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.

Bias in Using an Age–Length Key to Estimate Age-Frequency Distributions

1978 ◽  
Vol 35 (2) ◽  
pp. 184-189 ◽  
Author(s):  
S. J. Westrheim ◽  
W. E. Ricker
Keyword(s):  
Frequency Distribution ◽  
Age Distribution ◽  
Length Distribution ◽  
Fish Population ◽  
Systematic Bias ◽  
Parental Age ◽  
Frequency Distributions ◽  
Class Strength ◽  
Key Words Age ◽  
Age Frequency Distribution

Consider two representative samples of fish taken in different years from the same fish population, this being a population in which year-class strength varies. For the "parental" sample the length and age of the fish are determined and are used to construct an "age–length key," the fractions of the fish in each (short) length interval that are of each age. For the "filial" sample only the length is measured, and the parental age–length key is used to compute the corresponding age distribution. Trials show that the age–length key will reproduce the age-frequency distribution of the filial sample without systematic bias only if there is no overlap in length between successive ages. Where there is much overlap, the age–length key will compute from the filial length-frequency distribution approximately the parental age distribution. Additional bias arises if the rate of growth if a year-class is affected by its abundance, or if the survival rate in the population changes. The length of the fish present in any given part of a population's range can vary with environmental factors such as depth of the water; nevertheless, a sample taken in any part of that range can be used to compute age from the length distribution of a sample taken at the same time in any other part of the range, without systematic bias. But this of course is not likely to be true of samples taken from different populations of the species. Key words: age–length key, bias, Pacific ocean perch, Sebastes alutus

The Climatic Significance of the Hosterman’s Pit Local Fauna, Centre County, Pennsylvania

1967 ◽  
Vol 32 (2) ◽  
pp. 231-232 ◽  
Author(s):  
John E. Guilday
Keyword(s):  
Local Fauna ◽  
Radiocarbon Dates ◽  
Mammal Fauna ◽  
Central Pennsylvania

AbstractThe change from a boreal to a temperate mammal fauna in central Pennsylvania is believed bracketed by radiocarbon dates associated with two cave faunas at from ca. 9300 to 7290 B.C.

Live, dead, and fossil mollusks in Florida freshwater springs and spring-fed rivers: Taphonomic pathways and the formation of multisourced, time-averaged death assemblages

Paleobiology ◽  
2020 ◽  
Vol 46 (3) ◽  
pp. 356-378
Author(s):  
Kristopher M. Kusnerik ◽  
Guy H. Means ◽  
Roger W. Portell ◽  
Mark Brenner ◽  
Quan Hua ◽  
...  
Keyword(s):  
Complex Mixture ◽  
Freshwater Ecosystems ◽  
Time Averaging ◽  
Multiple Sources ◽  
Near Surface ◽  
Radiocarbon Dates ◽  
Freshwater Gastropods ◽  
Melanoides Tuberculata ◽  
Death Assemblages

AbstractTaphonomic processes are informative about the magnitude and timing of paleoecological changes but remain poorly understood with respect to freshwater invertebrates in spring-fed rivers and streams. We compared taphonomic alteration among freshwater gastropods in live, dead (surficial shell accumulations), and fossil (late Pleistocene–early Holocene in situ sediments) assemblages from two Florida spring-fed systems, the Wakulla and Silver/Ocklawaha Rivers. We assessed taphonomy of two gastropod species: the native Elimia floridensis (n = 2504) and introduced Melanoides tuberculata (n = 168). We quantified seven taphonomic attributes (aperture condition, color, fragmentation, abrasion, juvenile spire condition, dissolution, and exterior luster) and combined those attributes into a total taphonomic score (TT). Fossil E. floridensis specimens exhibited the greatest degradation (highest TT scores), whereas live specimens of both species were least degraded. Specimens of E. floridensis from death assemblages were less altered than fossil specimens of the same species. Within death assemblages, specimens of M. tuberculata were significantly less altered than specimens of E. floridensis, but highly degraded specimens dominated in both species. Radiocarbon dates on fossils clustered between 9792 and 7087 cal BP, whereas death assemblage ages ranged from 10,692 to 1173 cal BP. Possible explanations for the observed taphonomic patterns include: (1) rapid taphonomic shell alteration, (2) prolonged near-surface exposure to moderate alteration rates, and/or (3) introduction of reworked fossil shells into surficial assemblages. Combined radiocarbon dates and taphonomic analyses suggest that all these processes may have played a role in death assemblage formation. In these fluvial settings, shell accumulations develop as a complex mixture of specimens derived from multiple sources and characterized by multimillennial time-averaging. These findings suggest that, when available, fossil assemblages may be more appropriate than death assemblages for assessing preindustrial faunal associations and recent anthropogenic changes in freshwater ecosystems.

scholarly journals Shape Analysis of Cumulative Probability Density Function of Radiocarbon Dates Set in the Study of Climate Change in the Late Glacial and Holocene

Radiocarbon ◽  
2004 ◽  
Vol 46 (2) ◽  
pp. 733-744 ◽  
Author(s):  
Danuta J Michczyńska ◽  
Anna Pazdur
Keyword(s):  
Organic Matter ◽  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Late Glacial ◽  
Cumulative Probability ◽  
Large Set ◽  
Radiocarbon Dates ◽  
Frequency Distributions ◽  
The Holocene

