Fidelity of variation in species composition and diversity partitioning by death assemblages: time-averaging transfers diversity from beta to alpha levels

Paleobiology ◽  
2009 ◽  
Vol 35 (1) ◽  
pp. 94-118 ◽  
Author(s):  
Adam Tomašových ◽  
Susan M. Kidwell
Keyword(s):  
Species Composition ◽  
Temporal Variation ◽  
Temporal Resolution ◽  
Beta Diversity ◽  
Fossil Record ◽  
Time Averaging ◽  
Data Sets ◽  
Diversity Partitioning ◽  
Preservation Potential ◽  
Death Assemblages

Despite extensive paleoecological analyses of spatial and temporal turnover in species composition, the fidelity with which time-averaged death assemblages capture variation in species composition and diversity partitioning of living communities remains unexplored. Do death assemblages vary in composition between sites to a lesser degree than do living assemblages, as would be predicted from time-averaging? And is the higher number of species observed in death relative to living assemblages reduced with increasing spatial scale? We quantify the preservation of spatial and temporal variation in species composition using 11 regional data sets based on samples of living molluscan communities and their co-occurring time-averaged death assemblages. (1) Compositional dissimilarities among living assemblages (LA) within data sets are significantly positively rank-correlated to dissimilarities among counterpart pairs of death assemblages (DA), demonstrating that pairwise dissimilarity within a study area has a good preservation potential in the fossil record. Dissimilarity indices that downplay the abundance of dominant species return the highest live-dead agreement of variation in species composition. (2) The average variation in species composition (average dissimilarity) is consistently smaller in DAs than in LAs (9 of 11 data sets). This damping of variation might arise from DAs generally having a larger sample size, but the reduction by ∼10–20% mostly persists even in size-standardized analyses (4 to 7 of 11 data sets, depending on metric). Beta diversity expressed by the number of compositionally distinct communities is also significantly reduced in death assemblages in size-standardized analyses (by ∼25%). This damping of variation and reduction in beta diversity is in accord with the loss of temporal resolution expected from time-averaging, without invoking taphonomic bias (from differential preservation or postmortem transportation) or sample-size effects. The loss of temporal resolution should directly reduce temporal variation, and assuming time-for-space substitution owing to random walk within one habitat and/or temporal habitat shifting, it also decreases spatial variation in species composition. (3) DAs are more diverse than LAs at the alpha scale, but the difference is reduced at gamma scales because partitioning of alpha and beta components differs significantly between LAs and DAs. This indicates that the effects of time-averaging are reduced with increasing spatial scale. Thus, overall, time-averaged molluscan DAs do capture variation among samples of the living assemblage, but they tend to damp the magnitude of variation, making them a conservative means of inferring change over time or variation among regions in species composition and diversity. Rates of temporal and spatial species turnover documented in the fossil record are thus expected to be depressed relative to the turnover rates that are predicted by models of community dynamics, which assume higher temporal resolution. Finally, the capture by DAs of underlying variation in the LA implies little variation in the net preservation potential of death assemblages across environments, despite the different taphonomic pathways suggested by taphofacies studies.

scholarly journals Beta Diversity Partitioning and Drivers of Variations in Fish Assemblages in a Headwater Stream: Lijiang River, China

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 680 ◽  
Author(s):  
Liangliang Huang ◽  
Jian Huang ◽  
Zhiqiang Wu ◽  
Yuanmin Mo ◽  
Qi Zou ◽  
...  
Keyword(s):  
Species Composition ◽  
Beta Diversity ◽  
Fish Assemblages ◽  
Headwater Streams ◽  
Species Turnover ◽  
Diversity Partitioning ◽  
Spatial Variables ◽  
Lijiang River ◽  
Abiotic Variables ◽  
Hydrological Variables

