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

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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.
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
Rheinbach, 20 August 2007 ISSN 0036-3375129-138
3
43
SALAMANDRA
http://www.salamandra-journal.com

Comparison of anuran acoustic communities of two
habitat types in the Danum Valley Conservation Area,
Sabah, Malaysia

Abstract. (i)
(ii)



  
    


Introduction

     

   

    
       
  
      
      

 
  


      

 
       
   
    
   
    

      

  

     
    
     




     






     
      


     
      
 
       
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
      


Material and methods



      


   





    
  
     


      
    


     

      
   
     
      

      







     




      
  

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    
 
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  
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      
 


     
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  
    
    
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    
 
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

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      
       
      
    
    
     
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      

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

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


 



    

Results
  


Fejervarya nicobarien-
sis   Fejervarya limnocharis  
Rhacophorus dulitensis   Polypedates
leucomystax   Polypedates macrotis
  Polypedates otilophus   
Bufo asper   Meristogenys orphnocne-
mis   Microhyla    Staurois
natator Staurois latopalmatus
   



  
    
Meristogenys orphnocnemis

     
  

      

      Fejer-
varya nicobariensis   


      

 Fejervarya limnocharis


      

Rhacoph-
orus dulitensis

132

   Bufo asper 
Microhyla      
 
Polypedates
otilophus   
 



      


      

     Polype-
dates leucomystax


      

      Poly-
pedates macrotis   


      

      Poly-
pedates otilophus.   








   




      
       
Bufo
asper.
133

Discussion
      

 
   
 
   

  
     
     
 
      
     
       
    
   
      

      
     
     


      

Meristog-
enys orphnocnemis.


      

      Micro-
hyla 

      

Staurois
natator. 

      

Staurois
latopalmatus 

134

a b
cd
ef
gh
 Fejervarya nicobariensis,  Fejervarya limnocharis,  Rhacophorus dulitensisPolypedates
leucomystax,  Polypedates macrotis  Polypedates otilophus,  Bufo asper,  Meristogenys orphnoc-
nemis,  Microhyla Staurois natator,  Staurois latopalmatus. 

135


Bufo asper  


B. asper
      
    
     

    
       
 



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

       
      

     

   




    

   
   
        
      Staurois 

     
   
      

    Staurois latopalmatus,
S. natator  Meristogenys orphnocnemis
Fejervarya nico-
bariensisF. limnocharis
     
     
     
    
    
    


     
   
     

    

 


  
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      
      
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

      
                


 
      
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
      


  


   



     



      
 Polypedates macrotis, Fejervarya nico-
bariensisRhacophorus pardalis
      

     

     
 
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
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Acknowledgements

      
      

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        
  
     


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

      
    
    
      


     

Bufo asper    
Meristogenys orphnocnemis    
Microhyla    
Staurois natator    
Staurois latopalmatus    
Ansonia longidigita    
Ansonia spinulifer    
Leptobrachium abbotti    
Limnonectes leporinus    
Rana picturata    
Pedostibes rugosus    
Chaperina fusca    
Chaperina fusca    
Polypedates leucomystax   
Polypedates macrotis   
Polypedates otilophus    
Fejervarya limnocharis   
Fejervarya nicobariensis    
Rhacophorus dulitensis    
Rhacophorus pardalis    
Occidozyga laevis   





References
      
     
     
3
 
  

    
303
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      
     
  3

        

 

  
235

  
138

     65
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  
983
       

 

 
340


 
440:
     

57:
      


      

     

20
 
     
    
28
       
       
     

     
  
38
       
   
        
9
    
 
  

       
     


     
      
  
     

     

. ,335

   
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 

       
 
 
     
      
      

