Arachnologische Mitteilungen 58

Suction sampling vs. pitfall trapping in gaps 27 and/or web-building specimens. Examining the family struc- tures, Linyphiidae was more represented in the D-Vac sam­ ples, while Lycosidae and Gnaphosidae were more represented in the pitfall samples. Underrepresentation of Lycosidae in D-Vac samples has been reported in multiple studies (Merrett & Snazell 1983, Dinter 1995). The distribution of body size data showed that the pitfall traps could catch larger species on average, as has been shown in several previous papers (Sun- derland et al. 1995, McCravy 2018).The changes in commu- nity characteristics along the transects, and the results of the regression analysis show that the effects of the gap openings were more prominent regarding species numbers, specimen numbers and diversity indices, especially using pitfall traps. Multiple reasons may have caused the differences obser- ved between the sampling methods. One of the more obvious is the duration of each sampling. While pitfall traps were ac- tive for 14 days (and nights), the suction sampling took place during one day (in daytime). This means that less abundant and/or nocturnal species (i.e. Gnaphosidae) are more likely to be caught by pitfall traps.The disturbance (vibrations) caused by the suction device may also be responsible for the under- representation of hunting spiders (i.e. wolf spiders) in these samples. In addition, smaller and lighter species (Linyphi­ idae) may be easier to catch using suction sampling, which is in line with the findings of Mommertz et al. (1996). In addi- tion, the D-Vac suction may unable to access those specimens that are under debris (leaf litter, dead wood, stone), or in the topsoil at the time of the samplings (Sunderland et al. 1987). In summary, we suggest that for ground-dwelling spiders in forest ecosystems – partly because of its habitat’s higher structural complexity – the D-Vac suction sampling is more suitable for short-term examinations, while pitfall traps can more effectively conduct the research requiring longer dura- tions. Overall, both methods seem to be adequate to explore the effects of gap openings, but they access somewhat diffe- rent attributes of the spider community. Pitfall trapping was more sensitive towards larger and/or active hunting species, while suction sampling resulted a higher abundance of web building and/or smaller species. Therefore, in order to gain a more detailed picture on the ground-dwelling spider commu- nity of a given area, we suggest their combined use, perhaps with a pitfall focus due to this cheap maintenance and low labour requirements. Acknowledgements We are thankful for the assistance of colleagues from the NAIK ERTI. This study was carried out within the programs ‘TÁMOP- 4.2.2.A-11/1/KONV-2012-0004’ & ‘VKSZ_12-1-2013-0034 - Agrárklíma.2’. References Anderson MK &Willis TJ 2003 Canonical analysis of principal co- ordinates: a useful method of constrained ordination for ecology. – Ecology 82:511-525 – doi: 10.1890/0012-9658(2003)084[0511:ca- opca]2.0.co;2 Barber HS 1931 Traps for cave-inhabiting insects. – Journal of the Elisha Mitchell Scientific Society 46: 259-266 Beck J & SchwanghartW2010 Comparing measures of species diver- sity from incomplete inventories: an update. 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Non-metric multidimensional scaling (NMDS) based on Bray-Curtis dissimilarity. Dots represent the sampling sites in the transects, with minimum spanning tree. Samples located at the same rela- tive positions in the transects are summarized (PT – pitfall trapping; DV – suction sampling; circles – forest located samples; squares – edge located samples; triangles – gap located samples) Tab. 4: Linear regression analysis. We considered relationships to be significant at P < 0.05 values (D – distance from the centre of the gaps; independent va- riable; I – intercept; n – specimen number; S – species number; [mm] – average body size; H’– Shannon diversity; PT – pitfall trapping; DV – suction sampling) PT DV R 2 P I D R 2 P I D n 0.1466 0.0367 45.7368 -0.7930 n 0.1376 0.0436 51.6882 -0.5071 S 0.3480 0.0006 9.3421 -0.1576 S 0.0361 0.3147 4.7902 -0.0303 [mm] 0.0010 0.8708 5.2534 0.0015 [mm] 0.1152 0.0665 1.6619 0.0216 H‘ 0.3843 0.0003 2.0101 -0.0250 H‘ 0.0460 0.2549 1.3711 -0.0072 0.225 0.150 0.075 0.000 -0.075 -0.150 -0.225 -0.300 -0.2 -0.1 0.5 0.4 0.3 0.2 0.1 0.0