Arachnologische Mitteilungen 58

Arachnologische Mitteilungen / Arachnology Letters 58: 23-28 Karlsruhe, September 2019 Comparing pitfall trapping and suction sampling data collection for ground-dwelling spiders in artificial forest gaps László Bali, Dániel Andrési, Katalin Tuba & Csaba Szinetár doi: 10.30963/aramit5808 Abstract. This study focuses on the comparison of two frequent ground-dwelling spider collecting methods, pitfall trapping and D-Vac suction sampling, in relation to artificial gap openings of a forest stand in West-Hungary. With pitfall traps, we collected 928 specimens, representing 34 species. With suction sampling, we collected 1254 specimens, belonging to 41 species. Examining the distribution of the communities, both sampling methods showed higher spider densities in forest gaps than in the forest stand. On average, the pitfall trapping accessed larger-sized spider species. The hunting and nocturnal spiders were also represented in the pitfall samples, while the D-Vac method detected more web builders. The ordination analysis showed that the two methods accessed different communities. Thus, we suggest their combined use. Keywords: Araneae, Carpathian Basin, D-Vac, gap, pitfall trapping, turkey oak Zusammenfassung. Vergleich von Bodenfallen und Saugfängen bodenlebender Spinnen auf künstlichen Waldlichtungen. Es werden zwei häufig angewendete Sammelmethoden verglichen, Bodenfallen und D-Vac Saugfänge, und zwar auf künstlichen Lichtun- gen in einem Waldbestand in Westungarn. Mit Bodenfallen wurden 928 Individualen aus 34 Arten gefangen. Mithilfe der Saugfänge wurden 1254 Individuen aus 41 Arten gesammelt. Bei beiden Methoden sind die Individuenzhalen auf den Lichtungen größer als im Wald. Mit Bodenfallen wurden im Durchschnitt größere Spinnenarten gefangen. Laufjäger nachtaktive Arten waren in den Bodenfallen stärker vertreten, während mit dem Saugfängen mehr netzbauende Arten gefangen wurden. Eine Ordination zeigt, dass beide Metho- den unterschiedliche Gemeinschaften erfassten. Daher schlagen wir ihre kombinierte Anwendung vor. Formation of gaps is a part of the natural regeneration process in temperate forests (Brokaw & Busing 2000, Vepakomma et al. 2008, Fledmann et al 2018, Senécal et al. 2018, Keram et al. 2019). In response to this, the popularity of ‘gap-cutting’ techniques is rising, and they may become essential in modern, close-to-natural forest management practices.The employment of these techniques is still relatively new however, therefore our information and understanding regarding their mechanics is lacking (Elek et al. 2018, Keram et al. 2019). In order to assess the effects of artificial gap openings on forest ecosystems and on forest floor arthropods, ground-dwelling spiders are suitable study objects (Wise 1993, Horváth et al. 2009, Elek et al. 2016, 2018). Two of the most commonly used methods for studying this taxon are pitfall trapping and suction sampling (Samu & Sárospataki 1995, Mommertz et al. 1996, Samu et al. 1997, Woodcock 2005, Kádár & Samu 2006). Because of their relatively cheap maintenance and low la- bour requirements, pitfall traps have been used to collect epi- geic arthropods since the early 1900s in many habitat types (e.g., Lang 2000, Zhao et al. 2013, McCravy 2018), including forests and forest gaps. Pitfall trapping is a passive sampling technique, as is suction sampling, in that they do not use any attractant (e.g., Zou et al. 2012, McCravy 2018).This method is considered to provide data on the degree of activity rather than actual population densities of the captured species, and tend to over-represent large-bodied species and slightly under-represent diurnal species. Furthermore, this trapping technique is sensitive to several external disturbance effects (e.g., Merrett & Snazell 1983, Topping & Sunderland 1992, Sunderland et al. 1995, Hancock & Lang 2011, Zou et al. 2011, McCravy 2018). Nevertheless, pitfall trapping tends to represent the highest percentage of the surveyed taxa, inclu- ding rare species when compared to other sampling methods, making it almost essential for inventory studies (e.g., Chur- chill & Arthur 1999, Cardoso et al. 2008, Sabu & Shiju 2010). In contrast to pitfall trapping, D-Vac suction sampling is considered to have relatively high cost and labour require- ments, but it is far less sensitive to species activity and can provide a measure of arthropod density (McCravy 2018). On the other hand, it often under-represents large and heavy spe- cies, and species that frequently occur under the soil surface, vegetation or debris (Lang 2000, Elliott et al. 2006, McCravy 2018).This sampling process causes more disturbances (Sun- derland et al. 1995). Finally, both methods are sensitive to undergrowth cover (Sunderland et al. 1995, Zou et al. 2012, McCravy 2018). Because of the reasons listed above, D-Vac suction is not as popular as pitfall trapping, but it is still wide- ly used in entomological researches (Samu et al. 1997, Elliott et al. 2006). While there have been numerous studies dedicated to the comparison of pitfall trapping and D-Vac suction sampling re- garding various habitats, there have been none – to the best of our knowledge – that compared the two methods regarding ar- tificial gaps in forest ecosystems.Therefore, our main goal was to conduct such a survey, focusing on the following questions: 1. Is there any difference between the communities accessed by the two sampling techniques, especially regarding spe- cies and specimen numbers, family compositions, similari- ty- and diversity indices and body sizes? 2. Do the communities accessed by the two different me­ thods show differentiations between the two habitats (fo- rest stand and gaps)? 3. Considering our findings and field experiences, is one of the sampling methods more suitable than the other to sur- vey such study sites, or can they be used in a complemen­ tary manner? This contribution was presented at the 31st European Congress of Arachnology, Vác, Hungary, 2018 July 8–13 László BALI, Katalin TUBA, Institute of Sylviculture and Forest Protection, Faculty of Forestry, University of Sopron; Sopron, Hungary; E-mail: bali.laszlo@uni-sopron.hu, tuba.katalin@uni-sopron.hu Dániel ANDRÉSI, Institute of Sylviculture and Forest Protection, Faculty of Forestry, University of Sopron; Sopron, Hungary; KEFAG Ltd; Kecskemét, Hungary; E-mail: andresi.daniel@gmail.com Csaba SZINETÁR, Institute of Biology, Faculty of Natural Sciences, Eötvös Loránd University; Szombathely, Hungary; E-mail: szinetar.csaba@sek.elte.hu submitted 30.11.2018, accepted 19.7.2019, online 13.9.2019