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... They communicate in their own niche to get their individual messages across (Pijanowski et al., 2011). In particular, anurans use temporal and call spectral features to minimize competition for better recognition of individuals (Preininger et al., 2007). Anuran call characteristics, such as diversity of notes, number of pulses per note, or dominant frequency, are strongly associated with taxonomy. ...
... In the Danum Valley Conservation Area (DVCA), the acoustic partitioning of different frog species was examined in two microhabitat and disturbance gradients: selectively logged forest along a road and in a forest trail to Tembaling waterfalls. Dominant frequency was found to be linked to snout-vent length (SVL) except for species in noisy environments of fast flowing streams near the waterfalls (Preininger et al., 2007). For the present study, the soundscapes of breeding congregations (pools) and inside forest trails were compared. ...
... Calls can further be influenced by environment variation (Wei Li et al. 2011), such as different ambient noise that influence the dominant frequency and SPL. Frog advertisement calls in noisy environment contain higher frequencies (Preininger et al. 2007). The comparison between the different soundscapes showed a frog chorus that is unique to each specific soundscape. ...
Research
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This is to certify that Arfah Nasution and Nikki Dyanne Realubit successfully completed a field course in tropical ecology and conservation. The month long course covered current concepts and techniques in ecology, conservation biology, experimental design and sampling methods. This was delivered through a series of lectures, seminars, practical analysis and an independent two week research project held at DANUM VALLEY CONSERVATION AREA, SABAH, MALAYSIA. Abstract Acoustic signaling plays an important role in anuran reproduction, and the structure of advertisement calls is strongly linked to taxonomy. To reveal whether microhabitat and environment factors further determine variation in dominant frequencies across different species, we compared frog calls of nine species recorded from different sites characterized by diverging soundscapes (three pools and forest trails). Sound pressure level (SPL) was measured alongside calls to gauge the ambient noise levels. Dominant frequencies (DF) differed across species which varied in SPL. Moreover, DF and SPL were found to be significantly different across sites. Frogs were calling at higher frequencies in the three pools, with generally lower frequencies found along forest trails. We suggest that forest frogs are more dispersed, leading to less competition between species, whereas higher competition in a pool environment leads to louder calls at overall higher frequencies. For two species (Rhacophorus appendiculatus and Hylarana nicobariensis), sufficient data were available to investigate the relationship between DF and snout-vent length (SVL). Unexpectedly, larger H. nicobariensis tended to call at lower frequencies, whereas larger R. appendiculatus called at lower frequencies, however without significant correlation between DF and SVL. Species habitat preference and low sample size may explain these observations.
... Despite evidence that supports the effect geophonies have on the sonic behavior of marine (Brumm and Zollinger, 2011;Holt and Johnston, 2014;Guazzo et al., 2020;Helble et al., 2020) and terrestrial animal vocalizations (Brumm and Slater, 2006;Preininger et al., 2007;Brumm and Naguib, 2009;Samarra et al., 2009;Vargas-Salinas et al., 2014) and species evolution (Ryan and Brenowitz, 1985;Brumm and Slabbekoorn, 2005), there still exists a gap in our understanding the natural selection process of geophony in animal evolution, more specifically in terrestrial systems. Boeckle et al. (2009), for instance, found rockkipper frogs (Staurois latopalmatus) in habitats with continuous geophony from waterfalls emitted higher frequency calls and had smaller body sizes than cohorts where geophony was not as sonically pronounced. ...
Article
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Humans categorize unwanted sounds in the environment as noise. Consequently, noise is associated with negative human and ecological values, especially when it is derived from an anthropogenic source. Although evidence confirms that many machine-generated anthropogenic sounds have negative impacts on animal behavior and communication, natural sources of non-biological sound, such as wind, rain, running water, and sea waves (geophonies) have also been categorized as noise and are frequently dismissed or mischaracterized in acoustic studies as an outside factor of acoustic habitats rather than an integrated sonic component of ecological processes and species adaptations. While the proliferation of machine-generated sound in the Biosphere has become an intrusive phenomenon in recent history, geophony has shaped the Earth’s sonic landscapes for billions of years. Therefore, geophonies have very important sonic implications to the evolution and adaptation of soniferous species, forming essential ecological and semiotical relationships. This creates a need to distinguish geophonies from machine-generated sounds and how species respond to each accordingly, especially given their acoustic similarities in the frequency spectrum. Here, we introduce concepts and terminology that address these differences in the context of ecoacoustics. We also discuss how Acoustic Complexity Indices (ACIs) can offer new possibilities to quantifiably evaluate geophony in relation to their sonic contest.
