Abundance–diversity relationship as a unique signature of temporal scaling in the fossil record

Species diversity increases with the temporal grain of samples according to the species-time relationship (STR), impacting palaeoecological analyses because the temporal grain (time averaging) of fossil assemblages varies by several orders of magnitude. We predict a positive relation between total abundance and sample size-independent diversity (ADR) in fossil assemblages because an increase in time averaging, determined by a decreasing sediment accumulation, should increase abundance and depress species dominance. We demonstrate that, in contrast to negative ADR of non-averaged living assemblages, the ADR of Holocene fossil assemblages is positive, unconditionally or when conditioned on the energy availability gradient. However, the positive fossil ADR disappears when conditioned on sediment accumulation, demonstrating that ADR is a signature of diversity scaling induced by variable time averaging. Conditioning ADR on sediment accumulation can identify and remove the scaling effect caused by time averaging, providing an avenue for unbiased biodiversity comparisons across space and time.The variability in time averaging pushes the abundance-diversity relationship (using diversity estimates that are independent of sample size) of fossil assemblages towards positive values owing to the species-time relationship. The positive abundance-diversity relationship in the fossil record is thus a distinct signature of diversity scaling induced by variable time averaging. In the fossil record, the scaling effect can be separated from the ecological drivers of the abundance-diversity relationship by conditioning on the sediment accumulation rate.image