The spatial frequency of climatic conditions affects niche composition and functional diversity of species assemblages: the case of Angiosperms

2019 ◽  
Vol 23 (2) ◽  
pp. 254-264
Author(s):  
Bertrand Fournier ◽  
Héctor Vázquez‐Rivera ◽  
Sylvie Clappe ◽  
Louis Donelle ◽  
Pedro Henrique Pereira Braga ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Functional Diversity ◽  
Climatic Conditions ◽  
Species Assemblages

scholarly journals Historical biogeography of fishes from coastal basins of Maranhão State, northeastern Brazil

2019 ◽  
Vol 17 (2) ◽  
Author(s):  
João Marcelo S. Abreu ◽  
Jack M. Craig ◽  
James S. Albert ◽  
Nivaldo M. Piorski
Keyword(s):  
Fish Species ◽  
Climatic Conditions ◽  
Northeastern Brazil ◽  
Species Assemblages ◽  
Biogeographic History ◽  
Biogeographic Provinces ◽  
Species Pairs ◽  
The World ◽  
History Of ◽  
Coastal Basins

ABSTRACT The Amazonian ichthyofauna is one of the most diverse in the world, yet fishes from the adjacent coastal basins of Maranhão State in Northeastern Brazil remain poorly known. We use phylogeographic, community phylogenetic and phylogenetic beta diversity methods to study the biogeographic history of fishes from the coastal basins of Maranhão State. We report a total of 160 fish species from the basins of the Maranhão region, representing a 93% increase over results of previous studies. All the fish species assemblages from Maranhão are polyphyletic, with only a few putative sister species pairs inhabiting the region. The modern watershed divides among Maranhão basins do not form substantial barriers to dispersal for freshwater fish species, and are more effectively modelled as biogeographic islands than as biogeographic provinces. In combination these results suggest that the Maranhão ichthyofauna was assembled under the influence of several macroevolutionary (extinction, dispersal) and landscape evolution processes, during the Miocene and Pliocene, as well as by the modern ecological characteristics of the region. The results indicate that the distinctive geological and climatic conditions and history of Northeastern Brazil strongly constrained the formation of aquatic faunas in coastal basins of Maranhão State.

scholarly journals Composition, richness and nestedness of gallery forest bird assemblages in an Amazonian savanna landscape: lessons for conservation

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e12529
Author(s):  
Joandro Pandilha ◽  
José Júlio de Toledo ◽  
Luis Cláudio Fernandes Barbosa ◽  
William Douglas Carvalho ◽  
Jackson Cleiton de Sousa ◽  
...  
Keyword(s):  
Functional Diversity ◽  
Human Activities ◽  
Phylogenetic Diversity ◽  
Species Assemblages ◽  
Gallery Forest ◽  
Forest Species ◽  
Habitat Specificity ◽  
Bird Assemblages ◽  
Forest Bird ◽  
Gallery Forests

Gallery forests are important to the maintenance of a substantial portion of the biodiversity in neotropical savanna regions, but management guidelines specific to this forest type are limited. Here, we use birds as study group to assess if: (1) functional traits can predict the abundance and occupancy of forest species within a savanna landscape, (2) habitat structures influence the taxonomic, functional, and phylogenetic diversity of forest assemblages, and (3) less diverse gallery forest assemblages are a nested subset of more diverse assemblages living near continuous forests. Then, we propose strategies on how gallery forests can be managed to maintain their species assemblages amidst the fast expansion of human activities across tropical savanna landscapes. We studied 26 sites of gallery forests in an Amazonian savanna landscape and found that: (1) habitat specificity is the only functional trait that predicts species abundance and occupancy across a landscape; (2) phylogenetic diversity is negatively correlated with understory foliage density; (3) the percentage of forests and savannas around sites is positively correlated with both phylogenetic and functional diversity; (4) increasing human activities around gallery forest negatively influences taxonomic and functional diversity; and (5) forest bird assemblages are not distributed at random across the landscape but show a nested pattern caused by selective colonization mediated by habitat filtering. Our combined findings have three implications for the design of conservation strategies for gallery forest bird assemblages. First, maintaining the connectivity between gallery forests and adjacent continuous forests is essential because gallery forest bird assemblages are derived from continuous forest species assemblages. Second, because most species use the savanna matrix to move across the landscape, effectively managing the savanna matrices where gallery forests are embedded is as important to maintaining viable populations of forest bird species as managing the gallery forest themselves. Third, in savanna landscapes planned to be used for agriculture production, protecting gallery forests alone is not enough. Instead, gallery forests should be protected with surrounding savanna buffers to avoid the detrimental effects (edge effects and isolation) of human activities on their biodiversity.

scholarly journals Generating species assemblages for restoration and experimentation: A new method that can simultaneously converge on average trait values and maximize functional diversity

