Life span bias potentially alters species abundance in death assemblages through the overrepresentation of short-lived organisms compared with their long-lived counterparts. Although previous work found that life span bias did not contribute significantly to live–dead discordance in bivalve assemblages, life span bias better explained discordance in two groups: longer-lived bivalve species and species with known life spans. More studies using local, rather than global, species-wide life spans and mortality rates would help to determine the prevalence of life span bias, especially for long-lived species with known life spans. Here, we conducted a field study at two sites in North Carolina to assess potential life span bias between Mercenaria mercenaria and Chione elevata, two long-lived bivalve species that can be aged directly. We compared the ability of directly measured local life spans with that of regional and global life spans to predict live–dead discordance between these two species. The shorter-lived species (C. elevata) was overrepresented in the death assemblage compared with its live abundance, and local life span data largely predicted the amount of live–dead discordance; local life spans predicted 43% to 88% of discordance. Furthermore, the global maximum life span for M. mercenaria resulted in substantial overpredictions of discordance (1.4 to 1.6 times the observed live–dead discordance). The results of this study suggest that life span bias should be considered as a factor affecting proportional abundances of species in death assemblages and that using life span estimates appropriate to the study locality improves predictions of discordance based on life span compared with using global life span estimates.

Taphonomic factors may significantly alter faunal assemblages at varying scales. An exceptional record of late Holocene (<4000 yr old) mammal faunas establishes a firm baseline to investigate the effects of scale on taphonomy. Our sample contains 73 sites within four contiguous states (North Dakota, South Dakota, Iowa, and Illinois, USA) that transect a strong modern and late Holocene environmental gradient, the prairie–forest ecotone. We performed detrended correspondence (DCA) and non-metric multidimensional scaling (NMDS) analyses. Both DCA and NMDS analyses of the data sets produced virtually the same results, and both failed to reveal the known ecological gradient within each state. However, both DCA and NMDS analyses of the unfiltered multistate data set across the entire gradient clearly reflect an environmental, rather than taphonomic, signal. DCA tended to provide better separation of some clusters than did NMDS in most of the analyses. We conclude that a robust mammal data set collected across a strong environmental gradient will document species turnover without the removal of taphonomic factors. In other words, taphonomy exhibits varying scale-dependent effects.