The Danube restoration project: Species diversity patterns across connectivity gradients in the floodplain system

The relationship between hydrological connectivity and species diversity pa tterns (alpha and beta diversity) of macrophytes, molluscs, odonates and am phibians was investigated in a semi-natural floodplain segment in the 'Allu vial Zone National Park' of the Danube River in Austria. Based on environme ntal variables, we distinguished four major channel types (inflow channel, parapotamal, plesiopotamal and palaeopotamal) that reflected a lateral conn ectivity gradient. In addition, a longitudinal environmental gradient along the parapotamal channel was found. Connectivity, rather than the surface area of individual floodplain water b odies, explained local species richness. Species diversity patterns varied among tars: the highest species richness values for molluscs occurred in th e parapotamal channels, for odonates in the para- and plesiopotamal channel s, for macrophytes in the plesiopotamal channels and for amphibians in the palaeopotamal channels. Within the parapotamal channels, the species richne ss of odonates and amphibians increased moving upstream. Beta diversity dis played an almost inverse relationship with alpha diversity, with highest av erage values in isolated and fragmented floodplain channels. Habitat fragme ntation favoured the beta diversity of most groups, although connectivity f avoured the beta diversity of amphibians. The highest proportion of endange red species (mainly rheophilic forms) was found in the parapotamal channels . It is concluded that preservation of the high diversity of this alluvial fl ood plain would be more fully realised by reconstitution of fluvial dynamic s and the associated connectivity gradients, rather than by restoration str ategies for individual groups or endangered species. Copyright (C) 1999 Joh n Wiley & Sons, Ltd.