Comparison of polyethylene bubble wrap and corrugated cardboard traps for sampling tree-inhabiting spiders

In this paper,we studied the use of polyethylene bubble wrap and corrugated cardboard bark traps to sample spiders inhabiting tree trunks, with special reference to test whether they function the same way despite the differences in the spider community imposed by the different tree species and surroundings and times of sampling. The survey was carried out from July 1997 to July 1998 in Turin, Italy, in a green urban area on three poplars and four American basswoods. Differences between the two methods were tested in terms of abundance, diversity, dominance, mean body length of specimens, and proportion of juveniles, calculating Spearman's correlations. Three-factor analysis of variance, multiresponse permutation procedure, and indicator species analysis were used for further analysis. Results obtained by the two traps were correlated following a similar trend over sampling time. Bubble polyethylene seemed to be more effective than corrugated cardboard at trapping higher number of specimens. The dimension and total amount of interstices and the different microhabitat conditions of temperature and humidity seemed to be the main factors influencing spider composition in terms of the selected variables. On the basis of our results, polyethylene bark traps are recommended for sampling spiders living on trees. It is important to consider seasonality in experimental design, autumn being the period with the highest abundance of spiders but a lower level of diversity