The sedimentary strata of the Great Plains record the biotic and climatic events of the late Cenozoic era. Some of the best sedimentary exposures can be found in southwest Kansas. Kansas thus serves as a natural laboratory for examining patterns of biotic and climatic change through time. Twenty-six fossil molluscan assemblages were sampled from Pliocene and Pleistocene sedimentary strata (4.71-0.01Ma) near Meade, Kansas (lat 37o17’08”N., long 100o20’23”W.) in addition to the extant assemblage (0Ma). Sixty-seven taxa of freshwater and land gastropods and sphaerid bivalves are represented in these assemblages. The assemblages were examined for historical patterns in biodiversity: Local habitat was analyzed via a habitat ratio to estimate which assemblages were aquatic and which were terrestrial. Alpha diversity was examined as taxonomic richness and dominance (reciprocal of Simpson’s Index). Beta diversity was examined as taxonomic turnover (Jaccard Index) through time. For both alpha and beta diversity it was assumed that a “modernizing” trend existed; that is, biodiversity of southwest Kansas nearly five million years ago was unlike the extant assemblage but gradually came to become the extant assemblage as time progressed.
Results/Conclusions
Results for habitat ratio indicate that assemblages FAL, RFX, R1A, CR7, and M35 imply aquatic conditions (lentic or lotic systems or a terrestrial system with abundant meteoric water); all other assemblages imply more xeric conditions, thus the habitat of southwest Kansas changed over time. Biodiversity at both alpha and beta levels do not fit a modernization model but instead suggest random fluctuations through time. This is reflected in the low r2 values for alpha and beta diversity vs. time: richness (r2 = 0.237), dominance (r2 = 0.113), and turnover (r2 = 0.024). The data suggest that molluscan assemblages may be randomly assembled (open communities) with taxonomic composition governed by chance dispersal events.
