Dominant Gradient Research Articles

Deepcoral habitats of Glacier Bay National Park and Preserve, Alaska.

Glacier Bay National Park and Preserve (GBNPP) in Southeast Alaska is a system of glaciated fjords with a unique and recent history of deglaciation. As such, it can serve as a natural laboratory for studying patterns of distribution in marine communities with proximity to glacial influence. In order to examine the changes in fjord-based coral communities, underwater photo-quadrats were collected during multipurpose dives with a remotely operated vehicle (ROV) in March of 2016. Ten sites were chosen to represent the geochronological and oceanographic gradients present in GBNPP. Each site was surveyed vertically between 100 and 420 meters depth and photo-quadrats were extracted from the video strip transects for analysis. The ROV was equipped with onboard CTD which recorded environmental data (temperature and salinity), in order to confirm the uniformity of these characteristics at depth across the fjords. The percent cover and diversity of species were lowest near the glaciated heads of the fjords and highest in the Central Channel and at the mouths of the fjords. Diversity is highest where characteristics such as low sedimentation and increased tidal currents are predominant. The diverse communities at the mouths of the fjords and in the Central Channel were dominated by large colonies of the Red Tree Coral, Primnoa pacifica, as well as sponges, brachiopods, multiple species of cnidarians, echinoderms, molluscs and arthropods. The communities at the heads of the fjords were heavily dominated by pioneering species such as brachiopoda, hydrozoan turf, the encrusting stoloniferan coral Sarcodyction incrustans, and smaller colonies of P. pacifica. This research documents a gradient of species dominance from the Central Channel to the heads of the glaciated fjords, which is hypothesized to be driven by a combination of physical and biological factors such as glacial sedimentation, nutrient availability, larval dispersal, and competition.

Plant Functional Niches in Forests Across Four Climatic Zones: Exploring the Periodic Table of Niches Based on Plant Functional Traits.

Previous studies have indicated that a niche variation scheme, similar to the periodic table of elements, can be constructed based on functional traits. The periodic table of niches for species is defined as a multidimensional ordination scheme of niche relationships and their orders in a specific biotic community. Comparing functional trait-based niches is extremely useful in theoretical studies of plant ecological strategies, community assembly, and the geographic differentiation of biomes across different climatic zones. Here, data for 11 functional traits belonging to three fundamental niche dimensions (leaf economy, mechanical support, and reproductive phenology) were compiled for 215 woody species from forests across four climatic zones (tropical, subtropical, warm-temperate, and cold-temperate). We constructed the periodic table of niches based on the functional traits of plants in different communities and explored their variations among biomes. A principal component analysis (PCA) was performed to derive the dominant gradients of trait combinations for each individual niche dimensional dataset. Then species scores for the first two axes (PC1 and PC2) were used as inputs for a second PCA to ordinate species in the continuous niche space constrained by the three niche dimensions. Changes in the functional niches of plants from the four biomes along the PC1 and PC2 of niche space were examined based on species scores. Leaf economy was the dominant functional dimension in the plant niche space, followed by mechanical support. Considerable niche convergences among different species were found in the niche space for each biome, except cold-temperate forest. The species niches varied mainly with the increasing specific leaf area/decreasing stem tissue density along PC1, and with the decrease of leaf area/plant size along PC2 from tropical to temperate forests, suggesting that the ecological strategies of plants in the four biomes changed from conservative to acquisitive with an increase in latitude. Our results confirmed that the periodic table of niches does exist and can be constructed by major functional dimensions composed of dominant functional traits. The periodic table of niches effectively reflects the changes of ecological strategies of plant species in biomes across different climatic zones.

