On the significance of dispersal power for populations of carabid-beetles (Coleoptera, Carabidae)

Abstract

By various observations on carabid populations the author attempts to give an impression of the quantitative occurrence of dispersal and of the relation between dispersal and the chance of founding populations (dispersal power). Pitfall-catches in the recently reclamed "Zuiderzee"-polder E-Flevoland demonstrate that within seven years individuals of a number of monomorphic macropterous and dimorphic species had founded populations there. From the very high frequency of full-winged individuals within the latter populations it follows that full-winged carabid individuals generally must have a much greater power of dispersal than flightless ones. Therefore, winged individuals of dimorphic species were about equally able to reach E-Flevoland as were those of monomorphic macropterous ones, whereas individuals of monomorphic brachypterous species obviously are seriously hampered. The early appearance of individuals of riparian species on the shores of an artificial lake in the dune area "Meijendel" suggests that particularly populations living in unstable environments extensively "invest" in dispersal. It appears, however, that an important "investment" in dispersal apparently is not restricted to species from unstable environments; at least some sparse populations living in more stable environments also "sacrifice" relatively great numbers of individuals for dispersal (Pterostichus strenuus). The hypothesis is proposed, that populations facing a high risk of extinction generally will have a sufficient chance of founding populations (high "turnover") when "investing" extensively in dispersal. Not only macropterous but - at least in some populations - also brachypterous individuals participate in migration, although in the populations studied the dispersal power of flightless individuals is found to be very small (Carabus problematicus). Under certain conditions the dispersal of full-winged individuals from wing-dimorphic populations may ultimately lead to a decrease or even a loss of dispersal power by a decrease of the frequency of macropterous individuals. It is assumed, however, that under certain natural conditions also brachypterous individuals may contribute to the spreading of risk within and between populations. The dispersal power of monomorphic macropterous, dimorphic and monomorphic brachypterous populations in a cultivated countryside like Drenthe is discussed. The connection between the dispersal power of different kinds of carabid populations and the resulting chance of survival under different conditions is discussed. Some suggestions for nature preservation management are given.