2018 ◽  
Vol 9 (7) ◽  
pp. 1764-1771 ◽  
Author(s):  
Daniel C. Laughlin ◽  
Loïc Chalmandrier ◽  
Chaitanya Joshi ◽  
Michael Renton ◽  
John M. Dwyer ◽  
...  
Keyword(s):  
Functional Diversity ◽  
New Method ◽  
Species Assemblages

Analyzing temporal trends in regional diversity: a biogeographic perspective

Paleobiology ◽  
2001 ◽  
Vol 27 (4) ◽  
pp. 631-645 ◽  
Author(s):  
Kaustuv Roy
Keyword(s):  
Climatic Change ◽  
Spatial Scales ◽  
Temporal Trends ◽  
Climatic Conditions ◽  
Species Range ◽  
Range Shifts ◽  
Species Assemblages ◽  
Regional Diversity ◽  
Biogeographic Provinces ◽  
Large Fluctuations

Evidence for species range shifts in response to climatic change is common in the Pleistocene and earlier fossil record. However, little work has been done to model how such shifts in species range limits would change compositions of species assemblages over different spatial scales. Here I present a simple model that explores the role of biogeography in constraining changes in the compositions of species assemblages under the null hypothesis of random range shifts. The model predicts that localities where most species are far away from the edges of their ranges (e.g., localities at the center of a biogeographic province) would show relatively stable diversity patterns even during episodes of climatic change. Only localities with many range endpoints (such as those near the edges of biogeographic provinces) would show large fluctuations in species composition (and richness) in response to changes in the ambient climatic conditions. I test the predictions of the model using (1) simulations and (2) the Pleistocene bivalve fauna of California. The simulations as well as the empirical data from the Pleistocene terraces are consistent with the model predictions. These results show that attempts to quantify temporal trends in local and regional diversity and assemblage compositions need to take biogeographic structure into account.

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

Density-based discrimination of protein and RNA in the ribosome

1992 ◽  
Vol 50 (1) ◽  
pp. 464-465
Author(s):  
Joachim Frank
Keyword(s):  
Transfer Function ◽  
Spatial Frequency ◽  
Three Dimensional ◽  
Wiener Filter ◽  
Dark Field Image ◽  
Dark Field ◽  
Frequency Range ◽  
Bright Field ◽  
Contrast Transfer Function ◽  
Pass Filter

Cryo-electron microscopy combined with single-particle reconstruction techniques has allowed us to form a three-dimensional image of the Escherichia coli ribosome.In the interior, we observe strong density variations which may be attributed to the difference in scattering density between ribosomal RNA (rRNA) and protein. This identification can only be tentative, and lacks quantitation at this stage, because of the nature of image formation by bright field phase contrast. Apart from limiting the resolution, the contrast transfer function acts as a high-pass filter which produces edge enhancement effects that can explain at least part of the observed variations. As a step toward a more quantitative analysis, it is necessary to correct the transfer function in the low-spatial-frequency range. Unfortunately, it is in that range where Fourier components unrelated to elastic bright-field imaging are found, and a Wiener-filter type restoration would lead to incorrect results. Depending upon the thickness of the ice layer, a varying contribution to the Fourier components in the low-spatial-frequency range originates from an “inelastic dark field” image. The only prospect to obtain quantitatively interpretable images (i.e., which would allow discrimination between rRNA and protein by application of a density threshold set to the average RNA scattering density may therefore lie in the use of energy-filtering microscopes.

Three-fold astigmatism: An important TEM aberration

1993 ◽  
Vol 51 ◽  
pp. 972-973 ◽  
Author(s):  
O.L. Krivanek ◽  
M.L. Leber
Keyword(s):  
High Resolution ◽  
Spatial Frequency ◽  
Field Emission ◽  
Azimuthal Angle ◽  
Hollow Cone ◽  
Small Probe ◽  
Wide Range ◽  
High Resolution Images ◽  
Image Position

Three-fold astigmatism resembles regular astigmatism, but it has 3-fold rather than 2-fold symmetry. Its contribution to the aberration function χ(q) can be written as:where A3 is the coefficient of 3-fold astigmatism, λ is the electron wavelength, q is the spatial frequency, ϕ the azimuthal angle (ϕ = tan-1 (qy/qx)), and ϕ3 the direction of the astigmatism.Three-fold astigmatism is responsible for the “star of Mercedes” aberration figure that one obtains from intermediate lenses once their two-fold astigmatism has been corrected. Its effects have been observed when the beam is tilted in a hollow cone over a wide range of angles, and there is evidence for it in high resolution images of a small probe obtained in a field emission gun TEM/STEM instrument. It was also expected to be a major aberration in sextupole-based Cs correctors, and ways were being developed for dealing with it on Cs-corrected STEMs.

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