Das lokale Ausbreitungsmuster der Wustenspinne Seothyra henscheli - ein raumlich-explizites gitterbasiertes Simulations-modell

The distribution pattern of the dune-burrowing spider S. henscheli (Eresidae) is clustered at two spatial scales in the Namib Desert (HENSCHEL and LUBIN 1997). First, only the sandy areas are densely inhabited by spiders and secondly, within these areas they are locally clustered. These sandy dunes are often separated by areas in which the conditions are less favourable for S. henscheli. We ask how S. henscheli has spread and invaded new areas, considering the weak dispersal potential of this spider. A grid-based simulation model was developed to explain the local distribution pattern and the way in which S. henscheli has spread over long distances. Simulations support the idea of HENSCHEL and LUBIN (1997) that the locally high densities can be explained by short distance dispersal and that they are not a result of habitat features. Field data and simulation runs show that these structures are not spatially invariable, but change with time. We classified the burrows of S. henscheli in clusters and measured the velocity of these clusters in further simulation runs. The velocity was low (<1.5 m/year) which leads us to the conclusion that wandering of whole clusters is unlikely to explain the spread of S. henscheli over long distances.