bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular characterization of the β‐lactamases in Escherichia coli and Klebsiella pneumoniae from a tertiary care hospital in Riyadh, Saudi Arabia
Authors: Marie Mohammed Ali , John James , Krishnappa Lakshmana Gowda , Gopalkrishnan Sangeetha 
Published: October 2013

ABSTRACTThe widespread use of antimicrobials has increased the occurrence of multidrug resistant microbes. The commonest mechanism of antimicrobial resistance in Enterobacteriaceae is production of β‐lactamases such as metallo‐β‐lactamases (MBL) and extended spectrum β‐lactamases (ESBL). Few studies have used a molecular approach to characterize the prevalence of β‐lactamases. Here, the prevalence of different β‐lactamases was characterized by performing three multiplex PCRs targeting genes similar to those described in earlier publications. Antimicrobial susceptibility tests for all isolates were performed using the agar dilution method. β‐lactamase was detected in 72% of the isolates, the detection rate being 64% in 2011 and 75% in 2012. The isolates were highly resistant to carbapenems such as meropenem and imipenem and susceptible to colistin and tigecycline. In this study, 22% of isolates contained both MBL and ESBL. ESBL was detected more frequently in Escherichia coli isolates, whereas carbapenemase was detected more frequently in Klebsiella pneumoniae isolates. These findings suggest the spread of multi‐resistant ESBL and MBL producers in the community. Our results have implications for patient treatment and also indicate the need for increased surveillance and molecular characterization of isolates.
Different antigenicities of the N‐terminal region of cellular and scrapie prion proteins
Authors: Ushiki‐Kaku Yuko , Iwamaru Yoshifumi , Masujin Kentaro , Imamura Morikazu , Itohara Shigeyoshi , Ogawa‐Goto Kiyoko , Hattori Shunji , Yokoyama Takashi 
Published: October 2013

ABSTRACTLimited information is available about conformational differences between the abnormal isoform of prion protein (PrPSc) and cellular prion protein (PrPC) under native conditions. To clarify conformational differences between these two isoforms, PrP‐deficient mice were immunized with brain homogenates of normal and scrapie‐infected animals. All mice generated anti‐PrP antibodies. Peptide array analysis of these serum samples revealed a distinctive epitope of PrPSc consisting of QGSPGGN (PrP41–47) at the N‐terminus. This study demonstrated a conformational dissimilarity at the N‐terminus between PrPSc and PrPC, a finding that may provide novel information about conformational features of PrPSc.
A decade of free‐air CO2 enrichment increased the carbon throughput in a grass‐clover ecosystem but did not drastically change carbon allocation patterns
Authors: Staddon Philip L. , Reinsch Sabine , Olsson Pål A. , Ambus Per , Lüscher Andreas , Jakobsen Iver 
Published: October 2013

Summary

The response of the soil carbon cycle to increasing atmospheric CO2 concentration has far reaching consequences for the ecosystem carbon balance under future climatic conditions. We report on work carried out in the Swiss free‐air CO2 enrichment (FACE) experiment, where we used in situ 13CO2 labelling to determine whether elevated CO2 (+230 μL L−1) concentration changes the fate of recently assimilated carbon in the soil microbial community.

Elevated CO2 (eCO2) concentration had an overall positive effect on microbial abundance (P < 0·001) with the gram‐negative bacteria showing significantly increased quantities.

Gram‐negative bacteria and saprotrophic fungi tended to utilize a higher amount of recently assimilated carbon under eCO2. Arbuscular mycorrhizal fungi (AMF) utilized plant‐assimilated carbon within 1 day after the 13CO2 pulse and 13C uptake patterns in AMF suggest that carbon transfer is faster under eCO2 concentration than under ambient CO2 (aCO2). Additionally, the respiration of recently assimilated carbon was significantly higher under eCO2 than aCO2 concentration.

Our data suggest that elevated atmospheric CO2 concentration accelerated and increased the utilization of recently assimilated carbon by the microbial community without changing the microbial community composition drastically.

We conclude that a higher standing soil microbial biomass under eCO2 concentration was the key cause for the higher carbon flow through the plant–soil system. Carbon utilization by microbial functional groups was only little affected by a decade of CO2 enrichment.
Heterogeneity of reproductive age increases the viability of semelparous populations
Authors: Acker Paul , Robert Alexandre , Bourget Romain , Colas Bruno 
Published: October 2013

Summary

One important feature of natural populations is that individuals of the same age or functional class at a given time may vary in their demographic rates, such as their survival probabilities or fecundities. This demographic heterogeneity is due to the plastic response of individuals to spatially variable environmental conditions, to genetic variation or to maternal or cohort effects. Although demographic heterogeneity may have serious consequences, it is generally not included in models of population dynamics. The interactions of demographic heterogeneity with environmental stochasticity and density dependence are poorly understood, as are its consequences for population viability.

