10.5061/DRYAD.1225
Tomašových, Adam
University of Chicago
Kidwell, Susan M.
University of Chicago
Data from: Predicting the effects of increasing temporal scale on species
composition, diversity, and rank-abundance distributions
Dryad
dataset
2010
rank abundance
Bivalvia
Holocene
2010-02-04T06:06:04Z
2010-02-04T06:06:04Z
en
https://doi.org/10.1666/08092.1
179396 bytes
1
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Paleoecological analyses that test for spatial or temporal variation in
diversity must consider not only sampling and preservation bias, but also
the effects of temporal scale (i.e., time averaging). The species-time
relationship (STR) describes how species diversity increases with the
elapsed time of observation, but its consequences for assessing the
effects of time averaging on diversity of fossil assemblages remain poorly
explored. Here, we use a neutral, dispersal-limited model of metacommunity
dynamics, with parameters estimated from living assemblages of 31
molluscan datasets, to model the effects of within-habitat time averaging
on the mean composition and multivariate dispersion of assemblages, on
diversity at point (single station) and habitat scales (pooled multiple
stations), and on beta diversity. We hold sample size constant in STRs to
isolate the effects of time averaging from sampling effects. With
increasing within-habitat time-averaging, stochastic switching in the
identity of species in living (dispersal-limited) assemblages (1)
decreases the proportional abundance of abundant species, reducing the
steepness of the rank-abundance distribution, and (2) increases the
proportional richness of rare, temporally-impersistent species that
immigrate from the neutral metacommunity with many rare species. These two
effects together (1) can shift the mean composition away from the
non-averaged (dispersal-limited) assemblages towards averaged assemblages
that are less limited by dispersal, resembling that of the metacommunity,
(2) allow the point and habitat diversity to increase towards
metacommunity diversity under a given sample size (i.e., the diversity in
averaged assemblages is inflated relative to non-averaged assemblages),
and (3) reduce beta diversity because species unique to individual
stations become shared by other stations when limited by a larger but
static species pool. Surprisingly, these changes occur at fixed sample
sizes and can become significant after only a few decades or centuries of
time averaging, and are accomplished without invoking ecological
succession, environmental changes, or selective postmortem preservation.
We find that time averaging results in less inflation of diversity at
habitat than at point scales; paleoecological studies should thus analyze
data at multiple spatial scales, including that of the habitat where
multiple bulk samples have been pooled in order to minimize time averaging
effects. The diversity of assemblages that have accumulated over 1000
years at point and habitat scales is expected to be inflated by an average
of 2.1 and 1.6. This degree of inflation is slightly higher than that
observed in molluscan death assemblages at these same spatial scales (1.8
and 1.3). Thus, neutral metacommunity models provide useful quantitative
constraints on directional but predictable effects of time averaging. They
provide minimal estimates for the rate of increase in diversity with time
averaging because they assume no change in environmental conditions and in
the composition of the metacommunity within the window of averaging.
abundances-S California 1975.xlsProportional abundances of bivalve species
in living and death assemblages sampled on the southern California shelf.
Living assemblages are represented by unpublished data from the 1975
BLM-funded survey conducted by Alan Hancock Foundation, which we have
digitized from rescued print-outs. Death assemblages - data generated by
authors of this paper from unprocessed sieve residues of these same
samples, archived by the Los Angeles County Museum of Natural History.
Mesh size 2 mm. In this study, 2 habitats are represented by sandy muds
and muddy sands ranging from 30 to 90 meters of water depth. All stations
are outside the impact areas of publicly operated wastewater outfalls. See
the excel file with environmental assignment and samples sizes for each
station (sample size can be used to recompute proportional into absolute
abundances).abundances-S California 2003.xlsProportional abundances of
bivalve species in living and death assemblages sampled on the southern
California shelf. Living assemblages are represented by unpublished data
from the 1975 BLM-funded survey conducted by Alan Hancock Foundation,
which we have digitized from rescued print-outs. Death assemblages - data
generated by authors of this paper from unprocessed sieve residues of
these same samples, archived by the Los Angeles County Museum of Natural
History. Mesh size 2 mm. In this study, 2 habitats are represented by
sandy muds and muddy sands ranging from 30 to 90 meters of water depth.
All stations are outside the impact areas of publicly operated wastewater
outfalls. See the excel file with environmental assignment and samples
sizes for each station (sample size can be used to recompute proportional
into absolute abundances).Station information.xlsSample sizes of living
and death assemblages and sedimentologic, geographic and bathymetric
information about the position of individual stations sampled in 1975 and
2003 in the southern California Bight. Stations with muddy sand and sandy
mud were analyzed in this study (four habitats in total).R language source
code.txtThe code in R language used in simulations
southern California