Comparison of anuran acoustic communities of two habitat types in the Danum Valley Conservation Area,

Sabah, Malaysia

Abstract. We compared advertisement calls of frog assemblages in two different habitats, (i) an Open area along a dirt road with ponds and secondary vegetation; (ii) a fast flowing stream in primary forest. Eleven frog species were recorded and significant differences in the dominant call frequencies between the two observed frog communities were discovered. Stream-breeding species produce higher frequencies than species occurring in the roadside habitat. Noisy habitats have an influence on dominant frequency and demand acoustic adaptations to increase the signal-to-noise ratio. Selective logging represents a major threat to stream-breeding anurans in Sabah. Pollution of clear water threatens the stream-dependent herpetofauna.

SALAMANDRA

Keywords. Amphibia, Anura, conservation, vocalisation, Malaysia.

129-138

Introduction

43

Selective logging has been the main cause of disturbance to tropical forests in Southeast Asia (MARSH & GREER 1992, WILLOTT et al. 2000). Concession-based timber extraction and plantation establishment result in high- ly fragmented forests (MCMORROW & TAL- IP 2001, CURRAN et al. 2004) and increase river sediment yields (DOUGLAS et al. 1993). The extent to which biodiversity is altered in selectively logged forest is an important conservation issue. Fragmentation, degrada- tion and conversion of rainforests affect the tropical herpetofauna (ALCALA et al. 2004). About half the frog species in Southeast Asia are restricted to riparian habitats and devel- op in streams (INGER 1969, ZIMMERMAN & SIMBERLOFF 1996). Most anuran stream-side communities in Borneo are known to breed in clear, turbulent water and are absent in streams with silt bottoms and lacking riffles and torrents (INGER & VORIS 1993). Several anuran community studies have focused on environmental conditions such as vegeta- tion, elevation, rainfall and microhabitat (IN-

1 Rheinbach, 20 August 2007

GER 1969, DUELLMAN 1978, INGER & VORIS 1993, GILLE~PIE et al. 2004). Apart from be- havioural and morphological adaptations to the environment, frog assemblages also show acoustic differences. A prime factor sepa- rating species within anuran assemblages is vocaiization (DUELLMAN & TRUEB 1986). Acoustic partitioning through temporal and spectral features minimizes competition and allows conspecific females to recognize indi- vidual signalling males (HÖDL 1977, GARCIA- RUTLEDGE & NARINS 2001, GERHARDT 8r

HUBER 2002). The dominant frequency of a frogS call is partially constrained by its body size (KIME et al. 2000). Snout-vent length and dominant frequency are negatively correlated (LITTLEJOHN 1977, DUELLMAN & PYLES 1983, RYAN & BRENOWITZ 1985). Sounds produced by waterfalls and fast-flowing streams con- tribute to the ambient noise level. Distinct, acoustic habitat properties ("melotops") de- mand different adaptations on animal vocal- izations. In this study, species composition was determined for two habitats within the Danum Valley Conservation Area (DVCA), a fast flowing stream in the primary forest

ISSN 0036-3375

0 2007 Deutsche Gesellschaft für Herpetologie und Terrarienkunde e.V (DGHT) http:llwww.salamandra-journal.com

INGER et al.

and a roadside habitat with secondary veg- etation, and spectral and temporal features of the acoustic signals were compared.

Material and methods Study area

From 10 January to 13 March 2006, we studied frog communities in DVCA, Sabah, Malaysia. DVCA has an area of 43,800 ha of lowland tropical rainforest and is located in the upper catchment area of the Segama River. The Da- num Valley Field Centre (DVFC) is located on the Western edge of the DVCA (4'57'40'' N, ii7"48'oon E; all but 9% of the area is below 760 m above sea level) from where a 2.8 km long trail leads south to the Tembaling water- fall. The rainy season in Sabah extends from December to March (Northeast Monsoon) with rainfall peak during February (monthly total 788 m i ) . Annual precipitation is near 3,000 mm with year-to-year fluctuation of about ioo mm. Mean annual temperature is 26.7"C with mean maximum 30.9"C and mean minimum 22.5"C. Daily temperature fluctuations are noticeably more pronounced than the year-to-year fluctuations. In the pe- riod from January to March the highest re- corded temperature was 32.5OC and the low- est was 20.3"C; mean relative humidity at the DVFC was 97.0% at 8:ooh and 89.7% at 14:ooh. Daily rainfall and temperature data from January to March 2006 derived from the Danum Valley weather station, which is maintained by the staff of the Royal Society SE Asia Rain Forest Research Programme.

