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.     

Membrane thickness changes ion-selectivity of channel-proteins.

The plasma membrane is a highly dynamic cell-barrier if the nature and distribution of its constituents are considered. Ion channels are embedded in these double lipid bilayers, which modulate their 3D-structures. The structure modulations by the lipid bilayer can assume such a degree that channel activation depends on them, as was shown for the KcsA potassium channel. Here we show that the cation-over-anion selectivity of reconstituted ICln channels can be varied by the thickness of a bilayer build of phosphatidylcholines. The shorter the acyl-chains and therefore the thinner the bilayers of the membrane are, the more potassium selective the channels are. In contrast, the longer the acyl-chains and therefore the thicker the membranes are, the more chloride selective the channels become.     

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.     

Analysis of the tet gene of plasmid pCIS7 isolated from Bacillus subtilis

We have previously shown that plasmid pCIS7, which contains 11.5 kb of Bacillus subtilis DNA isolated from a tetracycline-sensitive (TcS) strain, confers Tc resistance when integrated and amplified in the chromosome of TcS B. subtilis 168trpC2 [Ives and Bott, J. Bacteriol. 171 (1989) 1801-1810]. Here, we report that the number of integrated plasmid sequences required to confer Tc resistance is greater than the 20 copies seen with increasing chloramphenicol selection and, by dot-blot analysis, exceeds 100 copies per cell. The amplification is accompanied by a corresponding increase in mRNA encoding the tet gene. The tet gene sequence of pCIS7 has been compared to B. subtilis tetGSY908 [Sakaguchi et al., Biochim. Biophys. Acta. 94 (1988) 49-57] and other Gram-positive tet genes. The tet gene of pCIS7 is a member of the class L TcR determinants, and probably confers Tc resistance by increasing the efflux of Tc from the bacterial cell.     

Acrylamide Gel Electrophoresis of Intracellular Proteins During Early Stages of Sporulation in Bacillus subtilis

Acrylamide gel electrophoresis of unfractionated cellular extracts of Bacillus subtilis is shown to be an effective method for characterizing many of the changes in protein composition, when coupled with specific histological-type staining reactions. The results obtained here by using extracts from cells at different stages of growth and sporulation are consistent with observations from other laboratories where extensively purified and highly characterized enzymes have been studied. In several instances, the histochemical reactions can be associated with a specific enzymatic function and appear to indicate the presence of multiple molecular forms. In other instances, the data cannot be evaluated in terms of known enzyme function because the specificity of the histochemical analysis is not certain. However, the assays described permit monitoring of electrophoretic changes at the level of individual proteins within sporulating cultures. The results suggest that B. subtilis may contain two "hexokinase-like" enzymes which cease to function before sporulation is initiated. Aldolase and alanine dehydrogenase are detectable as single bands of enzyme activity during vegetative growth but as multiple molecular forms once sporulation has been initiated. Reduced nicotinamide adenine dinucleotide dehydrogenase activity is represented by an entire family of reactive species in these crude extracts, which undergo multiple changes during the early stages of sporulation. Tricarboxylic acid cycle dehydrogenase enzymes and those bands having esterase activity on alpha-naphthyl acetate show detectable changes in specific activity after cessation of exponential growth. Glucose dehydrogenase is not detectable until the sequence of changes leading to spore formation has progressed for 4 or 5 hr.