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Motivated by recent reports of a quantum-disordered ground state in the triangular lattice compound NaRuO2, we derive a jeff = 1/2 magnetic model for this system by means of first-principles calculations. The pseudospin Hamiltonian is dominated by bond-dependent off-diagonal Γ interactions, complemented by a ferromagnetic Heisenberg exchange and a notably antiferromagnetic Kitaev term. In addition to bilinear interactions, we find a sizable four-spin ring exchange contribution with a strongly anisotropic character, which has been so far overlooked when modeling Kitaev materials. The analysis of the magnetic model, based on the minimization of the classical energy and exact diagonalization of the quantum Hamiltonian, points toward the existence of a rather robust easy-plane ferromagnetic order, which cannot be easily destabilized by physically relevant perturbations.
Knowledge about the biogeographic affinities of the world’s tropical forests helps to better understand regional differences in forest structure, diversity, composition, and dynamics. Such understanding will enable anticipation of region-specific responses to global environmental change. Modern phylogenies, in combination with broad coverage of species inventory data, now allow for global biogeographic analyses that take species evolutionary distance into account. Here we present a classification of the world’s tropical forests based on their phylogenetic similarity. We identify five principal floristic regions and their floristic relationships: (i) Indo-Pacific, (ii) Subtropical, (iii) African, (iv) American, and (v) Dry forests. Our results do not support the traditional neo- versus paleotropical forest division but instead separate the combined American and African forests from their Indo-Pacific counterparts. We also find indications for the existence of a global dry forest region, with representatives in America, Africa, Madagascar, and India. Additionally, a northern-hemisphere Subtropical forest region was identified with representatives in Asia and America, providing support for a link between Asian and American northern-hemisphere forests.
Introduced species lists provide essential background information for biological invasions research and management. The compilation of these lists is, however, prone to a variety of errors. We highlight the frequency and consequences of such errors using introduced Melaleuca (sensu lato, including Callistemon) species in South Africa as a case study. We examined 111 herbarium specimens from South Africa and noted the categories and sub-categories of errors that occurred in identification. We also used information from herbarium specimens and distribution data collected in the field to determine whether a species was introduced, naturalized and invasive. We found that 72% of the specimens were not named correctly. These were due to human error (70%) (misidentification, and improved identifications) and species identification problems (30%) (synonyms arising from inclusion of Callistemon, and unresolved taxonomy). At least 36 Melaleuca species have been introduced to South Africa, and field observations indicate that ten of these have naturalized, including five that are invasive. While most of the errors likely have negligible impact on management, we highlight one case where incorrect identification lead to an inappropriate management approach and some instances of errors in published lists. Invasive species lists need to be carefully reviewed to minimise errors, and herbarium specimens supported by DNA identification are required where identification using morphological features is particularly challenging.
The Anthropocene Epoch is characterized by novel and increasingly complex dependencies between the environment and human civilization, with many challenges of biodiversity management emerging as wicked problems. Problems arising from the management of biological invasions can be either tame (with simple or obvious solutions) or wicked, where difficulty in appropriately defining the problem can make complete solutions impossible to find. We review four case studies that reflect the main goals in the management of biological invasions – prevention, eradication, and impact reduction – assessing the drivers and extent of wickedness in each. We find that a disconnect between the perception and reality of how wicked a problem is can profoundly influence the likelihood of successful management. For example, managing species introductions can be wicked, but shifting from species-focused to vector-focused risk management can greatly reduce the complexity, making it a tame problem. The scope and scale of the overall management goal will also dictate the wickedness of the problem and the achievability of management solutions (cf. eradication and ecosystem restoration). Finally, managing species that have both positive and negative impacts requires engagement with all stakeholders and scenario-based planning. Effective management of invasions requires either recognizing unavoidable wickedness, or circumventing it by seeking alternative management perspectives.
Many recent studies in invasion science have identified species traits that determine either invasiveness or impact. Such analyses underpin risk assessments and attempts to prioritise management actions. However, the factors that mediate the capacity of an introduced species to establish and spread (i.e. its invasiveness) can differ from those that affect the nature and severity of impacts. Here we compare those traits correlated with invasiveness with those correlated with impact for Cactaceae (“cacti”) in South Africa. To assess impact magnitude, we scored 70 cacti (35 invasive and 35 non-invasive species) using the Generic Impact Scoring System (GISS) and identified traits correlated with impact using a decision tree approach. We then compared the traits correlated with impact with those identified in a recent study as correlated with invasiveness (i.e. native range size and growth form). We found that there is a significant correlation between native range size and both invasiveness and impact. Cacti with larger native ranges were more likely to become invasive (p=0.001) and cause substantial impacts (p=0.01). These results are important for prioritising efforts on the management of cactus species. Understanding when and why impact and invasiveness are correlated (as they appear to be for Cactaceae) is likely to be an important area of future research in risk assessment.
