Survival of Populations of Agonum Ericeti Panz. (Col., Carabidae) in Relation To Fragmentation of Habitats

Abstract

The stenotopic carabid species Agonum ericeti Panz. of peat moor habitats is unable to fly, and therefore cannot bridge distances that exceed 200 meters between sites suitable for reproduction. At present in Drenthe (The Netherlands) suitable habitat conditions for this species are restricted to some remnants of large peat moors and a few moist heath areas (say > 50 ha), on the one hand, and to a number of small and isolated peat bogs (in most cases <5 ha), on the other. By sampling 20 of these habitats in 1988 ('89), viz. 7 large habitats, 11 small ones and 2 intermediate sites, the presence of populations of A. ericeti could be established for all larger areas where the greater part of the surface consists of suitable habitat. Three of the habitats were also sampled in 1961 with the same result. However, after periods of between 24 and 66 years of complete isolation the species has become extinct in all but one small sites including two where it was still present between 1959 and 1962. From observations at Dwingelder Veld it could be concluded that in the larger habitats the species probably forms multipartite populations that to a certain extent are protected from extinction by spatial spreading of this risk over differently fluctuating subpopulations. In small habitats populations cannot be multipartite, and the survival time of such isolated populations is estimated at 7-44 years (mean 19 years) or less. This study gives a clear example where the area-effect of island biogeography, as far as it concerns rate of extinction, applies to habitat islands. A peaty upper layer of the soil seems to be a habitat condition that favours presence and survival of A. ericeti.

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