The population ecology of some woodland carabid beetles, with particular reference to their dispersive behaviour

Abstract

The mobility of carabid beetles in the field has been studied by a number of researchers in recent years, but the small scale movements are still poorly understood. The populations of five species of carabid beetles living in a Surrey oakwood were therefore investigated using pitfall trapping and individual marking techniques over a period of three years.Five aspects of the complications associated with the interpretation of pitfall trapping and mark-release-recapture studies were investigated: (i) baiting of the traps by the catch itself, (ii) escape ability of captured beetles, (iii) changes in behaviour following overlong procedures between capture and release, (iv) density effects produced in trapping, and (v) effects of marking procedures on behaviour and survival. No effects could be demonstrated for (i), (iv) and (v). However, the escape rate in Nebria brevicollis was shown to be very high, and the behaviour of the same species affected by the length of time between capture and subsequent release.More than 3000 recaptures of marked beetles were made. Survival into a second breeding season was found to be commonplace in all five species; a few even entered a fourth. The distributions of the beetles within the study area were aggregated, particularly so in Nebria, where it was also shown that the beetles tend to remain in the areas where they are in the highest densities. Distributions changed little with season.Peak displacement rates were associated with the breeding seasonin Nebria but, whereas this fell off with the onset of winter in first season beetles, the level remained high in second season individuals. Pterostichus madidus exhibited a significant lack of displacement with time, except with males during the breeding season. Greatest activity and dispersal was found in August in first season males, but June and July with second season. Abax parallelepipedus beetles were found to be most active early in the season. Very few beetles of the species were found to disperse 100 metres or more within the study area. The concept of home range was examined in relation to ground beetles. Site attachment could not be demonstrated in any species, although other aspects of the trapping results indicated some form of home ranging behaviour.