Sampling methods

We focused on two macrohabitat types. One is pristine, the other disturbed. The Tembal- ing River within the primary dipterocarp for- est at about 900 m elevation is a fast flowing freshwater stream with rapids, waterfalls and no siltation. The selected disturbed habitat was along a dirt road in the DVFC with sec-

ondary vegetation, ephemeral roadside pools filling seasonally with water, and varying de- grees of human disturbance. In both habitats iooo m long and y-shaped transects were established and marked with coloured tape. We performed visual and acoustic encounter surveys. The search areas also included adja- Cent riverbanks or vegetation up to a distance of 3 m to the water- or road-edge. Sampling was performed independent of prevailing weather conditions. Each transect was sam- pled at least 20 times by two observers during the day and during nocturnal censuses. Re- peated controls of the Same transect on con- secutive days were avoided to ensure inde- pendence of samples. To determine all call- ing species, a 24-hour time period was sam- pled four times during one month along both transects. After locating a vocalizing male, call recordings were made from distances of i to 5 m using directional and surround mi- crophones (Sennheiser Me 66, AKG D 190 E) and DAT- recorders (Sony DAT-Rec. TCD- D8). Microhabitat temperature and humid- ity were measured with a digital thermohy- grometer (Testo 610 GM) before each record- ing. Frogs were located at their resting sites, and if possible, captured and placed in plastic bags. Snout-vent length and snout-urostyle length were measured using a Wiha calliper (I 0.1 mm). To differentiate between individ- uals we photographed and compared dorsal colour Patterns. All individuals were released after taking their measurements.

Data analysis

We digitized and analysed the recorded calls with the sound-analysis Software Raven 1.2.1

at a sampling frequency of 44.1 Hz and with a mono 16 bit PCM Input and a 10 Hz update rate at normal speed. Power spectra, sono- grams and oscillograms of one to five adver- tisement calls were analyzed for each frog and the average dominant frequency, mini- mum and maximum frequency, call duration, note duration, repetition rate and number of

Anuran acoustic communities in Sabah, Malaysia

notes, when applicable were calculated for each individual. Spectrogram views were produced with a Hann-filter with a sample size of 512 and a 3-dB filter bandwidth of 124 Hz. The correlation between body size (SVL) and dominant frequency was calculated with a Spearman non-parametric correlation (p 5 0.05). ANOVA (p 5 0.05) was used to test for statistical differences, in SVL (mm) and dom- inant frequency (Hz) of advertisement calls, among frog assemblages in two habitats. The influence of SVL and habitat on the dominant frequency of the frog species was calculated by an ANCOVA (p 5 0.05). Since the sample size for some anuran species tested was N = 1, the influence of SVL on dominant frequency was calculated twice: once corrected accord- ing to number of individuals and once with- out correction. All statistical tests were pro-

(Fig. 5), Polypedates otilophus (Fig. 6 ) , and Bufo nsper (Fig. 7), Meristogenys orphnocne- mis (Fig. 8), Microhyla sp. (Fig. g ) , Staurois natator (Fig. io), Staurois latopalmatus (Fig. ii), respectively. No calls could be recorded for species without frequency data (Tab. 1). A total of 213 calls were analyzed. The dominant call frequencies of the anuran species are not dependent on the SVL of the vocalizing in- dividual~ (N = 11; C = -0.555; p < 0.077; r2 = 0.30) (Fig. 13). Meristogenys orphnocnemis, a species found in the stream habitat produced the highest calling frequency (7,205.0 Hz). Frog species from the torrent are above the

duced with SPSS for Mac 11.0.4. ' 01 ' 02 ' 03 ' 0:4 ' 0:s '

