Multiple paleoecological controls on the composition of marine fossil assemblages from the Frasnian (Late Devonian) of Virginia, with a comparison of ordination methods

Paleobiology ◽  
2010 ◽  
Vol 36 (4) ◽  
pp. 573-591 ◽  
Author(s):  
Andrew M. Bush ◽  
Roderic I. Brame
Keyword(s):  
Grain Size ◽  
Species Composition ◽  
Simulated Data ◽  
Ecological Factors ◽  
Detrended Correspondence Analysis ◽  
Late Devonian ◽  
Opportunistic Species ◽  
Disturbance Intensity ◽  
Fossil Assemblages ◽  
Highly Correlated

Ecological ordination can reveal gradients in the species composition of fossil assemblages that can be correlated with paleoenvironmental gradients. Ordinations of simulated data sets suggest that nonmetric multidimensional scaling (NMDS) generally produces less distorted results than detrended correspondence analysis (DCA). We ordinated 113 brachiopod-dominated samples from the Frasnian (Late Devonian) Brallier, Scherr, and lower Foreknobs Formations of southwest Virginia, which represent a range of siliciclastic marine paleoenvironments. A clear environmental signal in the ordination results was obscured by (apparently) opportunistic species that occurred at high abundance in multiple environments; samples dominated by these species aggregated in ordination space regardless of paleoenvironmental provenance. After the opportunist-dominated samples were removed, NMDS revealed a gradient in species composition that was highly correlated with substrate (grain size); a second, orthogonal gradient likely reflects variation in disturbance intensity or frequency within grain-size regimes. Additional environmental or ecological factors, such as oxygenation, may also be related to the gradients. These two gradients, plus the environmental factors that controlled the occurrence of opportunistic species, explain much of the variation in assemblage composition in the fauna. In general, the composition of fossil assemblages is probably influenced by multiple paleoecological and paleoenvironmental factors, but many of these can be decomposed and analyzed.

Vegetation Canopy Coverage Estimation Using Physical Models

2013 ◽  
Vol 726-731 ◽  
pp. 4709-4713
Author(s):  
Lin Jing Zhang ◽  
Hong Zhang Ma ◽  
Zhu Bo Zhou ◽  
Zhong Liang Ren ◽  
Xiao Bo Zhu ◽  
...  
Keyword(s):  
Regression Model ◽  
Simulated Data ◽  
Hyperspectral Data ◽  
Physical Models ◽  
Vegetation Canopy ◽  
Canopy Coverage ◽  
Vegetation Indexes ◽  
Ground Measurement ◽  
Highly Correlated ◽  
Coverage Estimation

Based on the physical models of PROSPECT, SAIL and porosity model, hyperspectral data and canopy coverage data of different combined scenes were simulated. According to the simulated data, we chose four sensitive bands and four sensitive vegetation indexes highly correlated to vegetation canopy coverage, and analyzed the correlation between sensitive bands, sensitive vegetation indexes and canopy coverage. Then we built a regression model of canopy coverage with EVI highly correlated with canopy coverage. At last, we verified this model by experimental data from ground measurement experiment. It shows that there is a high correlation between EVI and canopy coverage and the regression model built by EVI can produce an effective result and the RMSE is less than 0.09.

Differential attrition of molluscan shells in freshwater sediments

1988 ◽  
Vol 25 (1) ◽  
pp. 68-73 ◽  
Author(s):  
Eva Pip
Keyword(s):  
Species Composition ◽  
Energy Conditions ◽  
Small Species ◽  
Freshwater Sediments ◽  
Shell Size ◽  
Attrition Rates ◽  
Delta Marsh ◽  
Fossil Assemblages ◽  
Species Frequencies

Mean seasonal species composition of living molluscan communities was compared with the composition of current dead assemblages in the sediments of three sites located in the Delta Marsh of southern Lake Manitoba. Dead shells were more numerous in vegetated than in bare areas, resulting primarily from the affinities of living molluscs for vegetated areas. Redistribution patterns of empty shells were not significantly different for vegetated and bare areas, as judged from distributions of passively transported land shells in the sediments. Significant differences were observed at all sites between species frequencies in living and corresponding dead assemblages averaged for the season. Proportions of living to dead individuals per unit bottom area indicated higher attrition rates with increasing energy conditions as well as with increasing shell size. Differential attrition may result in overrepresentation of small species in fossil assemblages.

