Distribution of the species Gammarus balcanicus and Gammarus fossarum on the territory of Serbia (central part of the Balkan peninsula)

Abstract

The results presented in this paper point to the need for a revision of the known distribution areas of the species Gammarus balcanicus and Gammarus fossarum, as well as of their contact zones, both on the territory of Serbia and on the Balkan peninsula as a whole. The occurrence of G. fossarum in western Serbia contradicts the assertion that G. balcanicus is the best represented species of this genus in western Serbia and indicates a considerably wider range for G. fossarum. The results presented herein undermine the previously held belief that G. fossarum is only sporadically encountered in Serbia (especially in southern and southeastern Serbia) and indicate that it is the most abundant and most frequently found species in the catchment area of the Southern Morava (southeast Serbia). Moreover, mixed populations of these two amphipods are encountered at the majority of the localities in the Southern Morava. It is here established that the zone of contact between G. balcanicus and G. fossarum is considerably wider than was imagined and in reality stretches into southern and southeastern Serbia: it was previously thought that the contact zone lies between the rivers Morava and Drina in western Serbia and on Mt. Kopaonik in central Serbia. Since G. fossarum is dominant in relation to G. balcanicus in the given region, it can be expected that future finds will further extend the zone of contact between these two vicariant forms to the south and southeast of the Balkan Peninsula.