Evaluation of the Effectiveness of Three Survey Methods for Sampling Terrestrial Herpetofauna in South China
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Herpetological Conservation and Biology 6(3):479–489. Submitted: 9 July 2011, Accepted: 16 October 2011 Published: 31 December 2011. EVALUATION OF THE EFFECTIVENESS OF THREE SURVEY METHODS FOR SAMPLING TERRESTRIAL HERPETOFAUNA IN SOUTH CHINA 1 YIK-HEI SUNG, NANCY E. KARRAKER, AND BILLY C.H. HAU School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, China 1Corresponding author, email: [email protected] Abstract.—Southeast Asia exhibits high herpetofaunal biodiversity, yet many areas and taxa in the region remain understudied. Extensive surveys are needed to fill information gaps, yet at present we have little knowledge about the effectiveness of different herpetofaunal survey methods in the region. We conducted field studies to examine the effectiveness of three survey methods for sampling terrestrial amphibians and reptiles in Hong Kong. Transect surveys were the most effective at sampling species richness and drift fences with pitfall traps and funnel traps were the most efficient in capturing high numbers of reptiles. We recommend the use of transect surveys for rapid biodiversity assessment and the combination of transect surveys and pitfall traps for comprehensive species inventories. Pitfall traps represent an excellent tool for surveys or population monitoring of leaf litter species. The results of this study will aid researchers in assessing the feasibility of and in choosing herpetofaunal survey methods in Southeast Asia. Key Words.—amphibians; coverboards; drift fences; monitoring; pitfall traps; reptiles; species inventories; transect surveys INTRODUCTION applied (Gardner et al. 2008). Therefore, successful studies must employ survey methods that permit the Many amphibian and reptile populations are declining most efficient completion of study objectives (Ribeiro- at unprecedented rates and some risk extinction under Junior et al. 2008). However, there are numerous factors the threats of global climate change, habitat loss, human influencing the effectiveness of different survey methods, exploitation, invasive species, pollution, and diseases including geographical area, habitats being sampled, (Gibbons et al. 2000; Stuart et al. 2004). Yet, target taxa, and duration and aim of the study (Greenberg amphibians and reptiles are among the most et al. 1994; Doan 2003). For herpetofaunal studies, understudied vertebrate taxa in Southeast Asia and the researchers have long debated the choice of survey population status of most species is unknown (Rowley et methods based on all of the above-mentioned factors. al. 2010). There is an urgent need to collect baseline There is a general consensus that no single survey data on population status and to initiate monitoring method can sample all species of amphibians and programs for amphibian and reptile species in the region reptiles in a community (Ryan et al. 2002), but to detect any responses to threats and environmental depending upon the variety of factors influencing changes (Gibbons et al. 2000). effectiveness and overall goals of the study, some Southeast Asia, including Indo-Burma, the Philippines, approaches may procure more precise estimates of and Sundaland have been identified as biodiversity abundance or diversity than others. hotspots (Myers et al. 2000; Bickford et al. 2010) and A number of herpetofauna sampling methods are high biodiversity in this region includes herpetofauna available for answering ecological questions or (Bickford et al. 2010; Rowley et al. 2010). New species conducting inventories (Doan 2003; Dodd 2009). The of herpetofauna are frequently discovered and described most commonly used methods include coverboards, drift (Chou et al. 2007; Grismer and Ngo 2007; Wang et al. fences with pitfall traps (hereafter pitfall traps), and 2010), suggesting that herpetofauna in this region transect surveys (Doan 2003; Willson and Gibbons remains understudied. More effort should be expended 2009). The effectiveness of these survey methods for in Southeast Asia conducting herpetofaunal surveys to sampling abundance, species richness, and species produce inventories and discover cryptic and composition of herpetofauna varies among studies. undescribed taxa (Bickford et al. 2010). Some researchers have suggested that pitfall traps and Ecological studies, including population monitoring coverboards sample herpetofauna in a more standardized and biodiversity inventory surveys, are often limited by way than transect surveys and these methods are capable resource availability and the amount of effort that can be of capturing rare and secretive species that are harder to Copyright © 2011. Yik-Hei Sung. All Rights Reserved. 479 Herpetological Conservation and Biology detect (Ribeiro-Junior et al. 2008; Willson and Gibbons (Machilus spp.) and Red Psychotria (Psychotria 2009). Capture rates have been demonstrated to be quite asiatica). The exotic plantation and native forest were high with these two methods in some areas (Ryan et al. greater than four hectares in size at each site. All study 2002; Hampton 2007; Ribeiro-Junior et al. 2008). The sites were below 400 m above sea level. use of coverboards is common, particularly in North America, as they can be easily deployed, allow samples Herpetofauna sampling.