingin the water (N.G.S. Lima, unpublished data). Male frogs are likely to remain close tofemale oviposition sites, but they can also search for microhabitats that reduce preda-tion risk (Gorman and Haas 2011). Differences in microhabitat use by gecko specieswere also reported to be dependent on season and age (Lisicic et al. 2012).

Apparently the two species tolerate higher niche overlap during the breedingperiod, maybe because their close relationship reflects a common adaptation to callfrom similar microhabitats. Microhabitat use by adult frogs was shown to have a phy-logenetic signal, as opposed to microhabitat use by tadpoles (Eterovick et al. 2010b).For instance, the use of branches and leaves by B. nanuzae was also observed byAfonso and Eterovick (2007a) at the RPPN Santuário do Caraça and by Oliveiraand Eterovick (2010) at another locality further north in the Espinhaço mountainrange. Frog calling sites may be associated with breeding microhabitats that includeegg laying and tadpole development sites (Zimmerman and Simberloff 1996). Underthese circumstances, historical factors may assume greater importance than compet-itive interactions to determine species distribution (Inger et al. 1974; Zimmermanand Simberloff 1996). On the other hand, the studied species may show some niche

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displacement during the dry season, which might avoid competition for other resourcessuch as food. Adjustments in other niche dimensions may avoid competition for foodin species with similar requirements (Nakagawa et al. 2012), unless the supply of foodis unrestricted (Yamada and Kumagai 2012).

Two sympatric and closely related species of Lithobates (Lithobates clamitansclamitans and Lithobates okaloosae) were shown to select microhabitats with differ-ent features in syntopy (Gorman and Haas 2011). Although their different sizes arelikely to preclude them from competing for resources, hybridization has already beenrecorded between them, which may justify spatial differentiation at the microscale(Gorman and Haas 2011). Bokermannohyla martinsi (whose males reach 64 mm SVL,Bokermann 1964), is 1.5 times larger than B. nanuzae (SVL = 42 mm, Bokermannand Sazima 1973) a size difference corresponding with that between L. c. clamitansand L. okaloosae (Gorman and Haas 2011). However, hybridization or interspecificamplexus were never observed between these Bokermannohyla species during a studyon their reproductive behaviour at the same streams at the RPPN Santuário do Caraça(N.G.S. Lima et al., unpublished data). During the present study, we observed malesof both species calling close to each other and on the same nights, so perhaps theirdifferent calls (Bokermann and Sazima 1973; N.G.S. Lima, unpublished data) provideenough cues for females to successfully locate co-specific males.

Spatial segregation may occur on macro (localities), meso (bodies of water) ormicro (microhabitats within bodies of water) scales (Gorman and Haas 2011). In thecase of B. nanuzae and B. martinsi, all three scales may contribute to the avoidance ofniche overlap. The two species occur in both sympatry and allopatry throughout theirdistribution (Leite et al. 2008). When in sympatry, they may be syntopic or segregatedin streams (present study), and when syntopic, they may show some level of nichedisplacement. However, when it comes to use of microhabitats related to breedingactivities, historical factors seem to play a stronger role and both species will tolerate ahigher level of niche overlap, maybe avoiding hybridization through their differentiatedadvertisement calls.

Acknowledgments

We are grateful to R.C.C. Souza, A.S.B. Gontijo, M.R.J. Corrêa, G.C. Conrado, V. Borges, R.C.Pires and M.G. Brandão for help during field work, to the staff of the RPPN Santuário doCaraça for permits and logistics, the Instituto Brasileiro do Meio Ambiente e dos RecursosNaturais Renováveis for a permit (23773–1), and the Fundação de Amparo à Pesquisa doEstado de Minas Gerais (Fapemig) for financial support. A scholarship was awarded to N.S.G.Lima by the Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES) andA Research Productivity grant (301077/2010-0) was given to P.C. Eterovick by the ConselhoNacional de Desenvolvimento Científico e Tecnológico (CNPq).

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