scholarly journals Environmental and ecological factors mediate taxonomic composition and body size of polyplacophoran assemblages along the Peruvian Province

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Christian M. Ibáñez ◽  
Melany Waldisperg ◽  
Felipe I. Torres ◽  
Sergio A. Carrasco ◽  
Javier Sellanes ◽  
...  
Keyword(s):  
Body Size ◽  
Species Composition ◽  
Size Structure ◽  
Environmental Gradients ◽  
Ecological Factors ◽  
Taxonomic Composition ◽  
Latitudinal Gradients ◽  
Size Segregation ◽  
Biogeographic Patterns ◽  
Diversity Gradient

Abstract Intertidal communities’ composition and diversity usually exhibit strong changes in relation to environmental gradients at different biogeographical scales. This study represents the first comprehensive diversity and composition description of polyplacophoran assemblages along the Peruvian Province (SE Pacific, 12°S–39°S), as a model system for ecological latitudinal gradients. A total of 4,775 chitons from 21 species were collected on twelve localities along the Peruvian Province. This sampling allowed us to quantitatively estimate the relative abundance of the species in this assemblage, and to test whether chitons conform to elementary predictions of major biogeographic patterns such as a latitudinal diversity gradient. We found that the species composition supported the division of the province into three ecoregional faunal groups (i.e. Humboldtian, Central Chile, and Araucanian). Though chiton diversity did not follow a clear latitudinal gradient, changes in species composition were dominated by smaller scale variability in salinity and temperature. Body size significantly differed by ecoregions and species, indicating latitudinal size-structure assamblages. In some localities body size ratios differed from a random assemblage, evidencing competition at local scale. Changes in composition between ecoregions influence body size structure, and their overlapping produce vertical size segregation, suggesting that competition coupled with environmental conditions structure these assemblages.

Diversity of subalpine and alpine vegetation of the eastern part of the Nízke Tatry Mts in Slovakia: major types and environmental gradients

Biologia ◽  
2009 ◽  
Vol 64 (5) ◽  
Author(s):  
Lucia Sekulová ◽  
Michal Hájek
Keyword(s):  
Plant Communities ◽  
Environmental Gradients ◽  
Ecological Factors ◽  
Detrended Correspondence Analysis ◽  
Dwarf Shrub ◽  
Soil Reaction ◽  
Data Set ◽  
Entire Data ◽  
Second Gradient ◽  
One Year

AbstractChanges in composition and structure of alpine and subalpine plant communities in relation to ecological factors were analysed in the Nízke Tatry Mts, Slovakia. Species cover values of vascular and non-vascular plants in each vegetation plot were recorded on the nine-degree scale. A data set of 156 relevés of alpine and subalpine vegetation was sampled recently during one year in the eastern part of the Nízke Tatry National Park. The data set was analysed by cluster analysis and Detrended Correspondence Analysis. analyses were carried out on the entire data set, including the subset of short grassland and dwarf-shrub vegetation. Major gradients and clusters were ecologically interpreted using Ellenberg indicator values. In the entire data set, the major gradient in species composition was associated with nutrient availability and the second most important gradient with light. In the case of short grassland and dwarf-shrub vegetation, the gradients were different. The first one was associated with soil reaction and the second gradient was associated with moisture. Clusters proposed by numerical classification reproduced many traditional phytosociological associations, namely Seslerietum distichae, Sphagno capillifolii-Empetretum nigri, Junco trifidi-Callunetum vulgaris, Juncetum trifidi, Dryopterido dilatatae-Pinetum mugo, Luzuletum obscurae, Agrostio pyrenaiceae-Nardetum strictae, while some other associations were less clearly differentiated (communities of the alliances Calamagrostion villosae, Adenostylion alliariae, Trisetion fusci, Cratoneuro filicini-Calthion laetae or Salicion herbaceae). The next clusters included Vaccinium and Festuca supina dominated communities and artificial roadside grasslands sown 50 years ago. Bryophytes and lichens were highly represented among diagnostic species of particular associations. Distribution pattern of particular plant communities was strongly influenced by site position either on northern or southern slope of the mountains.

