DECOUPLING OF COMPOSITIONAL AND ENVIRONMENTAL FIDELITY IN DEATH DIATOM ASSEMBLAGES FROM SHALLOW LAKES

HASSAN, GABRIELA S.

Mendoza

Congreso; 4th International Paleontological Congress; 2014

IANIGLA, CCT-CONICET Mendoza

Comparisons between death assemblages and their source living communities are among the most common actualistic methods of evaluating the preservation of compositional and environmental information by fossil assemblages. While live-dead studies have been commonly focused on marine mollusks, the potential of diatoms to preserve ecological information in continental settings has been overlooked. This lack of knowledge on the nature and magnitude of the taphonomic biases affecting live-dead agreement of diatom assemblages contrasts significantly with their extensive application as modern and fossil bioindicators in paleoecological and paleoenvironmental reconstructions. In this study, three live-dead datasets are analyzed in order to evaluate the compositional and environmental fidelity exhibited by death diatom assemblages in shallow lakes. Compositional fidelity was assessed by comparing richness, diversity and abundances of seasonally collected living (LAs) and death (DAs) assemblages through multivariate techniques. Environmental fidelity was evaluated by analyzing the relationship between LAs and DAs and environmental variables, and comparing the performance of both analyses in terms of explained variance and statistical significance. I find that death diatom assemblages do differ significantly in their taxonomic composition from living assemblages, mainly as a consequence of (1) differences in the temporal resolution between time-averaged DAs and non-averaged LAs, and (2) differential preservation of diatom taxa related to the intrinsic properties of their valves. Besides compositional dissimilarities, DAs were able to capture the same environmental gradients than LAs with high significance. This decoupling between live-dead agreement in community composition and community response to gradients can be related to the existence of at least two mutually exclusive subsets of species that significantly captured compositional dissimilarities based on the full set the species in the three lakes. This functional redundancy implies that the between-sample relationships of living assemblages can be significantly preserved by DAs even if some taxa are removed by taphonomic processes. Hence, as the preservation of environmental gradients does not require a good preservation of all living taxa, structural redundancy compensates the loss of compositional fidelity caused by postmortem processes in this diatom dataset.