Monitoring arthropods in protected grasslands: comparing pitfall trapping, quadrat sampling and video monitoring

When monitoring the activity and diversity of arthropods in protected areas it is ethically advisable to use non-destructive methods in order to avoid detrimental effects on natural populations and communities. The aim of this study was to compare the efficiency of three methods for potential use for arthropod monitoring in a protected grassland: pitfall trapping, quadrat sampling and video monitoring. Pitfall trapping was conducted either during the day or over night (cup diameter 6.5 cm, unfenced, without preservation fluid). Quadrat sampling was conducted within a metal frame (width × length × height: 50 × 50 × 30 cm). Video monitoring was done on a 68 × 37 cm area using a digital high-density video camera mounted on a tripod. The study site was located in a semi-dry grassland northwest of Vienna, Austria (305 m a.s.l., 48°27′ E, 16°34′ N); the three methods were replicated five times. Across the sampling methods a total of 24 arthropod orders were observed with Hymenoptera being the most abundant, followed by Diptera and Coleoptera. The sampling methods differed considerably in number of arthropods recorded: video monitoring (2578 individuals) followed by quadrat sampling (202 individuals), nocturnal (43 individuals) and diurnal pitfall trapping (12 individuals). Diversity of arthropod assemblages varied highly significantly among the tested methods with quadrat sampling yielding the highest diversity 0.70 ± 0.22 (Gini–Simpson index, mean ±SD) followed by video monitoring (0.57 ± 0.15), diurnal pitfall sampling (0.35 ± 0.28) and nocturnal pitfall sampling (0.17 ± 0.24). Video surveillance of the pitfall traps showed that out of a total of 151 individuals crawling in the vicinity of pitfall traps none of them were actually trapped. A tabular comparison listing the advantages and disadvantages of the sampling methods is presented. Taken together, our results suggest that video monitoring has a great potential as a supplementary method for quantitative and qualitative assessments of arthropod activity and diversity in grasslands.