The spatial dynamics and movement of Pterostichus melanarius and P. madidus (Carabidae) between and within arable fields in the UK.
The spatial dynamics of two important generalist predators (Pterostichus melanarius and P. madidus) was investigated across six fields encompassing 64 ha of arable land. Their spatial distribution was monitored using a grid of 973 pitfall trap locations during two years. Movement and population density were estimated using mark-release-recapture across six fields in 2000 and across the three smallest fields in 2001 . Both species exhibited strong aggregation into patches but the location of these differed between the species. The location of the patches varied between years for P. madidus, which favoured pea compared to cereal crops. P. melanarius exhibited a more restricted but stable distribution within and between years. Overwintered adults of both species were associated with the field margins early in the year whereas most tenerals emerged within the field. On average, the daily displacement distance of P. madidus was twice that of P. melanarius. There was no difference between the sexes in the daily displacement or total distance moved. P. madidus crossed field boundaries more frequently than P. melanarius. P. madidus had a very high population density in 2000 with peak numbers of 5.8 m-2 whereas that for P. melanarius was 0.3 m-2. In 2001 the peak density of P. madidus was 0.7 m2. The importance of field boundaries and farming practices to the spatial dynamics of these two species are discussed.