La végétation forestière du secteur nord-ouest de la vallée du Saint-Laurent, Québec

1988 ◽  
Vol 66 (4) ◽  
pp. 793-804 ◽  
Author(s):  
Claude St-Jacques ◽  
Daniel Gagnon
Keyword(s):  
Acer Saccharum ◽  
Acer Rubrum ◽  
Ecological Factors ◽  
Detrended Correspondence Analysis ◽  
Forest Community ◽  
North West ◽  
The North ◽  
Two Factors ◽  
Community Types ◽  
And Cluster Analysis

The forest vegetation of the north-west section of the St. Lawrence Valley in Quebec was sampled within 68 quadrats. The location of the quadrats was selected by means of a stratified random sampling plan. Ordination (detrended correspondence analysis) and cluster analysis (TWINSPAN) allowed the identification of 11 forest community types. The ecological factors most closely associated with the distribution of these communities are soil drainage and richness. These two factors are strongly related to the types of surface deposits. Communities dominated by Acer saccharum are found on well drained and nutrient-rich moraines. On the contrary, communities dominated by Acer rubrum and the majority of coniferous forests are found on poorly drained and nutrient-poor soils. Two floristically distinct community types, the Fraxinus – Tilia americana forests and the Tsuga canadensis – Acer saccharum forests, are found on poorly drained marine deposits with edaphically identical lower horizons. However, the pH and major cation concentrations of the upper soil horizons are much lower under the cover of the hemlock forests than under the cover of the ash – basswood forests.

scholarly journals A mechanistic empirical approach for the evaluation of the structural capacity and remaining service life of flexible pavements at the network level

2016 ◽  
Vol 43 (8) ◽  
pp. 749-758 ◽  
Author(s):  
Mofreh Saleh
Keyword(s):  
Service Life ◽  
Compressive Strain ◽  
Simulated Data ◽  
Structural Condition ◽  
Remaining Service Life ◽  
Structural Capacity ◽  
Concrete Layer ◽  
Maintenance And Rehabilitation ◽  
Highly Correlated ◽  
Asset Managers

Road asset managers need to utilize reliable indicators for the structural condition and remaining service life at the network level to make rational decisions of the required funding and the optimum strategies for maintenance and rehabilitation. The surface deflection bowls and pavement critical responses were generated by computer simulations for a total of 2880 flexible pavement sections. The normalized area was computed from the deflection bowl data and it was found to be very well correlated with the compressive strain at the top of the subgrade. While the pavement surface curvature and area under pavement profile were highly correlated with the tensile strain at the bottom of the asphalt concrete layer. Thus, these parameters were used to evaluate the remaining service life in rutting and fatigue. Field data showed an excellent match between the trends obtained from the field and computer simulated data.

Estimation of Effective Effort from Catch-at-Age Data

1993 ◽  
Vol 50 (11) ◽  
pp. 2421-2428 ◽  
Author(s):  
J. E. Paloheimo ◽  
Yong Chen
Keyword(s):  
Age Groups ◽  
Simulated Data ◽  
Mortality Rates ◽  
Natural Mortality ◽  
Fishing Mortality ◽  
A Value ◽  
Basic Equations ◽  
Highly Correlated ◽  
High Degree ◽  
Two Age Groups

We present a method for estimating effective efforts or fishing mortality rates based on a linearized version of the catch equation. Catch-at-age for at least two age groups over a series of years is required. The method presupposes a value for natural mortality rate (M). The method is validated using simulated data with an appropriate error structure. The algorithm always converges to a set of effective efforts that are compatible with the known catches. Nevertheless, the solution to the basic equations is not unique although the different solutions are typically highly correlated. If the M assumed by the algorithm is the same as the actual M the iterated effective efforts are typically very close to the true effective efforts or fishing mortality rates. If the assumed M is too high or too low the pattern of effective efforts is still recovered to a high degree of accuracy, typically 0.90 < r < 1.00, even though M may be off by as much as 60%. When data for three or more age groups are available the method is extended to at least squares procedure that takes into account the increasing uncertainty of catches with age.