We explored the effect of heterogeneity in age at reproduction on the dynamics and viability of semelparous populations. We developed individual‐based models according to which individuals had to follow a particular life path in a multifurcated life cycle. We used data from a well‐studied monocarpic plant, Centaurea corymbosa, to calibrate the models with realistic distributions of demographic parameters.

Disregarding the trivial effect of changing generation time, we found that heterogeneous populations had higher viability than homogeneous populations due to the desynchronization of demographic processes among individuals.

Heterogeneity buffers the negative impact of environmental stochasticity by reducing the covariation of life histories among individuals (i.e. the bet‐hedging effect). In addition, when negative density dependence is implemented, desynchronization in heterogeneous populations reduces intraspecific competition. Indeed, crowded cohorts, occurring randomly due to demographic or environmental stochasticity, can spread their offspring over several years, which limits negative interactions among individuals due to resource limitations (in this study, a fixed number of microsites for seedlings). These effects are likely to occur in every semelparous population.

Our results allow us to better understand the functional links between the heterogeneity, desynchronization, dynamics and viability of populations facing spatial and temporal variations in their environments. These links suggest that demographic heterogeneity, regardless of its causes (genetic variation or plasticity), is an important component of population dynamics. Neglecting demographic heterogeneity leads to overestimating the level of synchronization among individuals, which may in turn strongly bias viability assessments in realistic environments.
Extended structure tensors for multiple directionality estimation
Authors: Andersson Fredrik , Duchkov Anton A. 
Published: October 2013

ABSTRACTStandard structure tensors provide a robust way of directionality estimation of waves (or edges) but only for the case when they do not intersect. In this work, a structure tensor extension using a one‐way wave equation is proposed as a tool for estimating directionality in seismic data and images in the presence of conflicting dips. Detection of two intersecting waves is possible in a two‐dimensional case. In three dimensions both two and three intersecting waves can be detected. Moreover, a method for directionality filtering using the estimated directions is proposed. This method makes use of the ideas of a one‐way wave equation but can be applied to generic images not related to wave propagation.
Trophic niche width increases with bill‐size variation in a generalist passerine: a test of niche variation hypothesis
Authors: Hsu Yu‐Cheng , Shaner Pei‐Jen , Chang Chun‐I , Ke Linhua , Kao Shuh‐Ji 
Published: October 2013

Summary

The niche variation hypothesis (NVH) predicts that populations with wider niches are phenotypically more variable than populations with narrower niches, which is frequently used to explain diversifying processes such as ecological release. However, not all empirical evidence supports the NVH. Furthermore, a relationship between population phenotypic variation and niche width can be caused by sexual selection or environmental gradients, which should be carefully considered along with competition in explaining niche variation.

In this study, we used eight populations of a generalist passerine species, Paradoxornis webbianus (vinous‐throated parrotbill), to test the NVH. We assessed evidence of ecological sexual dimorphism and environmental gradients in bill morphology of P. webbianus. A total of 170 P. webbianus from eight sites ranging 24–2668 m in altitude were included in this study. We used two principal components to quantify bill morphology: one describes bill size and the other describes bill slenderness. We used stable carbon and nitrogen isotope values of bird feathers to quantify trophic positions, and we estimated population trophic niche width using Bayesian standardized ellipse area.

Paradoxornis webbianus with larger and more slender bills fed at higher trophic levels and population trophic niche width tended to increase with bill‐size variation, supporting the NVH. The males had larger bills and marginally higher nitrogen isotope values than the females, suggesting ecological sexual dimorphism. Despite a positive correlation between bill size and wing length indicating sexual selection for larger male size, only three of the eight populations showed both male‐biased bill size and male‐biased wing length. Sexual dimorphism explained 13%–64% of bill‐size variation across sites, suggesting its role in niche variation could vary greatly among populations. The variation in bill slenderness in P. webbianus increased with elevation. However, neither bill‐size variation nor trophic niche width changed with elevation. Therefore, environmental gradients that could be reflected in the elevation are not likely to drive the observed morphological and niche variation.

This study provides an empirical case for the NVH and highlights the importance of investigating sexual dimorphism and environmental gradients in studies of niche dynamics.
Dispersal in a patchy landscape reveals contrasting determinants of infection in a wild avian malaria system
Authors: Knowles Sarah C. L. , Wood Matthew J. , Alves Ricardo , Sheldon Ben C. 
Published: October 2013

