Aim The aim was to examine the links between past biome stability, vegetation dynamics and biodiversity patterns. Location South America. Time period Last 30,000 years. Major taxa studied Plants. Methods We classified South America into major biomes according to their dominant plant functional groups (grasses, trees and shrubs) and ran a random forest (RF) classification with data on current climate. We then fitted the algorithm to predict biome distributions for every 1,000 years back to 21,000 yr BP and estimated biome stability by counting how many times a change in climate was predicted to shift a grid cell from one biome to another. We compared our model‐based stability map with empirical estimates from selected pollen records covering the past 30 kyr in terms of vegetation shifts, changes in species composition and time‐lag of vegetation responses. Results We found a strong correlation between our habitat stability map and regional vegetation dynamics. Four scenarios emerged according to the way forest distribution shifted during a climate change. Each scenario related to specific regional features of biome stability and diversity, allowing us to formulate specific predictions on how taxonomic, genetic and functional components of biodiversity might be impacted by modern climate change. Main conclusions Our validated map of biome stability provides important baseline information for studying the impacts of past climate on biodiversity in South America. By focusing exclusively on climatic changes of manifested relevance (i.e., those resulting in significant habitat changes), it provides a novel perspective that complements previous datasets and allows scientists to explore new questions and hypotheses at the local, regional and continental scales.

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The oxidation of L-ascorbic acid by aquated Fe(III) ions was studied as a function of [Cl"], [H+], temperature, and pressure. The reaction is significantly accelerated by the presence of chloride ions, which is ascribed to the higher redox reactivity of Fe(H20)5Cl2+ and Fe(H20)4(0H)Cl+ as compared to the corresponding aqua complexes. The inverse [H+] dependence of the redox reaction is ascribed to the deprotonation of Fe(H20)63+ to produce the more labile Fe(H20)50H2+ species. From a comparison of the measured activation parameters for the redox reaction (AH*, 51*, and *) with those for solvent exchange on Fe(H20)63+ and Fe(H20)50H2+, it is concluded that the oxidation of L-ascorbic acid by these two Fe(III) species occurs according to different mechanisms. The reaction follows an outer-sphere mechanism for the oxidation by the more inert Fe(H20)63+ species but an inner-sphere mechanism for the more labile Fe(H20)50H2+ species. A comparison of the experimental rate constants with those calculated from the Marcus cross relationship confirms the interpretation.

Aim Closely related species are expected to be similar in their ecological attributes. However, clades colonizing new environments and diversifying due to ecological processes often show morphological and ecological divergence. Canids arrived in South America after the formation of the Isthmus of Panama and diversified to occupy a variety of habitats. We test whether the diversification of this group was followed by divergence in species niches. If ecological processes are associated with species divergences, we expect to see species occupying distinct climatic niches, showing divergent phenotypes, and showing a close association between their phenotypes and ecological attributes. Location South AmericaMethods We use comparative and multivariate climatic niche analysis, geometric morphometric (skull and jaw), and distance-based phylogenetic regressions to test whether the diversification of South American canids was followed by divergence in their climatic niches and phenotypic traits. ResultsWe found a pattern of continental niche occupancy (north to south) along a complex climatic gradient. As species diverged, they evolved distinct climatic tolerances. Climatic niche similarities are not related to species phylogenetic relationships, indicating that closely related species may have distinct climatic tolerances. Our morphological analysis also showed strong phenotypic divergence between species. Our results suggest that these differences were related to climatic and trophic niches. Results show divergent phenotypes in both the skull and jaw, and that there is a close association between phenotype and ecological strategies.Main conclusions Our study integrates phylogenetic history, ecological and morphological data to study the evolution of South American canids. Canid colonization of South America was followed by species ecological divergences. Our results support the hypothesis that ecological processes are the main drivers of diversification of this clade and illustrate a complex biogeographical history of ecological diversification of canids at continental scale.

Summary1. The variation in cranial size of the crab-eating fox Cerdocyon thous was analysed in relation to latitude and several environmental variables throughout its distribution in South America. 2. We tested the existence of clines to determine whether this canid follows Bergmann's rule to the north and south of the Equator. Also, using niche modelling, we analysed whether the climatic changes during the last glaciation could have influenced Bergmann's rule in this species. We quantified the size of the cranium of C. thous (n = 300). The data were divided into two groups: (i) south of the Equator (n = 163) and (ii) north of the Equator (n = 137). We performed correlations, OLS regressions and simultaneous autoregressions to analyse the relationship between the variation in size and different geographic and environmental variables. Data of occurrence (n = 594) together with ambient variables from the present and the last glacial maximum (LGM) were used to predict the occurrence of C. thous with the implementation of the maximum entropy method. Present-day and historical distribution maps were obtained. 3. The variation in the size of the cranium of C. thous showed two trends. In the south of Equator, we observed that the size of the skull shows an inverse relationship with temperature-related variables and a positive one with precipitation, while in north of the Equator, we observed the opposite relationship. Populations south of the Equator follow Bergmann's rule showing increasing size with increasing latitude. To the north of the Equator, a non-Bergmannian pattern occurs because size decreases with increasing latitude. 4. Niche modelling showed two present-day groupings in South America, one north of Amazonia and the other south. However, for the period of the LGM, four groups emerged, possibly related to the four subspecies presently described for C. thous. Therefore, it is possible that the observed pattern -southern populations following Bergmann's rule while northern populations reflecting the opposite -has been influenced by the events that occurred during the LGM that could have led to the differentiation of populations.

Pure and single phase thorium−uranium(IV) phosphate-diphosphate β-TUPD (orthorhombic form) dense pellets were prepared by two wet chemical routes from low-temperature precursors. The first method was based on the “direct evaporation” of a mixture containing tetravalent actinides and phosphoric acid while the second one involved the initial precipitation of the thorium−uranium(IV) phosphate−hydrogenphosphate hydrate (TUPHPH). Both methods led to single phase sintered samples following a two-step procedure using a uniaxial pressing at room temperature and then a heat treatment at high temperature. The dilatometric study and the determination of the linear shrinkage of the pellets showed that the best densification of the samples prepared via the “precipitation” method was obtained after heating the raw pellet at 1250 °C for 5 h, for initial uranium amount lower than 44.5 wt %(U). For samples prepared via “direct evaporation”, the heat treatment must be prolonged for at least 15 h at this temperature. Moreover, the complete characterization of the samples (EPMA, and so forth) confirmed that the homogeneity of the samples was significantly improved when using TUPHPH as a precursor, probably due to the better reactivity of the initial powder (higher specific surface area, smaller grain size, and so forth). Several leaching tests were performed in various acidic media and in natural waters on β-TUPD sintered samples. All the corresponding normalized dissolution rates remained low (10-6 to 10-5 g/(m2 day)) even in aggressive media which confirms the high chemical durability of β-TUPD, thus enhancing the potential use of this ceramic in the field of the efficient immobilization of tetravalent actinides.