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

Abstract

SummaryThe 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.