Beta diversity partitioning has currently received much attention in research of fish assemblages. However, the main drivers, especially the contribution of spatial and hydrological variables for species composition and beta diversity of fish assemblages are less well studied. To link species composition to multiple abiotic variables (i.e., local environmental variables, hydrological variables, and spatial variables), the relative roles of abiotic variables in shaping fish species composition and beta diversity (i.e., overall turnover, replacement, and nestedness) were investigated in the upstream Lijiang River. Species composition showed significant correlations with environmental, hydrological, and spatial variables, and variation partitioning revealed that the local environmental and spatial variables outperformed hydrological variables, and especially abiotic variables explained a substantial part of the variation in the fish composition (43.2%). The overall species turnover was driven mostly by replacement (87.9% and 93.7% for Sørensen and Jaccard indices, respectively) rather than nestedness. Mantel tests indicated that the overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU) were significantly related to hydrological, environmental, and spatial heterogeneity, whereas nestedness (ßSNE or ßJNE) was insignificantly correlated with abiotic variables (P > 0.05). Moreover, the pure effect of spatial variables on overall species turnover (ßSOR and ßJAC) and replacement (ßSIM and ßJTU), and the pure effect of hydrological variables on replacement (ßSIM and ßJTU), were not important (P > 0.05). Our findings demonstrated the relative importance of interactions among environmental, hydrological, and spatial variables in structuring fish assemblages in headwater streams; these fish assemblages tend to be compositionally distinct, rather than nested derivatives of one another. Our results, therefore, indicate that maintaining natural flow dynamics and habitat continuity are of vital importance for conservation of fish assemblages and diversity in headwater streams.

Preservation of spatial and environmental gradients by death assemblages

Paleobiology ◽  
2009 ◽  
Vol 35 (1) ◽  
pp. 119-145 ◽  
Author(s):  
Adam Tomašových ◽  
Susan M. Kidwell
Keyword(s):  
Community Structure ◽  
Community Composition ◽  
Environmental Gradients ◽  
Compositional Variation ◽  
Time Averaging ◽  
Data Sets ◽  
Square Root ◽  
Spatial Gradients ◽  
Death Assemblages ◽  
The Impact

Although only a few studies have explicitly evaluated live-dead agreement of species and community responses to environmental and spatial gradients, paleoecological analyses implicitly assume that death assemblages capture these gradients accurately. We use nine data sets from modern, relatively undisturbed coastal study areas to evaluate how the response of living molluscan assemblages to environmental gradients (water depth and seafloor type; “environmental component” of a gradient) and geographic separation (“spatial component”) is captured by their death assemblages. We find that:1. Living assemblages vary in composition either in response to environmental gradients alone (consistent with a species-sorting model) or in response to a combination of environmental and spatial gradients (mass-effect model). None of the living assemblages support the neutral model (or the patch-dynamic model), in which variation in species abundance is related to the spatial configuration of stations alone. These findings also support assumptions that mollusk species consistently differ in responses to environmental gradients, and suggest that in the absence of postmortem bias, environmental gradients might be accurately captured by variation in species composition among death assemblages. Death assemblages do in fact respond uniquely to environmental gradients, and show a stronger response when abundances are square-root transformed to downplay the impact of numerically abundant species and increase the effect of rare species.2. Species' niche positions (position of maximum abundance) along bathymetric and sedimentary gradients in death assemblages show significantly positive rank correlations to species positions in living assemblages in seven of nine data sets (both square-root-transformed and presence-absence data).3. The proportion of compositional variation explained by environmental gradients in death assemblages is similar to that of counterpart living assemblages. Death assemblages thus show the same ability to capture environmental gradients as do living assemblages. In some instances compositional dissimilarities in death assemblages show higher rank correlation with spatial distances than with environmental gradients, but spatial structure in community composition is mainly driven by spatially structured environmental gradients.4. Death assemblages correctly identify the dominance of niche metacommunity models in mollusk communities, as revealed by counterpart living assemblages. This analysis of the environmental resolution of death assemblages thus supports fine-scale niche and paleoenvironmental analyses using molluscan fossil records. In spite of taphonomic processes and time-averaging effects that modify community composition, death assemblages largely capture the response of living communities to environmental gradients, partly because of redundancy in community structure that is inherently associated with multispecies assemblages. The molluscan data sets show some degree of redundancy as evidenced by the presence of at least two mutually exclusive subsets of species that replicate the community structure, and simple simulations show that between-sample relationships can be preserved and remain significant even when a large proportion of species is randomly removed from data sets.