Grasshopper (Insecta: Orthoptera: Acrididae) assemblages of tallgrass prairie: influences of fire frequency, topography, and vegetation

1988 ◽  
Vol 66 (7) ◽  
pp. 1495-1501 ◽  
Author(s):  
Edward W. Evans
Keyword(s):  
Species Richness ◽  
Species Composition ◽  
Relative Abundance ◽  
Tallgrass Prairie ◽  
Detrended Correspondence Analysis ◽  
Fire Frequency ◽  
Local Species Richness ◽  
Principal Axes ◽  
Local Plant ◽  
Local Species

Grasshopper assemblages were sampled by sweep net in native tallgrass prairie at Konza Prairie, Kansas, in 1982 – 1986 to assess the influences of fire, topography, and vegetation on local species composition. Species composition at 38 sites was analysed by ordination (detrended correspondence analysis). Frequency of fire and topographic location were reflected along the first two principal axes, respectively. Grass-feeding grasshoppers were more numerous than forb- and mixed-feeding grasshoppers throughout the prairie, but forb and mixed feeders became relatively more frequent as fire frequency decreased. Local species richness of grasshoppers was greater on sites burned infrequently than on sites burned annually or biennially, and on upland than on lowland sites. Local species richness was positively correlated with local plant species richness and diversity, reflecting in part that local relative abundance of forb-feeding grasshoppers was positively correlated with local relative abundance of forbs. Collectively these results are consistent in suggesting that through their effects on local plant communities, fire frequency and topography are major factors influencing the composition of local grasshopper assemblages in tallgrass prairie.

scholarly journals Impacts of Human Activities on Tree Species Composition Along the Forest Savanna Boundary in Nigeria

2016 ◽  
Vol 47 (2) ◽  
pp. 115 ◽  
Author(s):  
Christiana Ndidi Egbinola
Keyword(s):  
Species Composition ◽  
Tree Species ◽  
Human Activities ◽  
Detrended Correspondence Analysis ◽  
Floristic Composition ◽  
Forest Species ◽  
Tree Species Composition ◽  
Study Sites ◽  
The Impact ◽  
The Relationship

The study investigated the tree species composition along the forest-savanna boundary in Oyo state of Nigeria with the aim of assessing the impact of human activities on the floristic composition. A transect was placed along the study area and species data was collected from quadrats placed in study plots within different study sites. Detrended Correspondence Analysis (DCA) was used to determine vegetation assemblages, while both correlation and the analysis of variance (ANOVA) were used to show the relationship between species in the different study sites. Results of the DCA revealed three species assemblages, an area with only forest species, another with only savanna species and a third with both forest/savanna species. ANOVA results further revealed that within the forest and savanna assemblages, species in mature and successional sites were alike. The study therefore revealed that human activities’ within the region is leading to the establishment of savanna species and an elimination of forest species.

scholarly journals Grassland communities of Stol mountain (eastern Serbia ): Vegetation and environment al relationships

2013 ◽  
Vol 65 (1) ◽  
pp. 211-227 ◽  
Author(s):  
Svetlana Acic ◽  
U. Silc ◽  
S. Vrbnicanin ◽  
Svjetlana Cupac ◽  
G. Topisirovic ◽  
...  
Keyword(s):  
Species Composition ◽  
Environmental Gradient ◽  
Environmental Gradients ◽  
Detrended Correspondence Analysis ◽  
Ecological Indicator ◽  
Vegetation Types ◽  
Indicator Values ◽  
Grassland Vegetation ◽  
Data Set ◽  
Grassland Communities

The systematic survey of grassland communities was performed on Mt. Stol (eastern Serbia). The main aims of the research were to: (1) determine grassland vegetation types of the researched area; (2) correlate the impacts of the soil and environmental conditions on the occurrence of certain plant communities, and (3) comment on the conservational value of the grasslands in the researched area. The data set included 60 phytosociological relev?s of grasslands recorded between 2001 and 2004. The main environmental gradients of species composition were analyzed by Detrended Correspondence Analysis (DCA). For the ecological interpretation of ordination axes, ecological indicator values were used. Three associations were distinguished: Danthonietum calycinae, Asperulo-Agrostietum vulgaris and Ranunculo bulbosi- Arrhenatheretum elatioris belonging to two alliances and two classes: Chrysopogono-Danthonion - Festuco-Brometea and Arrhenatherion - Molinio-Arrhenatheretea. The results of the DCA support our assumption that the main environmental gradient in the species composition of the grasslands is related to nutrients and moisture. The conservational value of grasslands in the researched area is discussed.

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