Results 15

10

During the sampling period 20 frog species 5

were found. Eleven frog species were record- kHz 0,1 O,Z 0,3 0,4 0,5

ed, six along the disturbed area and five with- in the pristine habitat: Fejervarya nicobarien- 2. 'pectrogram (frequenc~ LkHzI) arid wave-

form (rel. amplitude [kUnit] = proportional to sis 11, Feje""ar~a limflocharis (F&. 2)> pressUre of the recording) of the ahertise. Rhaco~korus 31, P o l ~ ~ e d a t e s ment ca11 of Fejervarya limnocharis. Temperature leucomystax (Fig. 4), Polypedates macrotis during recording 24.6 "C,

Fig. 1. Spectrogram (frequency [kHz]) and wave- Fig. 3. Spectrogram (frequency [kHz]) and wave- form (rel. amplitude [kUnit] = proportional to form (rel. amplitude [kUnit] = proportional to sound pressure of the recording) of the advertise- sound pressure of the recording) of the advertise- ment call and non-collected specimen of Fejer- ment call and non-collected specimen of Rhacoph- varya nicobariensis. Temperature during record- orus dulitensis. Temperature during recording 26.3 ing 25.4 "C. "C.

DORIS PREININGER et al.

Fig. 4. Spectrogram (frequency [kHz]) and wave- Fig. 6. Spectrogram (frequency [kHz]) and wave- form (rel. amplitude [kUnit] = proportional to form (rel. amplitude [kUnit] = proportional to sound pressure of the recording) of the advertise- sound pressure of the recording) of the advertise- ment call and non-collected specimen of Polype- ment call and non-collected specimen of Poly- dates leucomystax. Temperature during recording pedates otilophus. Temperature during recording 25.0 "C. 25.4 'C .

Fig. 5. Spectrogram (frequency [kHz]) and wave- Fig. 7. Spectrogram (frequency [kHz]) and wave- form (rel. amplitude [kunit] = proportional to form (rel. amplitude [kUnit] = proportional to sound pressure of the recording) of the advertise- sound pressure of the recording) of the adver- ment call and non-collected specimen of Poly- tisement call and non-collected specimeil of Bufo pedates macrotis. Temperature during recording asper. Temperature during recording 24.6 "C. 24.9 "C.

calculated regression except Bufo asper and Microkyla sp. All frog species in the road- side habitat are below the calculated regres- sion. The largest frog species was Polypedates otilopkus with a dominant call frequency of 1,033.6 Hz. No frog species with a dominant call frequency below 1,000 Hz was recorded. Frequencies of advertisement calls of anuran species found in the stream transect are high- er than call frequencies recorded of species occurring in the roadside habitat (Fig. 14) (N

= 11; df = I; F = 7.315, P = 0.024). Dominant frequency is not dependent on the SVL (N = 11; df = 1; F = 3.822, p = 0.082) but the influ- ence of the habitat is significant (N = 11; df = I; F = 7.031, P = 0.029). If the number of ana- lyzed individuals is included, the dependen- cy of the dominant frequency, the influence 0f SVL (N = 11; df = 1; F = 0.519, p = 0.049) and the influence of the habitat (N = 11; df =

1; F = 11.435, p = o.010) become more signifi- cant.

Aiiuran acoustic communities in Sabah, Malaysia

Fig. 8. Spectrogram (frequency [ ~ H Z ] ) and wave- Fig. 10. Spectrogram (frequency [ ~ H Z ] ) and wave- form (rel. amplitude [kUnit] = proportional to form (rel. amplitude [kunit] = proportional to sound pressure of the recording) of the advertise- sound pressure of the recording) of the advertise- inent call aild non-collected speciinen of Meristog- ment call and non-collected specimen of Staurois enys orphnocnemis. Temperature during recording natator. Ternperature during recording 25.3 "C. 24.8 "C.

Fig. 9. Spectrogram (frequency [kHz]) and wave- form (rel. amplitude [kUnit] = proportional to sound pressure of the recording) of the advertise- ment call and non-collected speciinen of Micro- hyla sp. Temperature during recording 25.3 "C.

