Limnetica 38

Biases of taxa diversity and traits of source (active) and subfossil cladoceran communities with phylogenetic and functional approach were studied in two oxbows of the River Tisza, Hungary. Subfossil cladoceran communities were found to have suffered species loss due to both the degree of heterogeneity in the lake and taphonomical processes. The remains of heavily chitinized species are those most commonly found in the sediment, and therefore bias communities reconstructed on this basis. These biases are mostly caused by: (1) parts of soft bodied filterers (Daphniidae, Moinidae, Sididae (Diaphanosoma)), which are underrepresented in the subfossil remains of cladocerans, and (2) the remains of species that are difficult to collect and, so, underrepresented or absent in contemporary samples; this may have a strong effect on diversity indices. In spite of such biases, the paleocommunity does reflect the functioning of the ecosystem. The subfossil cladoceran community in the Morotva-tó (MT) corresponded to low fish densities and the high macrophyte coverage, indicating weaker top-down forces in this oxbow. The phylogenetic and functional approach to subfossil cladocerans may be useful in paleolimnological reconstruction, since phylogenetic and trait-based diversity indices correctly predicted top-down regulation as a function of the ecosystem.