A faunistic review of the modern and fossil molluscan fauna from Lake Pamvotis, Ioannina, an ancient lake in NW Greece: implications for endemism in the Balkans

The Balkans are justifiably famous for being natural hotspots of floral and faunal biodiversity and endemism. Much of this biological diversity is witnessed in the ancient lakes that exist (or previously existed) in the region, which have provided stable, long-lived arenas within which evolutionary processes have been able to operate. One group that ably demonstrate such diversity are the gastropod molluscs. Their wide dispersal, morphological variability and relative ease of identification make them ideal candidates for addressing questions concerning patterns and processes of biodiversity and evolution over time (e.g. Michel, 1996). Furthermore, the fact that they are often well preserved in fossil sequences means that they can provide a temporal dimension to evolutionary investigation, something that is often difficult to resolve when using groups more traditionally associated with this kind of work, such as the cichlid fishes. The molluscan faunas of the Balkans (and Greece in particular) have been the subject of study for at least the last two centuries (e.g. Butot & Welter-Schultes 1994). Isolated ancient lakes from the region, and in particular Ohrid, have often been a focus for detailed investigation, because of their remarkable endemic faunas (e.g. Hadzisce, 1956; Hubendick & Radoman, 1959; Stankovic, 1960; Meier-Brook, 1983; Stankovic, 1985; Schtt, 1987; Sattmann & Reischtz, 1988; Dhora & Welter-Schultes, 1996). Despite this, the malacology of many other key localities from the area still remains poorly documented. In this paper we first briefly review the main controls thought to influence the radiation of gastropods in ancient lakes and then present the modern and fossil aquatic molluscan fauna from a typical but previously poorly known site: Lake Pamvotis, located in the Ioannina Basin in NW Greece. Comparisons are then drawn with the gastropod fauna derived from other extant and fossil ancient lakes from across the Balkan region (bivalves are considered by Korniushin elsewhere in this volume), before highlighting some common patterns and providing some thoughts on the implications for speciation in ancient Balkan lake systems.