Discussion

The comparison of two local frog assem- blages in different habitats shows that adver- tisement calls of frog species living in noisy environments constrain higher frequencies. Fast flowing streams and waterfalls produce low-frequency-dominated noise which may present a selective force for stream-breeding species (HÖDL 8r AMEZQUITA 2001, FENG et al. 2006). The high-frequency calls exceed the constant ambient noise level. Spectro-

Fig. 11. Spectrogram (frequency [kHz]) and wave- form (rel. amplitude [kUnit] = proportional to sound pressure of the recording) of the advertise- ment call and non-collected specimen of Staurois latopalmatus. Temperature during recording 25.2 0,-

grams of streams show high sound pressure levels in low frequencies and lower sound pressure levels in frequencies above 3,000 Hz (HÖDL & AMEZQUITA 2001, FENG et al. 2006, authors' unpublished data). Environ- mental constraints should have an effect on the evolution of signals (NARINS 8r ZELICK 1988). Selection favors signals that minimize the effects of background noise and inter- fering signals from other species (ENDLER 1993). Riparian frog species are acoustically well adapted to their environment and show

DORIS PREININGER et al.

Fig. 12. a) I„ . varya nicobariensis, b) Fejervarya limnocharis, C) Rhacophorus dulitensis, d) Polypedates leucomystax, e) Polypedates macrotis, f) Polypedates otilophus, g) Bufo asper, h) Meristogenys orphnoc- nemis, i) Microhyla sp., j) Staurois natator, k ) Staurois latopalmatus. Photos: M . BÖCKLE, W. HÖDL, T. REIS.

Anuran acoustic communities in Sabah, Malaysia

strong habitat affiliations. With the exception of Bufo asper the mean dominant frequency was above 3.9 kHz for frogs calling in the un- disturbed habitat. A possible explanation for the call frequency in B. asper could be that it prefers stream banks, with small riffles that produced less background noise. Addition- ally, dominant frequency is determined by SVL. Larger frogs call with lower frequencies than smaller frogs (LITTLEJOHN 1977, KIME et al. 2000). The sampling size was proba- bly too small to produce the dependency of SVL on dominant frequency. Only weighted data were able to show the influence. All spe-

cies found in the disturbed roadside habitat call with lower frequencies and less constant noise is emitted by the surrounding environ- ment. This gives rise to the question why a high proportion of species breeds close to fast flowing streams (INGER 1969). ZIMMER- MAN & SIMBERLOFF (1996) showed that re- productive mode and developmental habitat are strongly associated with phylogeny. The Same limited Set of ecological and reproduc- tive traits is shared by ranids, pelobatids and rhacophorids. Environmental conditions and interspecific interactions may have led to ad- aptations, but local selection on species can not be counted independent when closely re- lated species occur in the Same community. Phylogeny was not included in our analysis and a certain bias may result from the fact that two species of the genus Staurois are present at the stream habitat. Advertisement calls are important determinants of repro- ductive success and could have evolved in a common ancestor. However, we were able to record five species of the farnily of ranids, three at the stream (Staurois latopalmatus, S. natator and Meristogenys orphnocnemis) and two along the roadside (Fejervarya nico- bariensis and E limnocharis). All three ranid species recorded along the stream produce advertisement calls in which the dominant frequencies are above the calculated linear regression line (Fig. 13). Although morpho- logical and phylogenetic limitations con- strain frog vocalizations, selective pressures

+ such as environmental factors have resulted in a diversity of advertisement calls (DUELL- MAN & TRUEB 1986). Acoustic partitioning and increasing the signal-to-noise ratio are prerequisites for frogs living along torrents and streams. The influence of the habitat on advertisement calls should emphasize the importance of microhabitat composition on frog assemblages. Most recorded species are threatened by habitat loss (Tab. 1). Deforesta- tion and subsequent siltation of streams and rivers are the major threats to most stream- breeding species in Sabah. Out of twelve spe- cies found along the stream, three are clas-

DORIS PREININGER et al.

~Meristogenys oiphnocnemis

@

0 Fejervatya limnocharis

Bujo asper

SVL [mm]

Fig. 13. Influence of SVL on dominant frequency of the species advertisement call (y = -55.49~ + 5,472.71). Frog species of the stream transect are marked with a Square, those from the roadside habitat with a circle.

