Shifting average body size during regeneration after pollution - a case study using ground beetle assemblages

1. Pitfall data, collected periodically between 1980 and 1996, were used to analyse the spatial and temporal body size pattern of ground beetle assemblages (Carabidae) in a former polluted grassland. 2. Two hypotheses were tested: (i) Siemann et al.'s efficiency-specialisation hypothesis that predicts that during succession (or regeneration) processes the mean body sizes of consumer assemblages decrease and (ii) Blake et al.'s hypothesis that predicts that smaller body sizes are found with increasing level of disturbance. 3. Biovolume was considered as a determinant of ground beetle body size. This was analysed by using a digital-optical volume measurement. The mean error associated with the idealisation of the ground beetle body shape as an ellipsoid was determined as 10.24 +/- 2.5%. 4. A significant decrease in average ground beetle body size was recorded in moving from the pollution (1980) to the post-pollution (1996) period. The mechanisms linked with ecological succession after factory closure (1990) were discussed as the main causal factor sustaining Siemann et al.'s hypothesis. 5. The analyses of the mean body size during the transition period from the pollution to the post-pollution period demonstrate that Blake et al.'s hypothesis was also partly supported, and may overlay the effects driven by succession. 6. It is therefore concluded that both hypotheses may be used to explain not only the change in body size from a highly polluted to a less polluted area, but also the relationship between habitat structure and predatory ground beetles.