The importance of connecting isolated habitats illustrated at carabid populations; P .J. den Boer

To help solving persistent controverses and hot discussions around the regulation of animal numbers, survival of small populations and competition between species among ecologists in 1959 the author started from the Biological Station Wijster comparative, long-term investigations into the dynamics of carabid populations. He mainly concentrated his work at the large (1600 ha) heath area Dwingelderveld (Kraloërheath), where he discovered the principle of stabilization of numbers by ‘spreading the risk of local extinction’ over interaction groups (subpopulations) as an alternative for the more generally accepted idea of ‘regulation of animal numbers’. In this paper the author mentioned what happened with some of the carabid species he studied in the course of more than 40 years in this heath area under gradually changing environmental conditions (details in Den Boer & van Dijk, 1994) to show the importance of the ‘Plan Goudplevier’ of Natuurmonumenten for connecting isolated habitats.

The Mantingerveld: effects of fragmentation and defragmentation followed using carabid beetles; H.J.W. Vermeulen, A.J. Spee & R.J. Popken

In 1958 the reclamations of heathlands and drift sands in the area of Mantingerveld (Netherlands, centre of province Drenthe) came to an end, leaving 300 ha of fragments scattered over this area. In 1992 several arable lands between those fragments were bought and restored by removal of the nutrient-rich topsoil layer. The effects of both fragmentation and defragmentation were followed by the Biological Station and compared to a large not fragmented area, the Dwingelderveld. Ground beetles were used as indicator species for the soil fauna. In 1959 at the Dwingelderveld and in 1963 at the Mantingerveld the first pitfall traps were placed; the sampling series were continued up till now. Although at both areas some species were lost due to overall working factors, in the Mantingerveld more species disappeared. After the restoration there was a slight growth in number of individuals in the fragments and some species were caught in the new areas. Also new heathland and drift sand species were caught. As the amount and quality of habitat increased, it is recommended to reintroduce the non-flying species or to introduce transplantates to give the entire poor dispersing soil fauna a chance.

 

A large heathland part of ´Plan Golden plover´ in Drenthe, the Netherlands

 

Ten years after the start of 'Plan Golden plover'; B.F. van Tooren, H.J.W. Vermeulen, R.J.H. Douwes & H.L. Schimmel - ten Kate

Ten years ago a plan was developed to connect four small nature reserves in the north of the Netherlands, mainly with heathland and woodland, by transforming the intensively used grassland between these reserves into heathland, extensively used grasslands and open water. Totally c. 650 hectares should be transformed into nature. Nowadays, 475 hectares new nature area has been achieved including 195 hectares where the nutrient rich top soil already has been removed. Main goals of the plan were to enhance the nature values of the existing nature reserves and to create more possibilities for dispersion of species between these nature reserves. A third goal was to develop interesting nature between the existing nature reserves. The main result after ten years is that many hectares of grassland, where large amounts of fertilizers were used and where large negative effects on the water table in the surroundings existed, has been transformed into a more natural area. There are indications that the value of the existing nature in the reserves is increasing, for example for birds and carabid beetles. Until now the new nature has invaded only slowly by most species, mainly because the development of the vegetation is rather slowly. Interestingly, there are large differences between different animal groups. Whereas carabid beetles are invading rapidly, ants avoid the new nature since the frequently still bare soil does not offer any comfort to these species. Also rare plant species invade the newly created nature only very slowly, probably due to the absence of seeds of these species in the soil and the poor dispersal capacities of most species. More time is needed to obtain sufficient dispersal possibilities for many species.