Roadside Stream

Fig. 14. Dominant call frequencies of the anuran species from two different habitat types. Species along the stream call with higher frequencies than frog species in the roadside habitat.

sified as "near threatened according to the IUCN Red List Status (Tab. I). INGER & VORIS (1993) found that a stream with a silt bottom

completely lacked all the species known to breed along clear and fast flowing streams. Selective logging changes the water chemis- try considerably in nearby streams. Sediment yields of streams are 18 times higher within the next five months in selectively logged ar- eas (DOUGLAS et al. 1992,1993). The increase in sedimentation levels has a clear effect on larval anurans and on reproduction of sever- al stream-breeding species. Frog assemblages as those found at the Tembaling River show the importance of conservation areas like Danum Valley. On the other hand more mi- crohabitats are created through reduced im- pact logging which attracts frog species that are normally not found in primary forests (e.g., Polypedates macrotis, Fejervarya nico- bariensis and Rhacophorus pardalis) (WONG in press). We believe that disturbed areas such as those around the Danum Valley Field Center and adjacent roads contain suitable ponds and breeding habitats for disturbance- tolerant breeders, but the large destruction

Anuran acoustic communities in Sabah, Malaysia

Tab. 1. List of anuran species found including weight, snout-vent length (SVL), dominant call frequency (DF) and IUCN Red List status. Habitat: 1 = stream, 2 = road edge (numbers in parentheses are the ab- solute number of individuals measured); weight [g]; SVL [mm]; dominant frequency, DF [Hz] (number of individuals/number of analyzed calls); major threat: HL = habitat loss, P = pollution of streams and rivers, ID = infrastructure development, N = none; Red List status according to IUCN et al. (2006).

species habitat SVL DF major threat IUCN Red List status

Bufo asper 1 76.2 (1) 1,031.2 (119) HLIP least concern Meristogenys orphnocnemis 1 30.2 (4) 7,205.0 (116) HLIP least concern Microhyla sp. 1 14.9 (5) 3,969.3 (4125) Staurois natator 1 33.9 (4) 4,746.0 (3119) HLIID least concern Staurois latopalmatus 1 47.7 (11) 5,149.4 (5120) HLIP least concern Ansonia longidigita 1 HLIP near threatened Ansonia spinulifer 1 3.2 (1) HLIP near threatened Leptobrachium abbotti 1 56.5 (5) HL least concern Limnonectes leporinus 1 106.8 (1) HL least concern Rana picturata 1 39.8 (2) HL least concern Pedostibes rugosus 1 HLIP near threatened Chaperina fusca 1 18.8 (1) HL least concern Chaperina fusca 2 HL least concern Polypedates leucomystax 2 30.0 (7) 2,056.7 (4135) N least concern Polypedates inacrotis 2 57.0 (5) 1,388.9 (113) N least concern Polypedates otilophus 2 81.1 (9) 1,033.6 (112) HL least concern Fejervarya limnocharis 2 33.4 (3) 1,274.0 (313) least concern Fejervarya nicobariensis 2 41.2 (6) 3,169.7 (5144) HLIN least concern Rhacophorus dulitensis 2 46.6 (4) 1,868.6 (5147) HL near threatened Rhacophorus pardalis 2 43.5 (6) HL least concern Occidozyga laevis 2 31.0 (10) N least concern

and fragmentation of primary forest poses a major threat to the characteristic herpetofau- na of Sabah.

Acknowledgements

We thank the Danum Valley Management Com- mittee, the Economic Planing Unit, the Sabah Wildlife Department and the Universiti of Ma- laysia Sabah for giving us the opportunity to work in the Danum Valley Conservation Area. Special thanks go to the Royal Society (RS) and GLEN REYNOLDS for their support and commitment to make this project possible. JULIA FELLING and KAROLINE SCHMIDT assisted during our fieldwork and MARKUS GMEINER did the photo editing. We are very thankful for the statistical help of ADOLFO AMEZQUITA. ANNA WONG acted as our local col- laborator. Financial support was given by the Uni- versity of Vienna (Brief Scientific Stays Abroad) and the DGHT (WILHELM-PETERS-Fonds). The Department of Evolutionary Biology (University of Vienna) provided the necessary field equip- ment. Last but not least we thank the DVCA and RS staff for keeping our Spirits up.

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Manuscript received: 24 August 2006

Authors' addresses: DORIS PREININGER, MARKUS BÖCKLE, WALTER HÖDL, Department for Evolu- tionary Biology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria, E-Mails: doris- preininger@hotmail.com; markus.boeckle@gmail.com; walter.hoedl@univie.ac.at.