Local numbers of ground beetle species of heathland appeared to be significantly associated with size of total area, whereas such relationships were not found for the total number of ground beetle species and eurytopic ground beetle species. Presence of species with low chances of immigration was highly associated with area. This is accordance with the "area per se" hypothesis for islands as far as extinction rates are concerned. The habitat diversity hypothesis and the random sampling hypothesis are of less importance for explaining this phenomenon. The importance of dispersal for presence and survival in fragmented habitats could be demonstrated. This result supports the founding hypothesis, under which founding of new populations is considered the main effect of dispersal. The frequency of heathland species with low powers of dispersal in habitats smaller than 10 ha was 76% lower on average than in areas larger than 100 ha. For heathland species with high powers of dispersal this frequency was only 22% lower on average. The period of isolation of the habitats studied, 26-113 years, appeared to be too long to persist for many populations of heathland species with low powers of dispersal.

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We deal with the causes of the synchronously fluctuating numbers of subpopulations of the carabid species Calathus melanocephalus as compared with the asynchronously fluctuating numbers of subpopulations of the carabid Pterostichus versicolor. Both species continuously occupy a large heath area, Dwingelder Veld (1600 ha), in The Netherlands, and are studied there in the same localities with the same methods. Of the adults of C. melanocephalus, 90% do not cover more than 2 ha during the entire reproductive season, while 90% of adults of P. versicolor cover no more than 12 ha. In C. melanocephalus egg production in the field is usually similar to that under optimal feeding conditions in the laboratory, but in P. versicolor egg production seems to be much lower in the field. In the field 70-80% of the eggs most probably are killed by eelworms, followed by more than 90% mortality among the remaining larvae. Comparing mortality of developmental stages in laboratory experiments with that in field experiments in enclosures, it appears that mortality of larvae is not density-dependent, even when density in the experiments is much higher than it ever is in the field. Larval mortality mainly results from the poor ability of the larvae to find prey, even when in field experiments prey density is increased far above natural densities. We discuss why these poor prey-finding abilities are not improved by natural selection. In the spring breeder P. versicolor differences between localities both in abiotic factors, soil moisture and surface temperature, and biotic factors, reactions of prey species to abiotic factors, in spring and summer when the larvae are maturing contribute to the asynchronous fluctuations of numbers between subpopulations. In the autumn breeder C. melanocephalus possible differences in biotic factors between sites are outnumbered by the effects of winters with a higher or lower than normal amount of precipitation respectively. During a wet winter mortality among the larvae is much higher than during a dry winter. As these winter conditions are similar over large areas (many km) the fluctuations of numbers between subpopulations are synchronous.

Abstract. The relative influences of temperature and availability of food on reproduction, survival and growth of all developmental stages of two carabid beetle species are discussed with special reference to the suggested relationship between availability of food, size of egg production and survival of adults from one breeding season to the next. Temperature as well as food supply influence the length of larval growth and adult body size. Beetles grown at low temperatures and low amounts of food are smaller than those grown at higher temperature and with more food. The number of eggs laid per female was correlated with the amount of food gathered. There was no inverse relationship (trade‐off) between reproductive output and survival in the field until the next breeding season. In 1980 no significant relationship was found between winter mortality and the amounts of food gathered by beetles in the period after reproduction and before winter diapause. However, in 1981 in C. melanocephalus a lower number of starved beetles survived the winter than the fed ones and‘field’beetles. Only in the first part of the feeding activity period in autumn can enough food be gathered by C.melunocephalus for successful hibernation. In the second part of this period there is not enough food to build up the fat reserves needed to survive the winter. Difference in population fluctuations of both species are discussed in relation to their life histories.