Substitution patterns in congeneric arachnid species in the northern Alps

Authors


  • Present address: Staatliche naturhistorische Sammlungen, Museum für Tierkunde, A. B. Meyer-Bau, Königbrücker Landstrasse 159, 01109 Dresden, Germany. E-mail: christoph.muster@uibk.ac.at

Abstract.

Complementary abundance gradients of substituting congeneric arachnids along the northern margin of the Alps are described, and the possible historical and contemporary factors that have produced these distributions are explored. The intensities of activity of epigeous arachnids were determined in pitfall traps along seven altitudinal transects approximately 35 km apart in the Bavarian Alps (Germany) and in the county of Salzburg (Austria). No supraregional gradient of physical factors exists within the region investigated. Six pairs of congeners show vicariances or alternating abundance gradients. For each species pair, the abundance gradient is represented in diagrams and compared with a graphic model of substitution types. Three patterns are evident: strict vicariances, abrupt replacement in a narrow belt, and gradual substitution over a wide zone of sympatric occurrence. The different extent of range overlap suggests distinctive classes and intensities of interspecific interactions. With regard to biogeographic histories, one prevailing pattern emerged: endemic species of the eastern Alps are replaced by Eurosiberian counterparts towards the west. It appears that geographical abundance variation reflects colonization history.

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