Effects of mowing on body size patterns in spider assemblages of mesic meadows

Habitat disturbance affects not only the abundance, species richness and species composition of the local fauna, but also the body size of specific individuals and body size patterns in animal assemblages. Particularly large disturbances occur in agroecosystems, where many agricultural treatments are carried out. One of them, which is most commonly applied to grasslands and which significantly damages the habitat structure, is mowing. We examined the effect of mowing on mean, skewness and kurtosis of the body size in epigeic spider assemblages. The research was conducted on mesic meadows in eastern Poland, in an agricultural landscape typical for this region, consisting of a mosaic of meadows, fields and forests. Spiders were collected using pitfall traps in two sampling periods: the first before mowing and the second when part of the meadows had been mown. Mowing had no significant effect on mean body size, skewness and kurtosis of the body size in epigeic spider assemblages. However, after the cut, mown plots showed, on average, significantly smaller spider species than unmown plots. Both the value of skewness and kurtosis significantly increased after mowing but to the same extent on both the control and mown plots. The decrease in mean body size and increase in skewness in spider assemblages were mainly due to an increase in the number of small species from the Linyphiidae family. It is likely that these species began to migrate (via ballooning) during the second sampling session, following the start of haying, and were thus caught in traps more frequently. Our study showed no clear, significant changes in the body size structure of epigeic spiders in mown meadows compared to unmown ones, which may suggest that the mowing, where extensive farming is practised, does not have a long-term significant negative impact on this group of invertebrates.