Impacts of Decommissioning and Upgrading Urban Wastewater Treatment Plants on the Water Quality in a Shellfish Farming Coastal Lagoon (Ria Formosa, South Portugal)

Jacob, J.; Correia, C.; Torres, A.F.; Xufre, G.; Matos, A.; Ferreira, C.; Reis, M.P.; Caetano, S.; Freitas, C.S.; Barbosa, A.B., and Cravo, A., 2020. Impacts of decommissioning and upgrading urban wastewater treatment plants on the water quality in a shellfish farming coastal lagoon (Ria Formosa, South Portugal). In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 45–50. Coconut Creek (Florida), ISSN 0749-0208.Ria Formosa is a productive coastal lagoon, located on the south coast of Portugal, and represents the largest national producer of shellfish bivalves (ca. 90% production). This ecosystem is subjected to various anthropogenic pressures, including the discharge of urban wastewater treatment plants (UWWTP), which impacts the lagoon water quality. This study aimed to assess the impact of alterations in the functioning of two UWWTP on the water quality of Ria Formosa, based on chemical variables, phytoplankton composition (including potential harmful species) and faecal contamination. During the period September 2018 - October 2019, water sampling was conducted along dominant longitudinal gradients of the effluent dispersion from the discharge point (1-2 km), for two sites: a decommissioned (OP) and a modified (FO) UWWTP. After modification, the later started receiving a higher influent volume (ca. 40%), under an innovative technology system (biological treatment in aerobic granular sludge). Based on chemical water quality variables, phytoplankton and indicators of faecal contamination, a significant improvement along the longitudinal gradient from the discharge point was observed after OP decommissioning. This improvement was fast, being detected two months after decommissioning, positively affecting areas used as shellfish farming grounds. However, distribution patterns of bacteriological indicators and regular shellfish harvesting interdictions suggested an alternative source of faecal contamination after OP decommissioning. At FO, both chemical variables and bacteriological indicators of faecal contamination revealed a slower improvement, only six-months after the UWWTP alteration. Before that, increased and highly variable ammonium, chlorophyll a concentration, phytoplankton abundances and Escherichia coli densities, revealed an unstable phase. Overall, a lower water quality at FO in respect to OP reflected not only a higher effluent volume but also more restricted water circulation for the former.

The thalamic functional gradient and its relationship to structural basis and cognitive relevance

The human thalamus is an integrative hub richly connected with cortical networks, involving diverse cognitive functions. Emerging evidence suggests that multiscale structural and functional gradients integrate various information across modalities into an abstract representation. However, the presence of functional gradients in the thalamus and its relationship to structural properties and cognitive functions remain unknown. We estimated the functional gradients of the thalamus in two independent normal cohorts using a novel diffusion embedding analysis. We identified two main axes of the functional connectivity patterns, and examined associations with thalamic anatomy, morphology, intrinsic geometry, and specific behavioral relevance. We found that the dominant gradient indicated a lateral/medial axis across the thalamus and captured associations with anatomical nuclei and gray matter volume. The second gradient was an anterior/posterior axis and provided a behavioral characterization from lower level perception to higher level cognition. Furthermore, these two gradients strongly correlated with spatial distance, indicating the prominence of intrinsic geometry in functional hierarchies. These findings were replicated in an independent dataset. Overall, our findings suggested that macroscale gradients showed a coordination of structural and functional interactions, with hierarchical organization contributing to behavior characterization.

Does recent climate warming drive spatiotemporal shifts in functioning of high-elevation hydrological systems?

Reference evapotranspiration (ETo) is the basic component of the hydrological cycle. This study systematically analyzed the spatiotemporal variations of ETo in the Three-River Headwaters Region (TRHR) by utilizing the FAO Penman–Monteith equation during the period of 1961–2016, and studied the impact of climatic variables on ETo fluctuation based on sensitivity analysis and contribution analysis. Over the past 56 years, ETo increased in most months and annually in most regions of the TRHR, and the spatial distribution for annual ETo varied apparently. Sensitivity analysis revealed that ETo responded more to changes in maximum temperature and sunshine duration than relative humidity, wind speed, and minimum temperature. The relative importance of climatic variables to ETo was influenced by the ETo sensitivity and the fluctuation of climatic variables. Contribution analysis indicated that the significant temperature increase was mainly responsible for the observed increase in ETo. Besides, spatially distributed analysis showed that the annual TRHR ETo tended to increase from east to west, north to south, and high to low elevation. The analysis also indicated a dominant altitudinal spatial gradient in the sensitivity of ETo to changes in different climatic variables. The physical mechanisms for ETo variations discussed in this study might provide a reference for water resources management and conservation of high-elevation areas.