In a recent Discussion Paper, Hoffmann and Courchamp (2016) posed the question: are biological invasions and natural colonisations that different? This apparently simple question resonates at the core of the biological study of human-induced global change, and we strongly believe that the answer is yes: biological invasions and natural colonisations differ in processes and mechanisms in ways that are crucial for science, management, and policy. Invasion biology has, over time, developed into the broader transdisciplinary field of invasion science. At the heart of invasion science is the realisation that biological invasions are not just a biological phenomenon: the human dimension of invasions is a fundamental component in the social-ecological systems in which invasions need to be understood and managed.
The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated (nine chemical transport models and two chemistry–climate models) by simulating the major natural bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2), over a 20-year period (1993–2012). Except for three model simulations, all others were driven offline by (or nudged to) reanalysed meteorology. The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences due to emissions and transport processes. Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA's long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements – including high-altitude observations from the NASA Global Hawk platform.
The models generally capture the observed seasonal cycle of surface CHBr3 and CH2Br2 well, with a strong model–measurement correlation (r ≥ 0.7) at most sites. In a given model, the absolute model–measurement agreement at the surface is highly sensitive to the choice of emissions. Large inter-model differences are apparent when using the same emission inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve best agreement to surface CHBr3 observations using the lowest of the three CHBr3 emission inventories tested (similarly, 8 out of 11 models for CH2Br2). In general, the models reproduce observations of CHBr3 and CH2Br2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific well. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr3 (and to a lesser extent CH2Br2) most elevated over the tropical western Pacific during boreal winter. The models also indicate the Asian monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models.
We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr3 and CH2Br2 of 2.0 (1.2–2.5) ppt, ∼ 57 % larger than the best estimate from the most recent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. The transport-driven interannual variability in the annual mean bromine SGI is of the order of ±5 %, with SGI exhibiting a strong positive correlation with the El Niño–Southern Oscillation (ENSO) in the eastern Pacific. Overall, our results do not show systematic differences between models specific to the choice of reanalysis meteorology, rather clear differences are seen related to differences in the implementation of transport processes in the models.
The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated, simulating the major natural bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2), over a 20-year period (1993-2012). The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences
due to emissions and transport processes. Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA’s long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements - including high altitude observations from the NASA Global Hawk platform.
The models generally capture the seasonal cycle of surface CHBr3 and CH2Br2 well, with a strong model measurement correlation (r ≥0.7) and a low sensitivity to the choice of emission inventory, at most sites. In a given model, the absolute model-measurement agreement is highly sensitive to the choice of emissions and inter-model differences are also apparent, even when using the same inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve optimal agreement to surface CHBr3 observations using the lowest of the three CHBr3 emission inventories tested (similarly, 8 out of 11 models for CH2Br2). In general, the models are able to reproduce well observations of CHBr3 and CH2Br2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr3 (and to a lesser extent CH2Br2) most elevated over the tropical West Pacific during boreal winter. The models also indicate the Asian Monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models.
We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr3 and CH2Br2 of 2.0 (1.2-2.5) ppt, ∼57% larger than the best estimate from the most re- cent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. However, transport-driven inter-annual variability in the annual mean bromine SGI is of the order of a ±5%, with SGI exhibiting a strong positive correlation with ENSO in the East Pacific
Men and women differ substantially regarding height, weight, and body fat. Interestingly, previous work detecting genetic effects for waist-to-hip ratio, to assess body fat distribution, has found that many of these showed sex-differences. However, systematic searches for sex-differences in genetic effects have not yet been conducted. Therefore, we undertook a genome-wide search for sexually dimorphic genetic effects for anthropometric traits including 133,723 individuals in a large meta-analysis and followed promising variants in further 137,052 individuals, including a total of 94 studies. We identified seven loci with significant sex-difference including four previously established (near GRB14/COBLL1, LYPLAL1/SLC30A10, VEGFA, ADAMTS9) and three novel anthropometric trait loci (near MAP3K1, HSD17B4, PPARG), all of which were significant in women, but not in men. Of interest is that sex-difference was only observed for waist phenotypes, but not for height or body-mass-index. We found no evidence for sex-differences with opposite effect direction for men and women. The PPARG locus is of specific interest due to its link to diabetes genetics and therapy. Our findings demonstrate the importance of investigating sex differences, which may lead to a better understanding of disease mechanisms with a potential relevance to treatment options.
Introduction: Researchers experience increasing pressures to connect with bodies that finance their projects. In this climate, critical scholars face many obstacles as they seek to navigate the treacherous waters of securing external funds. To debate these challenges, the ACME Editorial Collective organized a panel for the 2009 Annual Meeting of the Association of American Geographers in Las Vegas. This intervention represents a follow-up discussion and collective writing process among some of the panelists and members of the audience who attended the panel.
Below, we examine the neoliberalization of the current funding systems, discuss the implications for research practice, and make suggestions for critical engagement and transformation. Our suggestions, however, will not be easy to implement, as we can infer from the experience of the radical scholars of the post-1968 generation whose ascension into the upper echelons of North American and European university systems was also associated with the neoliberalization of the funding systems. This intervention represents a modest contribution in the tradition of critical research practice of creating the possibilities for progressive change.
