Arachnologische Mitteilungen 58

24 L. Bali, D. Andrési, K. Tuba & C. Szinetár Materials and methods Study sites and methods Our data collection was carried out in West Hungary, near the town of Vép in the Gyöngyös-plain (47.22750°N, 16.78917°E, 190 m a.s.l.). The mosaic-like landscape struc- ture of this region consists mainly of agricultural fields, per- manent grasslands with anthropogenic influence (mowing) with natural vegetation, and forest patches. The studied sub- compartment was a homogenous turkey oak ( Quercus cerris L. 1735) stand, aged 70 years (in 2014), containing 12 arti- ficial gaps (#1–#12) opened in 2010 (approximately 15 × 30 m) (Kollár 2017). Only the gaps had understory, which was densely populated by turkey oak saplings and Rubus patches. Everywhere else, the forest floor was covered with threads of Poa species and thin leaf litter. The forestry climate category of the subcompartment is hornbeam-oak.The elevation of the terroir is 200 m, with plain geomorphology. Topsoil is deep, consisting of brown forest soil with pise texture and has no excess water. We surveyed two artificial gaps (#7 and #9) of the sub- compartment, and the stand around them, with double-cup- ped Barber-type pitfall traps (PT) (Barber 1931, Woodcock 2005, Kádár & Samu 2016). They had a diameter of 90 mm at the top, and were filled with 10% acetic acid solution as a preservative. In each gap, the traps were positioned in 70 m long transects along the longitudinal axis of the gaps, with 15 traps in each transect, 5 m apart from each other. Traps N o 5 and N o 11 were at the approximate edges of the gaps (Fig. 1). Emptying of these traps took place once, after two weeks of field use, on 24. Jun. 2014. The D-Vac suction sampling (DV) (Dietrick 1961) was carried out on 24. Jun. 2015. We surveyed six additional gaps (#1, #2, #4, #6, #10 and #11). At each gap, we sampled five, 0.1 m 2 areas, starting from the centres of the gaps, 5 m apart from each other, with double repetition (Fig. 1.). We chose this sampling layout of the suction sampling for the following reasons. We intended to have the same sample size (30), as the pitfall trapping (we consider the ‘A’ and ‘B’ transects re- petitions of each other). We also believed that surveying the gaps and transects of the original pitfall trapping would be suboptimal, since the samplings we conducted there in previ- ous years were quite extensive, which could have influenced a new sampling. Finally, since the D-Vac sampling took place during only a single day, we intended to survey as many addi- tional gaps as possible, to mitigate the unforeseeable negative effects that may occur during samplings (e.g. anthills, fallen dead wood, big game activity, etc.). The specifications of the used suction device (Stihl SH86) are as follows: a 0.8 kW (or 1.1 hp) 27.2 cm 3 petrol engine with 7200 rpm speed, 770 m 3 /h suction capacity. A 2 litre, densely woven textile bag was used for sample collections.This device is similar in principle to the one used by Samu & Sárospataki (1995). In common field practice, pitfall traps are generally used for weeklong intervals, while an individual vaccum sampling only lasts for minutes. We choose to follow these practices in our survey. Since our present study is part of a larger, complex survey of the sub-compartment (Kollár 2017), we decided to keep and include the original designations of the gaps. Data analysis Given that we did not have the same number of samples in the different habitats, we will not make direct comparisons between their explored communities. Instead, our aim was to compare either individual samples (usually every sample, with every other sample), or the total data of both methods. We analysed the following data: numbers of species (S) and spe- cimens (n), family and guild composition, and average body sizes [mm], which were identified by using literature data for every species (Nentwig et al. 2018). We also calculated the Shannon (H’) diversity (based on natural logarithms), which is known to be sensitive to undersampling (May 1975, Beck & Schwanghart 2010), but we consider the surveyed commu- nities well explored. To calculate this index, only data from mature specimens were used. Fig. 1: Arrangement of the pitfall traps (top) and D-Vac suction samplings (bottom) at each gap (top view). Gaps represented as dark rectangles Tab. 1: Changes in community attributes along the sampling transects. Samples located at the same relative positions in the transects are summa- rized. Species (S) and specimen (n) numbers represented as percentages of the total catch results (PT – pitfall trapping; DV – suction sampling, d – the distance of the sample from the centre of a gap [m]; H’ – Shannon diversity; [mm] – body size; samples located inside gaps are bold ) Sample d S n H‘ [mm] PT.1 35 11.76  5.28 0.89 4.85 PT.2 30 14.71  2.16 1.20 5.62 PT.3 25 11.76  3.02 1.15 5.77 PT.4 20 23.53  2.05 1.89 5.34 PT.5 15 26.47  4.85 1.73 5.12 PT.6 10 38.24  7.11 2.03 5.03 PT.7  5 47.06 14.87 2.21 5.08 PT.8  0 35.29  5.28 2.24 5.55 PT.9  5 47.06  9.16 2.47 4.92 PT.10 10 26.47  6.25 1.38 5.15 PT.11 15 23.53 14.22 1.50 5.80 PT.12 20 44.12  9.81 2.08 5.71 PT.13 25 38.24  7.00 2.08 4.80 PT.14 30 20.59  5.28 1.33 4.90 PT.15 35 29.41  3.66 1.85 5.58 DV.1 45 41.46 14.99 2.66 2.66 DV.2 30 36.59 16.67 2.46 3.56 DV.3 15 34.15 18.66 2.34 2.41 DV.4 7,5 58.54 23.84 3.01 2.01 DV.5 0 43.90 25.84 2.68 1.86