—Twenty-three species of to be obtained in a relatively shorter time than transect amphibians and 70 non-marine, native reptiles occur in surveys, and require almost no maintenance (Grant et al. Hong Kong (Karsen et al. 1998). Of these, 10 species of 1992; Hampton 2007). For pitfall traps, one of the main amphibians and 30 species of reptiles are forest-dwelling disadvantages is that their use is costly in terms of the and potentially occur within the study areas. We tested time and labor required to set up and maintain arrays three herpetofaunal survey methods, including (Todd et al. 2007). Transect surveys are preferred by coverboards, pitfall traps, and transect surveys. some researchers as they have been demonstrated to be We conducted all sampling methods at least 30 m effective at sampling both abundance and species from the edge of the forest and from any perennial richness in some regions, such as Africa (Doan 2003; streams so as to avoid edge effects and to focus on Rodel and Ernst 2004). sampling terrestrial herpetofauna. We distributed 0.66 m Studies comparing herpetofaunal survey methods have x 0.66 m x 0.018 m coverboards made of plywood at been conducted in a number of regions including North each site to provide shelters for herpetofauna. Within America (Crosswhite et al. 1999; Ryan et al. 2002; each forest type at each site, we placed a set of 10 Hampton 2007; Todd et al. 2007), South America (Doan coverboards at 10 m intervals along each transect for two 2003; Ribeiro-Junior et al. 2008), Africa (Rodel and transects (i.e., a total of 20 coverboards in each forest Ernst 2004), and Australia (Garden et al. 2007). Yet, type). We randomly selected the starting points of each there have been very few studies comparing the coverboard transect and ensured that coverboard effectiveness of herpetofaunal survey methods transects and pitfall trap arrays were located at least 30 quantitatively in Southeast Asia (but see Gillespie et al. m apart within the same forest type. We checked 2005; Hsu et al. 2005). Thus, our goal was to address coverboards during the day twice a month from August this question in South China, specifically focusing on 2008 (sites Lung Fu Shan and Tai Lam) and September terrestrial species, which, given the high diversity of 2008 (sites Tai Po Kau and Shing Mun) to September reptiles, make up a large part of the herpetofauna in the 2009. region. Our specific objective was to determine the We established a pitfall trap transect within each effectiveness of three commonly used herpetofaunal exotic plantation and secondary forest (Gibbons and survey methods, including coverboards, pitfall traps, and Semlitsch 1982). Five trap arrays were installed along transect surveys, by evaluating capture rates, observed each transect, with each array consisting of three 18.9 L species richness, and sampled species composition in buckets, two double-ended funnel traps, and a 10 m of South China. This study aimed to provide guidance for drift fence. We positioned each trap array 10 m apart herpetologists on the choice of survey methods for future along a transect. We constructed drift fences by stapling studies in the region. 0.4 m tall, transparent plastic sheeting to wooden stakes and by burying the bottom 0.1 m of the plastic sheeting MATERIALS AND METHODS to prevent animals from crossing underneath. We buried three pitfall traps along each fence: one at each end and Study sites.—We conducted this study from March one in the middle so that the openings of buckets were 2008 to August 2010 within the Hong Kong Special flush with the ground level. We used lids of buckets to Administrative Region (lat. 22°09’ – 22°37’N; long. cover the traps when they were not in use. To prevent 113°50’ – 114°30’E). While parts of Hong Kong are drowning of animals, we drilled five 12.5 mm diameter highly urbanized, approximately 40% of the 1,100 km2 holes in the bottom of each bucket for drainage. land area is protected as national parks. We selected four Preliminary sampling indicated that shrews caught in parks as our study sites: Tai Po Kau Special Area pitfall traps caused mortality of skinks, so we stapled a (hereafter Tai Po Kau), Lung Fu Shan Country Park string on the edge of the buckets to allow small (hereafter Lung Fu Shan), Shing Mun Country Park mammals to escape (Karraker 2001). We found no small (hereafter Shing Mun), and Tai Lam Country Park mammal in buckets equipped with escape string (hereafter Tai Lam). Each site included a plantation of throughout the study period. We made funnel traps from the exotic Brush Box (Lophostemon confertus), a tree 0.3 m x 0.4 m of aluminum window screen, which we introduced from Australia that is the most widely planted rolled into a cylinder and stapled. We inserted wire tree species in Hong Kong (Dudgeon and Corlett 2004), mesh funnels with the openings of approximately 0.04 m and a native secondary forest.