The taphonomic clock in fish otoliths

Paleobiology ◽  
2021 ◽  
pp. 1-17
Author(s):  
Konstantina Agiadi ◽  
Michele Azzarone ◽  
Quan Hua ◽  
Darrell S. Kaufman ◽  
Danae Thivaiou ◽  
...  
Keyword(s):  
Fossil Record ◽  
Radiocarbon Dating ◽  
Pelagic Fish ◽  
Time Averaging ◽  
Target Species ◽  
Local Conditions ◽  
Preservation Potential ◽  
Species Population ◽  
Clock Hypothesis ◽  
Fish Otoliths

Abstract Paleobiological and paleoecological interpretations rely on constraining the temporal resolution of the fossil record. The taphonomic clock, that is, a correlation between the alteration of skeletal material and its age, is an approach for quantifying time-averaging scales. We test the taphonomic clock hypothesis for marine demersal and pelagic fish otoliths from a 10–40 m depth transect on the Mediterranean siliciclastic Israeli shelf by radiocarbon dating and taphonomic scoring. Otolith ages span the last ~8000 yr, with considerable variation in median and range along the transect. Severely altered otoliths, contrary to pristine otoliths, are likely to be older than 1000 yr. For pelagic fish otoliths, at 30 m depth, taphonomic degradation correlates positively with postmortem age. In contrast, no correlation occurs for demersal fishes at 10 and 30 m depth, mostly because of the paucity of very young pristine (<150 yr) otoliths, possibly due to a drop in production over the last few centuries. Contrary to molluscan and brachiopod shells, young otoliths at these depths are little affected and do not show a broad spectrum of taphonomic damage, because those that derive from predation are excreted in calcium- and phosphate-rich feces forming an insoluble crystallic matrix that increases their preservation potential. At 40 m depth, all dated otoliths are very young but rather damaged because of locally chemically aggressive sediments, thus showing no correlation between taphonomic grade and postmortem age. Our results show that local conditions and the target species population dynamics must be considered when testing the taphonomic clock hypothesis.

The preservational fidelity of evenness in molluscan death assemblages

Paleobiology ◽  
2007 ◽  
Vol 33 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Thomas D. Olszewski ◽  
Susan M. Kidwell
Keyword(s):  
Environmental Gradient ◽  
Time Averaging ◽  
Data Sets ◽  
Sufficient Time ◽  
Soft Bottom ◽  
Rapid Loss ◽  
Fine Mesh ◽  
Death Assemblages ◽  
Species Abundances ◽  
Depositional Setting

The richness (number of species) and evenness (uniformity of species abundances) of death assemblages can differ from corresponding living communities due to processes such as between-habitat transport, environmental condensation, and differential taphonomic destruction. Analysis of 132 single-census live-dead comparisons of benthic molluscs from a variety of soft-bottom marine settings indicates that on average evenness does not differ greatly between live and dead assemblages, regardless of the particular depositional setting or grain size of associated sediment. However, individual death assemblages can deviate quite substantially from their corresponding living assemblages, especially if processed using a fine mesh. In addition, death assemblages collected using sieves with 2 mm mesh or coarser showed consistently and significantly greater evenness than corresponding living assemblages. These results are encouraging for broad-scale assessments of evenness in the fossil record based on the comparison of average values (rather than for individual assemblages) and where trends in evenness are the aim of the study.Our live-dead comparisons of richness sample-size corrected by rarefaction revealed that death assemblages were on average ~1.45 times richer than the corresponding living assemblages regardless of rarefied size. In 63.6% of death assemblages both dead richness and dead evenness were greater than live, suggesting sufficient time-averaging to catch significant random or directional changes in the living community and/or introduction of individuals from outside the sampled habitat. In 12.9% of collections both dead richness and dead evenness were less than live, suggesting either rapid loss of dead shells so that dead diversity is depressed below the local living community or selective loss of taphonomically vulnerable taxa. In 18.2% of data sets dead richness was elevated but dead evenness was depressed relative to live: these are interpreted to reflect the addition of low-evenness allochthonous material. The remaining 4.5% of data sets had elevated dead evenness but depressed dead richness, suggesting that live and dead in this case may not be closely related.In seven available time series, temporal volatility in living communities over 6–24 months was considerable but could not account for observed (mostly higher) evenness values in corresponding death assemblages, whose evenness and composition were quite stable in the few examined studies. A densely sampled spatial transect shows that changes in living-assemblage evenness along an environmental gradient were preserved in the corresponding death assemblages, although dead evenness at any location on the gradient was substantially higher than living evenness.