... Bell, 2020), but diverse ecological factors are capable of promoting the present spatial segregation of the body size of species (Nevo, 1973;Duellman & Thomas, 1996;Morrison & Hero, 2003;Wells, 2007;Campos et al., 2017), and one of these factors is the level of abiotic noise in the habitat (Goosem et al., 2007;Röhr et al., 2016). In fact, anuran assemblages alongside streams tend to exhibit lower average values and less variability in male body size than anuran assemblages located away from streams (Preininger et al., 2007;Boeckle et al., 2009;Carvajal-Castro & Vargas-Salinas, 2016). Based on this, in addition to the relationship between body size and functional traits, FD is expected to be lower in anuran assemblages alongside streams than in anuran assemblages away from streams (Fig. 2), as a concomitant effect of a habitat filtering process imposed by abiotic noise (Francis et al., 2009(Francis et al., , 2011(Francis et al., , 2012Carvajal-Castro & Vargas-Salinas, 2016). ...
Article
The abiotic noise of streams can mask the acoustic signals of anurans with a large body size calling at low frequencies, but not the signals emitted by anurans with a small body size calling at high frequencies. As a consequence, the body size of species in assemblages alongside streams is, on average, lower and less variable than that of assemblages away from streams. Given that the body size in anurans is frequently related to life-history traits, it is expected that functional diversity (FD) will be lower in anuran assemblages alongside streams than in assemblages away from streams. We calculated and compared FD, based on six functional traits, for anuran species in seven localities in different biogeographical regions in the Neotropics. In five lowland localities, FD was lower in assemblages alongside streams than in assemblages away from streams. However, the reverse trend was found in two Andean localities. Noise from streams, acting as an environmental filter, could promote low FD because taxa whose phenotype differs from an optimal type (high call frequency, small body size and associated traits) are excluded from riparian places. However, such habitat filtering could be stronger and affect more anurans in lowland assemblages than in those at medium elevation.
... They also found that individuals who breed near the river have a smaller body size than those who do not. However, Preininger et al. (2007) and Boeckle et al. (2009) found that anurans that breed in flowing water have a higher DF. We eliminated the impact of SVL and phylogenetic relationships, and the results showed that the DF of the 53 anuran species in China was significantly higher in flowing water than in stagnant water, which is similar to the findings of Röhr et al. (2016). ...
Article
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Vocalization plays an important role in the communication of anurans. In this study, the advertisement calls of male Fejervarya multistriata obtained in Lishui, Zhejiang, China during the breeding season were recorded. Their note number (NN), note duration (ND), note interval (NI), call duration (CD), pitch (PIT), call intensity (CIT) and dominant frequency (DF) were analyzed. The calls of F. multistriata are composed of one to 38 notes, and calls composed of fewer than ten notes have the highest frequency. Male frogs produced calls ranging from 1201 Hz to 3357 Hz with two DFs (1412.49 Hz and 2953.89 Hz). By comparing the differences among individual calls, it was found that the within-individual coefficients of variation (CV W ) and among-individual coefficients of variation (CV A ) for NN, NI, CD, PIT and DF were more than 10%, whereas that of CIT was less than 5%. The CV A /CV W ratios indicate that ND is important for sexual selection, whereas NN, NI CD, PIT, CIT, and DF are important for individual recognition. Phylogenetic generalized least squares analysis showed that phylogenetic signals affect DF vs. snout-vent length (SVL) and CD of anurans in China, and accounting for phylogenetic signals, DF was negatively correlated with SVL. DF was found to be higher in anurans that breed in flowing water than in those that breed in stagnant water, after eliminating the effects of phylogeny and SVL. Therefore, we conclude that phylogenetic effects, SVL, and the water type of breeding habitats have a combined impact on the advertisement calls in anurans.
... Some of this variation may be attributed mainly to sexual selection in a strict sense (Wilbur et al. 1978, Gerhardt 1991, Márquez 1995, Rosso et al. 2006, Röhr and Juncá 2013 and some to environmental limitations (e.g., Ryan et al. 1990;Ryan and Wilczynski 1991, Kime et al. 2000, Castellano et al. 2003, Röhr and Juncá 2013. For example, the transmission of a sound signal can be affected by its acoustic characteristics (Morton 1975, Marten et al. 1977, Ryan and Sullivan 1989, Kime et al. 2000 as well as by a variety of other factors such as habitat and vegetation structure (Wiley and Richards 1978, Sorjonen 1986, Ryan et al. 1990, Endler 1992, ambient noise (Feng et al. 2006, Preininger et al. 2007, climatic conditions (Wiley and Richards 1978), and height of vocalization perch (Wiley and Richards 1978, Wilczynski et al. 1989, Kime et al. 2000, Papes 2011). Furthermore, ambient temperature affects hearing in invertebrates and ectothermic vertebrates (Narins 2001, Papes 2011. ...
Article