We report on a statistical analysis of a large set of radiocarbon dates for reconstruction of paleoclimate. Probability density functions were constructed by summing the probability distributions of individual 14C dates. Our analysis was based on 2 assumptions: 1) The amount of organic matter in sediments depends on paleogeographical conditions; 2) The number of 14C-dated samples is proportional to the amount of organic matter deposited in sediments in the examined time intervals. We quantified how many dates are required to give statistically reliable results. As an example, 785 peat dates from Poland were selected. The dates encompassed the Holocene and Late Glacial period. All dates came from the Gliwice Radiocarbon Laboratory. Results were compared with other paleoenvironmental records. Detailed analysis of the frequency distributions showed that preferential sampling plays an important part in the shape determination. The general rule to take samples from locations where visible changes of sedimentation are apparent (e.g. from the top and the bottom of the peat layer) results in narrow peaks in the probability density function near the limits of the Holocene subdivision.

scholarly journals Statistical inference of prehistoric demography from frequency distributions of radiocarbon dates: a review and a guide for the perplexed

2021 ◽  
Author(s):  
Enrico R. Crema
Keyword(s):  
Frequency Data ◽  
Statistical Nature ◽  
Radiocarbon Dates ◽  
Frequency Distributions ◽  
Practical Applications ◽  
Time Frequency ◽  
Comparative Demography ◽  
Frequency Changes ◽  
Past Population

The last decade saw a rapid increase in the number of applications where time-frequency changes of radiocarbon dates have been used as a proxy for inferring past population dynamics. Although its simple and universal premise is appealing and undoubtedly offers some unique opportunities for research on long-term comparative demography, practical applications are far from trivial and riddled by challenges. Here I review: 1) the most common criticisms concerning the nature of radiocarbon time-frequency data as a demographic proxy; 2) the statistical nature of the problem; and 3) three classes of inferential approaches proposed so far in the literature.

scholarly journals Influence and Impact of Data Averaging and Temporal Resolution on the Assessment of Energetic, Economic and Technical Issues of Hybrid Photovoltaic-Battery Systems

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 354 ◽  
Author(s):  
Alessandro Burgio ◽  
Daniele Menniti ◽  
Nicola Sorrentino ◽  
Anna Pinnarelli ◽  
Zbigniew Leonowicz
Keyword(s):  
Temporal Resolution ◽  
Storage System ◽  
Time Estimation ◽  
Life Time ◽  
Solar Irradiation ◽  
Utilization Rate ◽  
Time Averaging ◽  
Load Profile ◽  
Electricity Bill ◽  
The Impact

The temporal resolution of the demand and generation profiles may have a significant impact on the estimation of self-sufficiency and self-consumption for consumers and prosumers. As an example, measuring the load profile, with a low temporal resolution, may lead to the under-estimation of energy consumption, while measuring solar irradiation with a low temporal resolution may lead to the over-estimation of on-site energy generation. Storage systems may reduce errors due to the lower temporal resolution by 8–10 times or even more, depending on the capacity of the batteries. Besides self-generation and self-consumption, there are other indicators that can be influenced by temporal resolution that deserve to be investigated. This is a detailed study of the influence of temporal resolution and the time averaging on a hybrid photovoltaic-battery system; this study encompasses both economic and technical aspects, from the calculation of savings on the electricity bill to the estimation of the equivalent cycles of battery storage system. To this end, the three-minute load profile of a real case study is used to obtain other three load profiles with temporal resolution equal to 15, 30, and 60 min via data averaging. Therefore, the authors analyze the influence and the impact of temporal resolution and data averaging in terms of: The size of the photovoltaic generator and the capacity of the storage system; the savings in the electricity bill and the balance between costs and savings; the peak values and the average values of power flows during high generation and low generation; the profile of the storage system over the year; the utilization rate of the storage system and the rated power of the electronic converter that regulates the charge and the discharge; the profile of the state of charge of the storage system and the life-time estimation of batteries through the calculation of the equivalent number of cycles.

Taking advantage of time-averaging

Paleobiology ◽  
1999 ◽  
Vol 25 (2) ◽  
pp. 226-238 ◽  
Author(s):  
Thomas Olszewski
Keyword(s):  
Temporal Resolution ◽  
Full Range ◽  
Exponential Model ◽  
Published Data ◽  
Time Interval ◽  
Time Averaging ◽  
Short Term ◽  
Constant Rate ◽  
Rapid Destruction

AbstractOne of the major obstacles in dealing with any form of data derived from fossils is the effects of time-averaging, which are the result of mixing the remains of organisms that did not live contemporaneously. Although this process results in loss of temporal resolution, it also serves to filter out short-term variations. Temporal resolution of a collection depends not only on the range of fossil ages, but also on their frequency distribution. Previous studies of marine molluscs indicate that most shells in an accumulation are relatively young. Such a distribution of shell ages can be fit by an exponential curve (assuming both a constant probability of shell loss and a constant rate of shell addition), which implies that 90% of the shells were added during the last 50% of the time interval represented by the collection. That is to say, differences between two collections can be discerned even if they overlap 50% in time, because the proportion of shells with shared ages is only 10%. Applying the exponential model to previously published data suggests that long-term rates of destruction are controlled by how frequently shells from the taphonomically active zone are re-exposed to rapid destruction. To take advantage of the “noise-filtering” property of time-averaging, samples need to be large enough to catch the full range of environmental variation recorded by an accumulation. A simple probability formula indicates that samples of easily achievable size can give satisfactory time-averaged results depending on the level of confidence and sampling density defined by the researcher.