SummaryUnderstanding exactly when, where and how hosts become infected with parasites is critical to understanding host–parasite co‐evolution in natural populations. However, for host–parasite systems in which hosts or parasites are mobile, for example in vector‐borne diseases, the spatial location of infection and the relative importance of parasite exposure at successive host life‐history stages are often uncertain.Here, using a 6‐year longitudinal data set from a spatially referenced population of blue tits, we test the extent to which infection by avian malaria parasites is determined by conditions experienced at natal or breeding sites, as well as by postnatal dispersal between the two.We show that the location and timing of infection differs markedly between two sympatric malaria parasite species. For one species (Plasmodium circumflexum), our analyses indicate that infection occurs after birds have settled on breeding territories, and because the distribution of this parasite is temporally stable across years, hosts born in malarious areas could in principle alter their exposure and potentially avoid infection through postnatal dispersal. Conversely, the spatial distribution of another parasite species (Plasmodium relictum) is unpredictable and infection probability is positively associated with postnatal dispersal distance, potentially indicating that infection occurs during this major dispersal event.These findings suggest that hosts in this population may be subject to divergent selection pressures from these two parasites, potentially acting at different life‐history stages. Because this implies parasite species‐specific predictions for many coevolutionary processes, they also illustrate the complexity of predicting such processes in multi‐parasite systems.
Effects of plant phylogenetic diversity on herbivory depend on herbivore specialization
Authors: Castagneyrol Bastien , Jactel Hervé , Vacher Corinne , Brockerhoff Eckehard G. , Koricheva Julia 
Published: October 2013

Summary

Pest regulation is an important ecosystem service provided by biodiversity, as plants growing in species‐rich communities often experience associational resistance to herbivores. However, little is known about the respective influence of the quantity and identity of associated species on herbivory in focal plants.

Using a meta‐analysis to compare insect herbivory in pure and mixed forests, we specifically tested the effects of the relative abundance of focal tree species and of phylogenetic distance between focal and associated tree species on the magnitude of associational resistance.

Overall, insect herbivory was significantly lower in mixed forests, but the outcome varied greatly depending on the phylogenetic relatedness among tree species and the degree of herbivore feeding specialization.

Specialist herbivore damage or abundance was positively related to relative abundance of their host trees, regardless of the phylogenetic distance between host and associated tree species.

By contrast, tree diversity triggered associational resistance to generalist herbivores only when tree mixtures included tree species phylogenetically distant to the focal species.

Synthesis and applications. Our study demonstrates that the establishment of mixed forests per se is not sufficient to convey associational resistance to herbivores if the identity of tree species associated in mixtures is not taken into account. As a general rule, mixing phylogenetically more distinct tree species, such as mixtures of conifers and broadleaved trees, results in more effective reduction in herbivore damage.
Facilitative or competitive effects of woody plants on understorey vegetation depend on N‐fixation, canopy shape and rainfall
Authors: Blaser Wilma J. , Sitters Judith , Hart Simon P. , Edwards Peter J. , Olde Venterink Harry 
Published: October 2013

Summary

A recent meta‐analysis suggested that differences in rainfall are a cause of variation in tree–grass interactions in savannas, with trees facilitating growth of understorey grasses in low‐rainfall areas, but competing with them under higher rainfall. We hypothesized that this effect of rainfall upon understorey productivity is modified by differences in the growth form of the woody plants (i.e. the height of the lower canopy) or by their capacity to fix nitrogen.

We performed a meta‐analysis of the effects of woody plants on understorey productivity, incorporating canopy height and N‐fixation, and their interaction with rainfall.

N‐fixing woody plants enhanced understorey productivity, whereas non‐fixers had a neutral or negative effect, depending on high or low canopy, respectively. We found a strong negative correlation between rainfall and the degree to which trees enhanced understorey productivity, but only for trees with a high canopy.

Synthesis. The effect of woody plants on understorey productivity depends not only on rainfall, but also on their growth form and their capacity to fix N. Facilitation occurs mostly when woody plants ameliorate both water and nitrogen conditions. However, a low canopy suppresses understorey vegetation by competing for light, regardless of water and nutrient relations.
Decomposing recruitment limitation for an avian‐dispersed rain forest tree in an anciently fragmented landscape
Authors: Núñez‐Ávila Mariela C. , Uriarte María , Marquet Pablo A. , Armesto Juan J. 
Published: October 2013