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Bioacoustics is an interdisciplinary science that combines biology, acoustics, and mathematics. This discipline can be used to study population ecology and behavior. Furthermore, we can use this tool to assess a population and suggest if a species of interest may be in a transitional state of becoming a new species by allopatric speciation. Amphibians communicate via sound and the environment has a key role in metabolism and sound dispersion. By analyzing temporal and spectral properties of acoustical communication in anurans, we can understand better how these animals are evolving to cope with their ever-changing environment. We studied the variation in acoustic parameters among five populations each of the red-eye coqui, Eleutherodactylus antillensis (Reinhardt and Lutken, 1863) and the common coqui, E. coqui Thomas, 1966 across the Puerto Rico Bank. These species are changing their vocalizations. Some populations have higher sound frequencies than other conspecific populations; other nocturnal species have populations with different temporal patterns of sound production. We found strong variation among the five populations examined for each species. In, E. antillensis, the size of the organism relates to temporal variation in sound production (i.e., inter-note interval and total call duration) and did not relate to spectral differentiation. In E. coqui, the population living at highest elevation above sea level assessed had a spectral footprint no other population shares, probably due to geographic isolation from other conspecific populations that live in lower elevations.
... Geophonic activity is nearly ever-present and more variable than other acoustic phenomena (Farina and Gage 2017). Although many studies have shown that geophony can have a significant influence on animal vocalizations (Brumm and Slater 2006;Preininger et al. 2007;Brumm and Naguib 2009;Samarra et al. 2009;Vargas-Salinas et al. 2014) and their evolution (Ryan and Brenowitz 1985;Brumm and Slabbekoorn 2005), very little is known about how geophony influences species habitat selection. However, we suspect that geophony provides a form of information that an animal can use to identify resources (e.g., the flow of water in a stream), areas to avoid (e.g., high wind), or locations to feed (e.g., the cracking of shifting ice revealing open water). ...
Article
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Sound is an inherent component of the environment that provides conditions and information necessary for many animal activities. Soniferous species require specific acoustic and physical conditions suitable for their signals to be transmitted, received, and effectively interpreted to successfully identify and utilize resources in their environment and interact with conspecifics and other heterospecific organisms. We propose the Acoustic Habitat Hypothesis to explain how the acoustic environment influences habitat selection of sound-dependent species. We postulate that sound-dependent species select and occupy habitats with unique acoustic characteristics that are essential to their functional needs and conducive to the threshold of sound frequency they produce and detect. These acoustic habitats are based on the composition of biophony, geophony, and technophony in the soundscape and on the biosemiotics mechanisms described in the eco-field hypothesis. The Acoustic Habitat Hypothesis initiates questions of habitat selection that go beyond the physical attributes of the environment by applying ecoacoustics theory. We outline the theoretical basis of the Acoustic Habitat Hypothesis and provide examples from the literature to support its assumptions. The concept of acoustic habitats has been documented in the literature for many years but here, we accurately and extensively define acoustic habitat and we put this concept into a unified theory. We also include perspectives on how the Acoustic Habitat Hypothesis can stimulate a paradigm shift in conservation strategies for threatened and endangered species.
... Stuart et al. 2010). The high frequency parameters may be related with their tendency to vocalize in close proximity to mountain cascade streams, which would create a low-frequency background noise (Preininger et al. 2007). It was shown that low background noise may induce frogs to call at higher frequency rates than expected from their body size, thereby improving the signal-to-noise ratio of their calls (Penna et al. 2005, Wells 2007, Goutte et al. 2016). ...
Article
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Asian Mountain Toads (Ophryophryne) are a poorly known genus of mostly small-sized anurans from southeastern China and Indochina. To shed light on the systematics within this group, the most comprehensive mitochondrial DNA phylogeny for the genus to date is presented, and the taxonomy and biogeography of this group is discussed. Complimented with extensive morphological data (including associated statistical analyses), molecular data indicates that the Langbian Plateau, in the southern Annamite Mountains, Vietnam, is one of the diversity centres of this genus where three often sympatric species of Ophryophryne are found, O. gerti, O. synoria and an undescribed species. To help resolve outstanding taxonomic confusion evident in literature (reviewed herein), an expanded redescription of O. gerti is provided based on the examination of type material, and the distributions of both O. gerti and O. synoria are considerably revised based on new locality records. We provide the first descriptions of male mating calls for all three species, permitting a detailed bioacoustics comparison of the species. We describe the new species from highlands of the northern and eastern Langbian Plateau, and distinguish it from its congeners by a combination of morphological, molecular and acoustic characters. The new species represents one of the smallest known members of the genus Ophryophryne. At present, the new species is known from montane evergreen forest between 700–2200 m a.s.l. We suggest the species should be considered Data Deficient following IUCN’s Red List categories.