Developmental origins of normal and anomalous random right-left asymmetry: lateral inhibition versus developmental error in a threshold trait

2012 ◽  
Vol 81 (2) ◽  
pp. 111-124 ◽  
Author(s):  
A. Richard Palmer
Keyword(s):  
Lateral Inhibition ◽  
Stochastic Variation ◽  
Frequency Distributions ◽  
Developmental Variation ◽  
Threshold Trait ◽  
Models Of Development ◽  
Adaptive Explanation ◽  
Relevant Variables ◽  
Alternative Hypotheses ◽  
The Asymmetry

Dramatic examples of right-left asymmetry often inspire adaptive explanations, simply because it is hard to imagine how such forms could not be functionally significant. But are conspicuous morphological asymmetries necessarily adaptive? Surprisingly, in some species where direction of asymmetry is random, asymmetry in bilaterally paired traits may arise as a developmental error in a threshold trait. When cases of asymmetry are rare within a species, they are easily recognized as developmental errors. However, as asymmetrical individuals become more common, or if the asymmetry is in a signaling trait, the temptation to advance an adaptive explanation grows, particularly if the asymmetry is not clearly maladaptive. Several models of the ontogeny of asymmetry are described for both normal and anomalous random asymmetry of bilaterally paired traits. In the absence of selection, each model predicts different expected frequencies of symmetrical and asymmetrical individuals within a species, therefore such frequency distributions can effectively test for different models of development. In normal random asymmetries – where conspicuously asymmetrical individuals predominate – lateral inhibition of one side after the other has transformed appears to be an essential step in development. In anomalous random asymmetries – where conspicuously asymmetrical individuals are relatively rare – no lateral inhibition is required. Other potentially relevant variables include: purely stochastic variation in morphogen levels, useinduced asymmetry, and local (each side independent) versus central (e.g., hormonal) signaling. Examples of normal and anomalous random asymmetries are reviewed for several animal groups. A closer examination of the spectacular forelimb asymmetry in empidid dance flies raises doubts about claims that the asymmetry – both its occurrence and its direction – is adaptive, even though enlargement of the forelimbs likely is. Additional studies are required to conclude that this asymmetry is truly adaptive, as opposed to the outcome of random developmental variation in a threshold trait. This dance-fly leg asymmetry illustrates nicely how alternative hypotheses need to be considered before interpreting such variation as adaptive, even in a signaling trait.

Inferring skeletal production from time-averaged assemblages: skeletal loss pulls the timing of production pulses towards the modern period

Paleobiology ◽  
2015 ◽  
Vol 42 (1) ◽  
pp. 54-76 ◽  
Author(s):  
Adam Tomašových ◽  
Susan M. Kidwell ◽  
Rina Foygel Barber
Keyword(s):  
Sea Level ◽  
Historical Ecology ◽  
Single Pulse ◽  
Bimodal Distribution ◽  
Time Averaging ◽  
Frequency Distributions ◽  
Age Cohorts ◽  
Conservation Paleobiology ◽  
History Of ◽  
Rate Of Decline

AbstractAge-frequency distributions of dead skeletal material on the landscape or seabed—information on the time that has elapsed since the death of individuals—provide decadal- to millennial-scale perspectives both on the history of production and on the processes that lead to skeletal disintegration and burial. So far, however, models quantifying the dynamics of skeletal loss have assumed that skeletal production is constant during time-averaged accumulation. Here, to improve inferences in conservation paleobiology and historical ecology, we evaluate the joint effects of temporally variable production and skeletal loss on postmortem age-frequency distributions (AFDs) to determine how to detect fluctuations in production over the recent past from AFDs. We show that, relative to the true timing of past production pulses, the modes of AFDs will be shifted to younger age cohorts, causing the true age of past pulses to be underestimated. This shift in the apparent timing of a past pulse in production will be stronger where loss rates are high and/or the rate of decline in production is slow; also, a single pulse coupled with a declining loss rate can, under some circumstances, generate a bimodal distribution. We apply these models to death assemblages of the bivalveNuculana taphriafrom the Southern California continental shelf, finding that: (1) an onshore-offshore gradient in time averaging is dominated by a gradient in the timing of production, reflecting the tracking of shallow-water habitats under a sea-level rise, rather than by a gradient in disintegration and sequestration rates, which remain constant with water depth; and (2) loss-corrected model-based estimates of the timing of past production are in good agreement with likely past changes in local production based on an independent sea-level curve.

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.

Sign in / Sign up

Export Citation Format

Share Document