A comparative study of the immigration of carabids (Coleoptera, Carabidae) into a new polder.

The immigration of carabids into the Lauwerszeepolder (constructed in 1969) was studied in 4 areas. These areas have different types of soil and consequently different vegetations. The carabid fauna was sampled by means of striptraps and window traps. In this way a total number of 116000 specimens was caught.A comparison of the catches shows great differences between the fauna in different study areas in successive years. The data are compared with those of another Dutch polder (IJsselmeer polder). It is shown that about 50% of all species caught are able to fly. Moreover it is demonstrated that relatively more specimens of sparse populations than of dense populations fly.The data, especially those on ovarian development, show that flight occurs mostly in early adult life. Moreover, flight muscle autolysis at the onset of ovarian development is a common feature among carabids. Females fly more readily than males. Whereas the flight of most species covers only short distances, some species fly across the borders of their habitats. The data suggest five categories in carabids with respect to flight.Brachypterous carabids were very rarely found in the polder. It is suggested that changes in the numbers of macropterous specimens in carabid populations outside the polder proper are not due to dispersal.The role of migration in the stabilization of carabid populations is estimated to be very small.