DOI: 10.5061/dryad.8sk4r
title: Data from: Explaining high-diversity death assemblages: undersampling of the living community, out-of-habitat transport, time-averaging of rare taxa, and local extinction

description: Molluscan benthic assemblages provide unique opportunities for
 understanding both spatial and temporal patterns of biodiversity. Species
 richness in the shell remains found at a site (i.e. the death assemblage)
 is typically several times higher than in the counterpart living
 assemblage, reflecting a complex history of settlement, dissemination and
 decomposition post-mortem. We used high-density temporal and spatial
 sampling (&gt;37’000 individuals representing 196 taxa) of a shallow
 (5-8 m) nearshore sandy habitat off the coast of south-east Sardinia
 (Italy, Mediterranean Sea) to study the factors responsible for
 differences in the relative diversity of living and death assemblages. We
 found that death assemblages at all sites were considerably more diverse
 than living communities (1.5-3.5x more dead than living taxa after
 sample-size standardization), with 78% of all taxa solely recovered as
 empty shells, resulting in low live-dead agreement. By carefully filtering
 the raw data and combining them with habitat information extracted from
 the literature, we disentangled the major causes of this discordance and
 quantified their individual effects. Increased dead diversities could not
 be attributed to undersampling of the living community, but instead
 resulted from three phenomena of decreasing importance: the post-mortem,
 out-of-habitat transport of non-indigenous taxa (57% of dead-only taxa
 were allochthonous), the time-averaged presence of rare indigenous taxa
 (40% of dead-only taxa), and the likely local extirpation of a small
 number of species (3% of dead-only taxa). Our approach demonstrates how
 ecological inferences based on death assemblages can be improved by
 restricting analyses to demonstrably indigenous taxa, and highlights how
 mollusc shell remains can be used to provide information over both
 ecological and evolutionary timescales.
description: Data with maximum number
 of bivalve individuals, including unidentified individuals (XNI
 approach)This table provides the
 raw numbers of living and dead specimens of all mollusc taxa that were
 recovered in benthic assemblages, listed separately for all censuses. The
 dataset includes the few dead bivalve and gastropod specimens that could
 not be identified and were thus excluded from all analyses. Individual
 numbers are uncorrected for disarticulated valves of single bivalve
 individuals. As each empty bivalve valve was assumed to represent a unique
 individual ("XNI approach"), this dataset thus provides the
 maximum number of bivalve individuals.Data with maximum number
 of bivalve individuals (XNI approach)This table provides the
 raw numbers of living and dead specimens of all mollusc taxa that were
 recovered in benthic assemblages, listed separately for all censuses.
 Individual numbers are uncorrected for disarticulated valves of single
 bivalve individuals. As each empty bivalve valve was assumed to represent
 a unique individual ("XNI approach"), this dataset thus provides
 the maximum number of bivalve individuals.Data with minimum number
 of bivalve individuals (MNI approach)This table provides the
 numbers of living and dead specimens of all mollusc taxa that were
 recovered in benthic assemblages, listed separately for all censuses.
 Individual numbers are corrected for disarticulated valves of single
 bivalve individuals by assuming that both empty valves of all dead bivalve
 individuals were present in a sample ("the MNI approach"). This
 dataset thus provides the minimum number of bivalve
 individuals.Data with corrected
 number of bivalve individuals (sampling domain 3x size of observed
 collections)This table provides the
 numbers of living and dead individuals of all mollusc taxa that were
 recovered in benthic assemblages, listed separately for all censuses.
 Individual numbers are corrected for disarticulated valves of single
 bivalve individuals by assuming sampling domains three times the size of
 an observed collection. This dataset was used for all analyses presented
 in the manuscript.