... A further constraint of acoustic resource partitioning is probably the limited frequency range available for an anuran advertisement call (e.g. Garcia-Rutledge & Narins 2001;Preininger et al . Fig. 4. Cluster analysis (method: complete linkage) of bioacoustic niche overlap of 14 species comprising the anuran community of the swamps near Butare. ...
Article
The species richness and calling activity of an anuran community inhabiting an agricultural wetland area at 1645 m a.s.l. near Butare, Rwanda, was assessed using visual and acoustic transects. The community included 15 species which were readily distinguishable using morphological, bioacoustic and molecular features. Eight species (Xenopus victorianus, Amietophrynus regularis, Ptychadena anchietae, P. porosissima, Kassina senegalensis, Afrixalus quadrivittatus, Hyperolius kivuensis, H. lateralis) were taxonomically identified. The remaining seven species (three species of Hyperolius, two Phrynobatrachus, one Amietia, one Ptychadena) represent undescribed or currently unrecognized taxa, suggesting a significant magnitude of overlooked amphibian diversity in Afromontane communities. Acoustic niche analysis of the 14 species producing airborne advertisement calls integrated the spatial dimension, i.e. the microhabitat used for calling, the temporal dimension, i.e. the time of day when calling takes place, and the call structure dimension, i.e. the physical features of the advertisement call. Average standardized acoustic niche breadth was narrow (measured: 0.08, predicted: 0.07) and showed low variability (0.04–0.16) among species, which means that empirical data are in full agreement with the predictions of stochastic niche theory for species-saturated communities. Niche segregation was mainly based on advertisement call features, whereas spatial and temporal niche dimension contributed less. Measured average niche overlap (0.30) was intermediate between random overlap (0.51) and minimum possible overlap (0.11), indicating significant acoustic resource partitioning. The only taxon group with widely overlapping acoustic niches were Ptychadena spp., which might indicate a recent invasion of the community by one or two of the three species.
Article
Aim The diversity of brood size across animal species exceeds the diversity of most other life‐history traits. In some environments, reproductive success increases with brood size, whereas in others it increases with smaller broods. The dominant hypothesis explaining such diversity predicts that selection on brood size varies along climatic gradients, creating latitudinal fecundity patterns. Another hypothesis predicts that diversity in fecundity arises among species adapted to different microhabitats within assemblages. A more recent hypothesis concerned with the consequences of these evolutionary processes in the era of anthropogenic environmental change predicts that low‐fecundity species might fail to recover from demographic collapses caused by rapid environmental alterations, making them more susceptible to extinctions. These hypotheses have been addressed predominantly in endotherms and only rarely in other taxa. Here, we address all three hypotheses in amphibians globally. Location Global. Time period Present. Major taxa studied Class Amphibia. Methods Using a dataset spanning 2,045 species from all three amphibian orders, we adopt multiple phylogenetic approaches to investigate the association between brood size and climatic, ecological and phenotypic predictors, and according to species conservation status. Results Brood size increases with latitude. This tendency is much stronger in frogs, where temperature seasonality is the dominant driver, whereas salamander fecundity increases towards regions with more constant rainfall. These relationships vary across continents but confirm seasonality as the key driver of fecundity. Ecologically, nesting sites predict brood size in frogs, but not in salamanders. Finally, we show that extinction risk increases consistently with decreasing fecundity across amphibians, whereas body size is a “by‐product” correlate of extinction, given its relationship with fecundity. Main conclusions Climatic seasonality and microhabitats are primary drivers of fecundity evolution. Our finding that low fecundity increases extinction risk reinforces the need to refocus extinction hypotheses based on a suggested role for body size.
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Temporal and spectral characteristics of vocalizations of a multispecies frog assemblage in the Queen Sirikit Botanic Garden near Chiang Mai, Thailand were examined during the beginning of the breeding season in May 1997. Calls of eight frog species were recorded to determine the extent of temporal, spectral, and spatial separation observed among heterospecifics. Results show that some of the frogs sampled displayed clear temporal separation from the group (e.g., Rana pileata), others exhibited spectral separation (e.g., Chirixalus doriae), and still others were spatially separated from or on the edge of the group (e.g., Microhyla butleri). In addition, all species studied exhibited site fidelity on successive nights over the sampling period. Our observations suggest that frogs in this Old World disturbed community produce a variety of calling patterns that often results in reduction of mutual acoustic interference.