Processes of time-averaging in the terrestrial vertebrate record

1993 ◽  
Vol 6 ◽  
pp. 102-124 ◽  
Author(s):  
Russell W. Graham
Keyword(s):  
Temporal Resolution ◽  
Fossil Record ◽  
Time Averaging ◽  
The Past ◽  
Terrestrial Vertebrate

The terrestrial vertebrate fossil record provides a window into the past evolution of taxa, communities, and ecosystems. It can also be used to reconstruct ancient environments, climates, and landscapes. Vertebrate fossils can document the evolution of humans and their interactions with fauna and environments. However, before the maximum potential of this record can be realized, it is essential to know the extent of temporal resolution, or time-averaging, represented by fossil samples.

Kyiv park "Nivki" and "Teremki" forests and ecological analysis of their habitats

2014 ◽  
Vol 25 (3-4) ◽  
pp. 53-68
Author(s):  
I. V. Goncharenko ◽  
H. M. Holyk
Keyword(s):  
Standard Deviation ◽  
Species Composition ◽  
Human Impact ◽  
Soil Nitrogen ◽  
Beta Diversity ◽  
Plant Cover ◽  
Alpha Diversity ◽  
Light Regime ◽  
Individual Species ◽  
Anthropogenic Pressure

Cenotic diversity and leading ecological factors of its floristic differentiation were studied on an example of two areas – Kyiv parks "Nivki" and "Teremki". It is shown that in megalopolis the Galeobdoloni-Carpinetum impatientosum parviflorae subassociation is formed under anthropogenic pressure on the typical ecotope of near-Dnieper hornbeam oak forests on fresh gray-forest soils. The degree of anthropogenic transformation of cenofloras can be estimated by the number of species of Robinietea and Galio-Urticetea classes, as well as neophytes and cultivars. Phytoindication for hemeroby index may be also used in calculation. We propose the modified index of biotic dispersion (normalized by alpha-diversity) for the estimation of ecophytocenotic range (beta-diversity) of releves series. We found that alpha-diversity initially increases (due to the invasion of antropophytes) at low level of antropogenic pressure, then it decreases (due to the loss of aboriginal species) secondarily with increasing of human impact. Also we found that beta-diversity (differential diversity) decreases, increasing homogeneity of plant cover, under the influence of anthropogenic factor. Vegetation classification was completed by a new original method of cluster analysis, designated as DRSA («distance-ranked sorting assembling»). The classification quality is suggested to be validated on the "seriation" diagram, which is а distance matrix between objects with gradient filling. Dark diagonal blocks confirm clusters’ density (intracluster compactness), uncolored off-diagonal blocks are evidence in favor of clusters’ isolation (intercluster distinctness). In addition, distinction of clusters (syntaxa) in ordination area suggests their independence. For phytoindication we propose to include only species with more than 10% constancy. Furthermore, for the description of syntaxonomic amplitude we suggest to use 25%-75% interquartile scope instead of mean and standard deviation. It is shown that comparative analysis of syntaxa for each ecofactor is convenient to carry out by using violin (bulb) plots. A new approach to the phytoindication of syntaxa, designated as R-phytoindication, was proposed for our study. In this case, the ecofactor values, calculated for individual releves, are not taken into account, however, the composition of cenoflora with species constancies is used that helps us to minimize for phytoindication the influence of non-typical species. We suggested a syntaxon’s amplitude to be described by more robust statistics: for the optimum of amplitude (central tendency) – by a median (instead of arithmetic mean), and for the range of tolerance – by an interquartile scope (instead of standard deviation). We assesses amplitudes of syntaxa by phytoindication method for moisture (Hd), acidity (Rc), soil nitrogen content (Nt), wetting variability (vHd), light regime (Lc), salt regime (Sl). We revealed no significant differences on these ecofactors among ecotopes of our syntaxa, that proved the variant syntaxonomic rank for all syntaxa. We found that the core of species composition of our phytocenoses consists of plants with moderate requirements for moisture, soil nitrogen, light and salt regime. We prove that the leading factor of syntaxonomic differentiation is hidden anthropogenic, which is not subject to direct measurement. But we detect that hidden factor of "human pressure" was correlated with phytoindication parameters (variables) that can be measured "directly" by species composition of plant communities. The most correlated factors were ecofactors of soil nitrogen, wetting variability, light regime and hemeroby. The last one is the most indicative empirically for the assessment of "human impact". We establish that there is a concept of «hemeroby of phytocenosis» (tolerance to human impact), which can be calculated approximately as the mean or the median of hemeroby scores of individual species which are present in it.

