Ecological disparity is more susceptible to environmental changes than familial taxonomic richness during the Cretaceous in the Alpstein region (northeastern Switzerland)

Abstract

Studies of global palaeoecology through time usually ignore regional details. Such regional studies on palaeoecology are required to better understand both regional- and global-scale palaeoecolgical changes. We analyzed the palaeoecolgy of a Cretaceous sedimentary sequence in the Alpstein (cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden and St. Gallen, northeastern Switzerland), which covers from the Barremian to Cenomanian stage. Two diversity indices of familial taxonomic richness and ecological disparity (ecospace occupation) with the trophic nucleus concept were employed in order to document changes in palaeocommunities through time. Our results illustrate that taxonomic richness did not change dramatically, while distinct changes occurred in ecospace occupation through time. The changes in ecospace utilization likely root in fluctuations in water depth and ocean temperature. In addition to these changes in sea level and temperature, our results suggest that water depth was higher in the eastern part of the Alpstein region. Ecospace occupation was moderately diverse through time, which is likely linked with the favorable conditions such as moderate water depth, which made the region habitable for a range of organisms. Only during the late Barremian, the sea was maybe too shallow, thus preventing highly diverse associations. Statistical tests indicate that the chronological changes of familial taxonomic richness and ecological disparity are decoupled and that the ecological disparity is more highly variable in response to environmental changes than familial taxonomic richness.