DIGGING OUT THE DIGGING-IN EFFECT OF PITFALL TRAPS - INFLUENCES DEPLETION AND DISTURBANCE ON CATCHES OF GROUND BEETLES (COLEOPTERA, CARABIDAE)

We examined the extent to which depletion of local carabid populations and disturbance of trap sites can influence estimates of overall catc h, seasonal occurrence, and community structure of carabid beetles tha t are obtained using pitfall traps. A 3 x 3 factorial experiment was u sed, wherein trap stations were placed at three distances from one ano ther (10, 25 or 50 m), and were subjected to three different trapping methods (permanent, disturbed, or revolving) over 8 weeks in 1993. Ove rall, fewer carabids were captured in traps at the 10 metre spacing (i ndicating depletion occurred) and in permanent traps (indicating a dis turbance effect), but responses to treatments varied among the four mo st abundant species. Permanent traps and those at the 10 metre spacing were less sensitive to changes in activity over time, and both types of treatments generated patterns within trapping periods as well as ov er the course of the entire experiment. The most similar species assem blages and the fewest rare species were found in traps at the 10 metre spacing; disturbed traps had higher species richness but lower evenne ss than permanent traps. These results suggest that disturbance and de pletion can affect pitfall catches of carabid beetles in forest enviro nments. This information should aid in the design of pitfall studies w ith minimal unknown bias.