The paleoecological significance of diversity: The effect of time averaging and differential preservation on macroinvertebrate species richness in death assemblages

Abstract

The effect of time averaging on species richness of the preservable component (animals with preservable hard parts) of living benthic communities was investgated using long-term (24–30 mo) data sets obtained by recurrent sampling in estuarine and euhaline (30–40 ppt) habitats. About 20–40% of all living species collected were preservable. Species richness of the living community increased with salinity and water depth. Cumulative species richness increased with increasing duration of study. The percentage of preservable species, however, declined with increasing depth. As many preservble species were collected over time in some physically variable estuarine habitats as were collected in the physically less variable, euhaline habitats. Changing environmental factors allowed different species to inhabit these estuarine areas as time passed, whereas species richness was usually higher in euhaline habitats at any particular time. Hence, species richness in the death assemblages may be as high in some physically variable, estuarine habitats as in more invariant euhaline habitats. The species composition of the preservable component of the living community was more persistent than the nonpreservable component. That is, on the average, species additions or replacements occurred more frequently in the nonpreservable component. This increased persistence of the preservable component, however, could not offset the inherently more rapid temporal changes in faunal composition that occurred in physically variable habitats. Therefore, the classic ecologic relationship between increased species richness and reduced environmental variability may not be preserved. Additional evidences must be used to distinguish between species-rich assemblages produced by time averaging of noncontemporaneous taxa in environmentally variable habitats and those produced by diversedcommunities in less variable habitats.