Effects of nitrogen on properties of oxyfluoronitride bioglasses

Bioglasses are used as bone substitutes and prosthetic coatings. Following implantation, they are predisposed to generate a series of physicochemical reactions at the glass-bone interface. Bioglasses with molar composition: 55SiO₂–8.5CaO–31.5Na₂O–5CaF₂ have been synthesized and characterized. However, because of their poor strength, doping with nitrogen was performed on these glasses to increase their mechanical properties. These glasses were chemically analyzed to verify the amount of nitrogen introduced and structurally characterized by ²⁹Si and ¹⁹F MAS NMR. The fluorine complexes with calcium and sodium and is present as mixed calcium sodium fluoride and sodium fluoride species. The addition of fluorine to bioglasses reduces the melting temperature which helps to minimize nitrogen loss and bubble formation. So the fluorine facilitates the dissolution of nitrogen into the melt. Nitrogen substitutes for oxygen in the silicate network and is present as SiO₃N and SiO₂N₂ structural units. The density, glass transition temperature, Young's modulus, hardness and fracture toughness all increase with the content of nitrogen introduced into the glasses. These changes are a result of greater cross-linking of the silicate network due to the higher coordination of nitrogen compared to oxygen.     

Plant biodiversity patterns along a climatic gradient and across protected areas in West Africa

Knowledge of spatial patterns of biological diversity is fundamental for ecological and biogeographical analyses and for priority setting in nature conservation, particularly in West Africa where the existing high biodiversity is increasingly threatened by human activities. The maximum entropy approach was used to model the geographic distribution of 3,393 vascular plant species at a spatial resolution of 0.0833°. Species richness decreases along temperature and precipitation gradients with high species numbers in the south and lower numbers towards the north of the transect. All centres of plant species diversity are confined to humid areas in concordance with the high positive correlation between species richness and rainfall which appears to be the most important delimiter for the distribution ranges of many species in the area. The effectiveness of the existing protected areas at regional and national levels is investigated based on the proportion of species covered. Considering the whole study area, 95% of all species are covered by protected areas according to their distribution ranges. However, the proportion of species covered is considerably lower for some countries such as Benin and Togo. Our results could provide guidance for essential land use management interventions to decision‐makers and conservationists in the region.     

A Multidimensional Functional Trait Approach Reveals the Imprint of Environmental Stress in Mediterranean Woody Communities

Water availability is one of the most important factors determining species distribution, plant community structure and ecosystem functioning. We explore how the functional structure of Mediterranean woody plant communities varies along a regional gradient of aridity in the Andalusian region (south Spain). We question whether communities located in more arid sites show more similarity in their functional structure when compared with communities located in wetter sites or whether, instead, there is divergence in their functional spaces. We selected five aridity zones (three sampling sites per zone) and measured 13 traits of different functional dimensions (including leaf, stem and root traits) in 74 woody plant species. We quantified functional space differences using the n-dimensional niche space approach (hypervolume). We found a larger functional space for the wetter communities compared with the more arid communities, which showed greater overlap of the trait space occupation. Our results indicate that aridity acts as a key abiotic filter affecting various metrics of the community trait structure, in accordance with the plant economics spectrum. We have also documented consistent variation in the functional space, supporting lower functional diversity under more harsh climatic conditions. The trend of functional space variation along the aridity gradient was different when considering traits from only one plant organ. Thus, the filtering process driving the functional structure of the communities studied here largely depends on the trait axis considered; for example, the root dimension showed considerable variation in wet environments, whereas the leaf dimension exhibited a larger functional space in the drier habitats.     

A recent history of forest fragmentation in southwestern Ivory Coast

This study provides monitoring and spatial analysis of forest fragmentation based on high-resolution remote sensing, in order to give a framework for assessing residual biodiversity in the Guiglo-Taï region. Massive deforestation has taken place, mainly in the last 20 years, 79% of unprotected forests have been eliminated on the 100 × 100 km study area. Deforestation is also beginning to encroach on protected areas. Forest fragments are mainly found close to the deforestation front. In areas which were first deforested, forest fragments are very scarce and are restricted to less productive soils; they are often severely degraded. Young secondary forests develop on abandoned fields, but primary forest regeneration seems unlikely in light of the distance from seed sources and the increase in population pressure. Conservation initiatives in this zone of high biodiversity should focus on protected areas, taking into account short and long term benefits for the local population.     

