COMPARISON BETWEEN DEATH AND LIVING LAND MOLLUSK ASSEMBLAGES IN SIX FORESTED HABITATS IN NORTHERN ITALY

Abstract

In order to assess taphonomic pathways leading to preservation of land snail assemblages, the agreement between the death (DAs) and living assemblages (LAs) of land mollusk communities was evaluated in six forest habitats along an altitudinal and soil acidity gradient in Northern Italy, using data obtained by visual search and sorting of leaf litter and soil. Death assemblages were considered both as overall DAs and as DAs consisting solely of pristine (i.e., fresh) shells. Both calcareous and acidic soils showed high fidelity in richness and evenness, in particular leaf litter and soil samples, as can be expected in depositional environments with reduced time averaging. Lack of rank-order agreement in species relative abundance was observed in visual search (r = 20.37-0.45), while significantly high rank-order agreement (r = 0.61-0.89) in leaf litter and soil. Time averaging and interspecific variation in life span and in shell durability appear to determine the observed live-dead mismatch, which, in contrast, was probably not affected by between-habitat transport and temporal changes in community composition. Between-habitat differences are generally preserved in the DAs. DAs based on pristine shells do not show higher rank abundance correlations and smaller differences in ordinations than DAs based on all shells. But in terms of species richness and evenness, DAs composed only of pristine shells were more similar to the LA, in particular in leaf litter and soil, supporting terrestrial ecologists' approach in considering pristine shells in inventories of species richness. Distinguishing between pristine and worn empty shells is especially useful for actualistic studies in highly calcareous sites, where DAs are expected to encompass a longer temporal duration.