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The acoustic variation of each of three neotropical hylid frog communities was described on the basis of seven parameters of their advertisement calls. Comparisons between and among the three disjunct communities showed: 1) Patterns of total acoustic variation are alike among the three communities; 2) Calls of closely related allopatric species tend to be more similar than those of closely related sympatric species; and 3) Closely related sympatric species having similar calls are not syntopic and/or synchronous breeders. Therefore, it is suggested that each acoustic environment is partitioned distinctly by the particular anuran assemblage, but variation in acoustic partitioning is similar in disjunct communities of like habitat with different species composition.
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Three stages of selective commercial logging in a 0.54 km2 catchment in the Ulu Segama caused great changes in the output of sediment and water over a 27-month period from June 1988. The ratio of monthly suspended sediment yield from the logged catchment to that from a nearby undisturbed catchment changed from the order of 1:1 before disturbance; to 4:1 after a logging road had been built across the head of the catchment; to 5:1 after logging within 37 m of the road; and to 18:1 in the five months after logging of the remainder of the catchment. A year after logging had ceased the largest monthly sediment yields of the whole period were only 3.6 times those of the undisturbed catchment, indicating a degree of recovery. Sediment accumulated in the channel bed and on the narrow flood plain remained to be evacuated, and gullies on abandoned logging trails continued to supply sediment to the Drainage system.
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1. Along streams draining hilly rain forest in Sarawak and having widths of 10-70 ft (3-21 m), we find an assemblage of roughly twenty-five species of frogs either restricted to the riparian habitat for all postmetamorphic functions or tied to streams for breeding activities. 2. Nine species dominate the communities in the four streams having widths in excess of 20 ft (6 m). These nine species may be grouped into four main ecological types: large, strictly terrestrial, weakly clustered, riparian species; small to large, partially arboreal, weakly clustered, riparian species; small, partially arboreal, strongly clustered, riparian species; and one large, mainly arboreal, strongly clustered species that is not restricted to stream banks. 3. Phylogenetically related species tend to be associated in the same ecological types which leads to the conclusion that historical factors have been more important than contemporary ecological forces in the niche distribution of these species. 4. Equitability values based on the collections of the six study streams show little variation, which suggests similarity in community organization. Closer inspection of the relative abundances of ecological types on the several streams reveals a basic difference between the two smaller streams and the other four. Equitability values, therefore, provide a refined measure of similarity in community structure in detail only if examination of ecological types and their relative proportions indicates rough similarity at a coarse scale.
The international political economy of tropical rainforests related to their perceived role in global climatic change has to be set against real national and local political economies. These political economies involve socially driven biophysical responses with economic and social costs whose magnitude and distribution need to be known if policy formulation for improvement of living conditions is to succeed. Spatial linkages between changes and social costs, such as the downstream impacts of logging, need to be established, but before that can be done it is necessary to distinguish the effects of natural processes from those induced by people. In Malaysia logging or ground clearance increases river sediment yields by two to fifty times. Individual estimates may be unreliable indicators of the overall effects of change. However, the modifications to rivers as a result of raised sediment loads are increasing year by year. Site-based studies of the effects of both logging and shifting cultivation help to improve the data base for policy making and also indicate the efficiency of reduced impact logging and agroforestry techniques.
Article
The Malaysian state of Sabah occupies an area of 73 371 km2 which is about 10% of the island of Borneo. About 60% of the land area is forested and 48% is gazetted as Permanent Forest Reserve or State or National Parks. The largest agent of forest disturbance is the timber industry, which plays a leading role in the state economy. A statutory body, the Sabah Foundation, holds a 100-year timber concession of 973 000 ha (9730 km2) in the southeast of the state. Of this concession 9.7% has been reserved for conservation, including 43 800 ha (438 km2) of uninhabited, mostly lowland forest in an area called Danum Valley. Since 1986, this has been the site of a field centre and a collaborative research programme devoted to comparative study of primary forest ecology and the impacts of selective logging. The paper includes a summary account of the ecology of the Danum Valley Conservation Area.