Megafauna extinction,tree species range reduction,and carbon storage in Amazonian forests

During the Late Pleistocene and early Holocene 59 species of South American megafauna went extinct. Their extinction potentially triggered population declines of large‐seeded tree species dispersed by the large‐bodied frugivores with which they co‐evolved, a theory first proposed by Janzen and Martin (1982). We tested this hypothesis using species range maps for 257 South American tree species, comparing 63 species thought to be primarily distributed by megafauna with 194 distributed by other animals. We found a highly significant (p < 0.001) decreased mean range size of 26% for the megafauna dispersed fruit (n = 63 species) versus fruit dispersed by other animals (n = 194), results which support the hypothesis. We then developed a mathematical model of seed dispersal to estimate the theoretical impact of megafauna extinction on tree species range and found the estimated dispersal capacity (Φ_seed) of a 2 g seed decreases by > 95% following disperser extinction. A numerical gap dynamic simulations suggests that over a 10 000 yr period following the disperser extinctions, the average convex hull range size of large‐seeded tree species decreased by ～ 31%, while the estimated decrease in population size was ～ 54%, indicating a likely greater decrease in species population size than indicated by the empirical range patterns. Finally, we found a positive correlation between seed size and wood density of animal‐dispersed tree species implying that the Late Pleistocene and early Holocene megafaunal extinctions reduced carbon content in the Amazon by ～ 1.5 ± 0.7%. In conclusion, we 1) provide some empirical evidence that megafauna distributed fruit species have a smaller mean range size than wind, water or other animal‐dispersed species, 2) demonstrate mathematically that such range reductions are expected from megafauna extinctions ca 12 000 yr ago, and 3) illustrate that these extinctions may have reduced the Amazon's carbon storage capacity.     

A network approach for inferring species associations from co‐occurrence data

Positive and negative associations between species are a key outcome of community assembly from regional species pools. These associations are difficult to detect and can be caused by a range of processes such as species interactions, local environmental constraints and dispersal. We integrate new ideas around species distribution modeling, covariance matrix estimation, and network analysis to provide an approach to inferring non‐random species associations from local‐ and regional‐scale occurrence data. Specifically, we provide a novel framework for identifying species associations that overcomes three challenges: 1) correcting for indirect effects from other species, 2) avoiding spurious associations driven by regional‐scale distributions, and 3) describing these associations in a multi‐species context. We highlight a range of research questions and analyses that this framework is able to address. We show that the approach is statistically robust using simulated data. In addition, we present an empirical analysis of > 1000 North American tree communities that gives evidence for weak positive associations among small groups of species. Finally, we discuss several possible extensions for identifying drivers of associations, predicting community assembly, and better linking biogeography and community ecology.     

Antipeptide antibody against the human low-density-lipoprotein receptor. Characterization and cross-reactivity with bovine lymphocytes.

A dodecapeptide corresponding to the external N-terminal sequence of the human low-density-lipoprotein (LDL) receptor was synthesized. Antibodies raised in rabbits against the peptide were purified and were shown to react specifically with the peptide and with human LDL receptor of fibroblasts, HeLa cells and lymphocytes using binding studies and immunoblotting. By indirect immunogold analysis, antibodies bound to the LDL receptor of human lymphocytes could be revealed as clusters. Anti-receptor peptide immunoglobulins specifically bound to the human HeLa cell's LDL receptor with a lower affinity than LDL (Kd x 3). The anti-receptor peptide immunoglobulins and 125I-labelled-LDL competed with each other for the LDL-receptor sites. Antibodies failed to react with lymphocytes of subjects with the homozygous form of familial hypercholesterolaemia. Cross-reactivity with the dodecapeptide of the bovine LDL receptor was limited, but this cross-reactivity was confirmed by the binding of anti-receptor peptide immunoglobulins to the LDL receptor from bovine lymphocytes.