Density, distribution and dispersal of the carabid beetle Nebria brevicollis in two adjacent cereal fields

The distribution of the carabid beetle Nebria brevicollis was monitored in the summer during a period of declining activity associated with aestivation in a hedgerow. After emergence from aestivation, population density, distribution and dispersal of N. brevicollis were studied during autumn 1994 in a mark-recapture experiment. 3560 beetles were marked and 1887 were recaptured in a grid of pitfall traps spanning a hedgerow and extending approximately 32 m either side into two recently harvested cereal fields. Population size, estimated from a Lincoln index, increased slightly with time with a mean population density of approximately 0.9 beetles m(-2) Activity-density varied during the experiment and was significantly related to maximum temperature. The population was aggregated within the hedgerow during aestivation and in several spatially stable hot-spots of activity-density within the field during autumn. There was considerable movement within fields but the hedgerow was a significant barrier to dispersal between fields, with potential effects on the metapopulation structure of the species.