TAPHONOMY AND TIME AVERAGING OF MOLLUSCAN DEATH ASSEMBLAGES IN FLORIDA SPRINGS AND RIVERS

2018 ◽  
Author(s):  
Kristopher M. Kusnerik ◽  
◽  
Harley Means ◽  
Roger W. Portell ◽  
Michal Kowalewski
Keyword(s):  
Time Averaging ◽  
Death Assemblages ◽  
Florida Springs

Species composition and spatio-temporal variation of bycatch from mid-water trawlers operating in the Arabian Sea along north-west coast of India

2021 ◽  
Vol 43 ◽  
pp. 101692
Author(s):  
P. Abdul Azeez ◽  
Prathibha Rohit ◽  
Latha Shenoy ◽  
Ashok Kumar Jaiswar ◽  
Mini Raman ◽  
...  
Keyword(s):  
Species Composition ◽  
Temporal Variation ◽  
West Coast ◽  
Arabian Sea ◽  
North West ◽  
West Coast Of India ◽  
Spatio Temporal

Quantitative comparisons and models of time-averaging in bivalve and brachiopod shell accumulations

Paleobiology ◽  
2010 ◽  
Vol 36 (3) ◽  
pp. 428-452 ◽  
Author(s):  
Richard A. Krause ◽  
Susan L. Barbour ◽  
Michał Kowalewski ◽  
Darrell S. Kaufman ◽  
Christopher S. Romanek ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Time Averaging ◽  
Local Fauna ◽  
Stochastic Variation ◽  
Extrinsic Factors ◽  
Radiocarbon Dates ◽  
Frequency Distributions ◽  
Spatial And Temporal Scales ◽  
Deep Site ◽  
Age Frequency Distribution

The variation in time-averaging between different types of marine skeletal accumulations within a depositional system is not well understood. Here we provide quantitative data on the magnitude of time-averaging and the age structure of the sub-fossil record of two species with divergent physical and ecological characteristics, the brachiopodBouchardia roseaand the bivalveSemele casali.Material was collected from two sites on a mixed carbonate-siliciclastic shelf off the coast of Brazil where both species are dominant components of the local fauna.Individual shells (n= 178) were dated using amino acid racemization (aspartic acid) calibrated with 24 AMS radiocarbon dates. Shell ages range from modern to 8118 yearsb.p.for brachiopods, and modern to 4437 years for bivalves. Significant differences in the shape and central tendency of age-frequency distributions are apparent between each sample. Such differences in time-averaging magnitude confirm the assumption that taphonomic processes are subject to stochastic variation at all spatial and temporal scales. Despite these differences, each sample is temporally incomplete at centennial resolution and three of the four samples have similar right-skewed age-frequency distributions. Simulations of temporal completeness indicate that samples of both species from the shallow site are consistent with a more strongly right-skewed and less-complete age-frequency distribution than those from the deep site.We conclude that intrinsic characteristics of each species exert less control on the time-averaging signature of these samples than do extrinsic factors such as variation in rates of sedimentation and taphonomic destruction. This suggests that brachiopod-dominated and bivalve-dominated shell accumulations may be more similar in temporal resolution than previously thought, and that the temporal resolution of multi-taxic shell accumulations may depend more on site-to-site differences than on the intrinsic properties of the constituent organisms.

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