SummaryForest fragmentation may intensify recruitment limitation through impacts on seed production, dissemination and seedling establishment processes. In an ancient mosaic of fog‐dependent rain forest patches on coastal hilltops of semi‐aridChile (30 °S), we investigated how aridity‐driven habitat fragmentation affected the recruitment of the fleshy‐fruited, dioecious treeAextoxicon punctatum(Aextoxicaceae) and the role of birds in seed dispersal across patches.We hypothesized that reduced fragment size enhanced recruitment limitation due to constraints on tree fecundity, avian disperser activity and seedling recruitment, caused primarily by strong edge effects in small fragments.We mapped adultAextoxicontrees and placed 686 seed traps distributed in 3 small (<0.3 ha) and 3 large patches ( > 0.9 ha) in the forest patch mosaic. To identify seed sources, endocarps of 282 dispersed seeds from seed traps were genotyped and compared with 155 genotyped females using nine microsatellite markers. Seed dispersal curves for different forest patches were constructed using maximum likelihood methods. Further, seed addition experiments were conducted in the six fragments to assess recruitment probabilities.Lower density and basal areas of reproductive female trees, in addition to shorter fruiting periods and lower seed yields, led to strong source limitation in small patches. Three bird species accounted for the bulk of visits to fruiting trees, but were less active in smaller patches. Dispersal curves were strongly leptokurtic with maximum dispersal distances related to the shape of patches. Important proportions (5–40%) of genotyped seeds in all patches were immigrants. However, seeds arrived mainly at patch edges or below reproductive trees where germination and survival are reduced. Fewer seedlings originated from experimentally added seeds in small patches subjected to greater edge effects.Synthesis. In summary, we provide evidence for source, dispersal and establishment limitation of this dioecious tree in an aridity‐driven fragmented landscape. Small fragment size and edge effects had negative impacts on fecundity and seedling establishment. Although bird‐mediated seed dispersal favoured immigration between patches, recruitment from such seeds will be unlikely because of low quality of deposition sites.
Waiting for Gajah: an elephant mutualist's contingency plan for an endangered megafaunal disperser
Authors: Sekar Nitin , Sukumar Raman 
Published: October 2013

Summary

Large animals are disproportionately likely to go extinct, and the effects of this on ecosystem processes are unclear. Megaherbivores (weighing over 1000 kg) are thought to be particularly effective seed dispersers, yet only a few plant species solely or predominantly adapted for dispersal by megaherbivores have been identified.

The reasons for this paradox may be elucidated by examining the ecology of so‐called megafaunal fruiting species in Asia, where large‐fruited species have been only sparsely researched. We conducted focal tree watches, camera trapping, fruit ageing trials, dung seed counts and germination trials to understand the ecology of Dillenia indica, a large‐fruited species thought to be elephant‐dispersed, in a tropical moist forest (Buxa Tiger Reserve, India).

We find that the initial hardness of the fruit of D. indica ensures that its small (˜6 mm) seeds will primarily be consumed and dispersed by elephants and perhaps other megaherbivores. Elephants removed 63.3% of camera trap‐monitored fruits taken by frugivores.

If the fruit of D. indica is not removed by a large animal, the seeds of D. indica become available to successively smaller frugivores as its fruits soften.

Seeds from both hard and soft fruits are able to germinate, meaning these smaller frugivores may provide a mechanism for dispersal without megaherbivores.

Synthesis. Dillenia indica's strategy for dispersal allows it to realize the benefits of dispersal by megaherbivores without becoming fully reliant on these less abundant species. This risk‐spreading dispersal behaviour suggests D. indica will be able to persist even if its megafaunal disperser becomes extinct.
Biological Flora of the British Isles: Robinia pseudoacacia
Authors: Cierjacks Arne , Kowarik Ingo , Joshi Jasmin , Hempel Stefan , Ristow Michael , von der Lippe Moritz , Weber Ewald 
Published: October 2013

Summary

This account presents information on all aspects of the biology of Robinia pseudoacacia L. that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history and conservation.

Robinia pseudoacacia, false acacia or black locust, is a deciduous, broad‐leaved tree native to North America. The medium‐sized, fast‐growing tree is armed with spines, and extensively suckering. It has become naturalized in grassland, semi‐natural woodlands and urban habitats. The tree is common in the south of the British Isles and in many other regions of Europe.

Robinia pseudoacacia is a light‐demanding pioneer species, which occurs primarily in disturbed sites on fertile to poor soils. The tree does not tolerate wet or compacted soils. In contrast to its native range, where it rapidly colonizes forest gaps and is replaced after 15–30 years by more competitive tree species, populations in the secondary range can persist for a longer time, probably due to release from natural enemies.

Robinia pseudoacacia reproduces sexually, and asexually by underground runners. Disturbance favours clonal growth and leads to an increase in the number of ramets. Mechanical stem damage and fires also lead to increased clonal recruitment.

The tree benefits from di‐nitrogen fixation associated with symbiotic rhizobia in root nodules. Estimated symbiotic nitrogen fixation rates range widely from 23 to 300 kg ha−1 year−1. The nitrogen becomes available to other plants mainly by the rapid decay of nitrogen‐rich leaves.

Robinia pseudoacacia is host to a wide range of fungi both in the native and introduced ranges. Megaherbivores are of minor significance in Europe but browsing by ungulates occurs in the native range. Among insects, the North American black locust gall midge (Obolodiplosis robiniae) is specific to Robinia and is spreading rapidly throughout Europe.

In parts of Europe, Robinia pseudoacacia is considered an invasive non‐indigenous plant and the tree is controlled. Negative impacts include shading and changes of soil conditions as a result of nitrogen fixation.