The cloud forest amphibians and reptiles constitute the most important herpetofaunal segment in Honduras, due to the prevalence of endemic and Nuclear Middle American-restricted species. This segment, however, is subject to severe environmental threats due to the actions of humans. Of the 334 species of amphibians and reptiles currently known from Honduras, 122 are known to be distributed in cloud forest habitats. Cloud forest habitats are found throughout the mountainous interior of Honduras. They are subject to a Highland Wet climate, which features annual precipitation of >1500 mm and a mean annual temperature of <18°C. Cloud forest vegetation falls into two Holdridge formations, the Lower Montane Wet Forest and Lower Montane Moist Forest. The Lower Montane Wet Forest formation generally occurs at elevations in excess of 1500 m, although it may occur as low as 1300+ m at some localities. The Lower Montane Moist Forest formation generally occurs at 1700+ m elevation. Of the 122 cloud forest species, 18 are salamanders, 38 are anurans, 27 are lizards, and 39 are snakes. Ninety-eight of these 122 species are distributed in the Lower Montane Wet Forest formation and 45 in the Lower Montane Moist Forest formation. Twenty species are distributed in both formations. The cloud forest species are distributed among restricted, widespread, and peripheral distributional categories. The restricted species range as a group in elevation from 1340 to 2700 m, the species that are widespread in at least one of the two cloud forest formations range as a group from sea level to 2744 m, and the peripheral species range as a group from sea level to 1980 m. The 122 cloud forest species exemplify ten broad distributional patterns ranging from species whose northern and southern range termini are in the United States (or Canada) and South America, respectively, to those species that are endemic to Honduras. The largest segment of the herpetofauna falls into the endemic category, with the next largest segment being restricted in distribution to Nuclear Middle America, but not endemic to Honduras. Cloud forest species are distributed among eight ecophysiographic areas, with the largest number being found in the Northwestern Highlands, followed by the North-Central Highlands and the Southwestern Highlands. The greatest significance of the Honduran herpetofauna lies in its 125 species that are either Honduran endemics or otherwise Nuclear Middle American-restricted species, of which 83 are distributed in the country’s cloud forests. This segment of the herpetofauna is seriously endangered as a consequence of exponentially increasing habitat destruction resulting from deforestation, even given the existence of several biotic reserves established in cloud forest. Other, less clearly evident environmental factors also appear to be implicated. As a consequence, slightly over half of these 83 species (50.6%) have populations that are in decline or that have disappeared from Honduran cloud forests. These species possess biological, conservational, and economic significance, all of which appear in danger of being lost.
The conservation status of the members of the Honduran herpetofauna is discussed. Based on current and projected future human population growth, it is posited that the entire herpetofauna is endangered. The known herpetofauna of Honduras currently consists of 334 species, including 117 amphibians and 217 reptiles (including six marine reptiles, which are not discussed in this paper). The greatest number of species occur at low and moderate elevations in lowland and/or mesic forest formations, in the Northern and Southern Cordilleras of the Serranía, and the ecophysiographic areas of the Caribbean coastal plain and foothills. Slightly more than one-third of the herpetofauna consists of endemic species or those otherwise restricted to Nuclear Middle America. Honduras is an area severely affected by amphibian population decline, with close to one-half of the amphibian fauna threatened, endangered, or extinct. The principal threats to the survival of members of the herpetofauna are uncontrolled human population growth and its corollaries, habitat alteration and destruction, pollution, pest and predator control, overhunting, and overexploitation. No Honduran amphibians or reptiles are entirely free of human impact. A gauge is used to estimate environmental vulnerability of amphibian species, using measures of extent of geographic range, extent of ecological distribution, and degree of specialization of reproductive mode. A similar gauge is developed for reptiles, using the first two measures for amphibian vulnerability, and a third scale for the degree of human persecution. Based on these gauges, amphibians and reptiles show an actual range of Environmental Vulnerability Scores (EVS) almost as broad as the theoretical range. Based on the actual EVS, both amphibian and reptilian species are divided into three categories of low, medium, and high vulnerability. There are 24 low vulnerability amphibians and 47 reptiles, 43 medium vulnerability amphibians and 111 reptiles, and 50 high vulnerability amphibians and 53 reptiles. Theoretical EVS values are assessed against available information on current population status of endemic and Nuclear Middle American taxa. Almost half (48.8%) of the endemic species of Honduran amphibians are already extinct or have populations that are in decline. Populations of 40.0% of the Nuclear Middle American amphibian species are extirpated or in decline. A little less than a third (27.0%) of the endemic reptiles are thought to have declining populations. Almost six of every ten (54.5%) of the Nuclear Middle American reptilian species are thought to have declining populations. EVS values provide a useful indicator of potential for endangerment, illustrating that the species whose populations are currently in decline or are extinct or extirpated have relatively high EVS. All high EVS species need to be monitored closely for changes in population status. A set of recommendations are offered, assuming that biotic reserves in Honduras can be safeguarded, that it is hoped will lead to a system of robust, healthy, and economically self-sustaining protected areas for the country’s herpetofauna. These recommendations will have to be enacted swiftly, however, due to unremitting pressure from human population growth and the resulting deforestation.
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt[sNN] = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.
Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.