Forestland-peatland hydrologic connectivity in water-limited environments: hydraulic gradients often oppose topography

It is common to conceptualize the water table as a subdued replica of surface topography, where groundwater recharges at, and flows from, topographic highs and flows to, and discharges at, topographic lows, in humid (i.e. wetter) environments. This concept is also regularly applied to peatland hydrology, where hydraulic gradients are shown to be towards the peatland. However, this may not be a realistic representation of hydrology for low-relief and sub-humid regions. While it is widely accepted that peatlands maintain internal water tables in drought conditions through a system of autogenic negative feedback loops, there is a general lack of knowledge concerning the controls on, and patterns of, forestland hydrologic process that drive the hydraulic gradients between wetlands and their adjacent forestlands in water-limited conditions in low-relief areas. This study identifies the hydrologic function (i.e. source or sink of water) of forested uplands and peatlands in the Boreal Plains region of Canada and demonstrates that during a mesic (non-drought) year most peatlands are, in fact, potential sources of groundwater to adjacent forestlands. Sixteen forestland-peatland pairs were selected to represent a spectrum of forested hummock and peatland morphometries, topographic positions, and geologic settings. Hydraulic gradients determined for each well pair during the ice-off season demonstrate that the dominant gradient under mesic climatic conditions is from peatlands to adjacent forestlands, opposite of the topographic gradient, and that the sink-source function of each land unit does not change seasonally. Water table depressions under each forested hummock indicate that boreal forestlands are not reliable sources of groundwater recharge, spatially or temporally, which supports previous research showing that peatlands are the primary water source for runoff; illustrating the need for alternative conceptualizations of catchment hydrology in water limited regions of the boreal. Social Media Summary. Forests are poor sources of water to boreal peatlands and landscapes due to water table depressions.

Larger size and older age confer competitive advantage: dominance hierarchy within European vulture guild

Competition for limiting natural resources generates complex networks of relationships between individuals, both at the intra- and interspecific levels, establishing hierarchical scenarios among different population groups. Within obligate scavengers, and especially in vultures, the coevolutionary mechanisms operating during carrion exploitation are highly specialized and determined in part by agonistic behavior resulting in intra-guild hierarchies. This paper revisits the behavioral and hierarchical organization within the guild of European vultures, on the basis of their agonistic activities during carrion exploitation. We used a dataset distilled from high-quality videorecordings of competitive interactions among the four European vulture species during feeding events. We found a despotic dominance gradient from the larger species to smaller ones, and from the adults to subadults and juveniles, following an age and body size-based linear pattern. The four studied species, and to some extent age classes, show despotic dominance and organization of their guild exerting differential selection to different parts of the carrion. The abundance of these parts could ultimately condition the level of agonistic interactions. We discuss the behavioral organization and the relationship of hierarchies according to the feeding behavior and prey selection, by comparing with other scavenger guilds.

Experimental study of secondary flows above rough and flat interfaces in horizontal gas-liquid pipe flow

We perform an experimental analysis of stratified, co-current gas-liquid flow in a straight pipe, with the aim of investigating secondary flow structures in the gas-phase. Planar PIV (particle image velocimetry) of the pipe centerline as well as stereoscopic PIV of the pipe cross section is performed, considering cases where the interface is either rough (wavy) or flat. Results demonstrate that the interface morphology determines the direction of the secondary flow patterns. Over a flat interface, the secondary flow cells are directed up along the pipe centerline and down along the pipe walls. When the interface is rough (wavy), the direction of the secondary flow cells is reversed. Normalized by the peak axial velocity, the vertical velocity profile in the pipe centerline is seen to collapse to a common curve when the interface is flat, while results indicate that the normalized strength of the secondary flows increase with increasing surface roughness. An assessment of the Reynolds stresses in the cross section is performed, and the direction of the secondary flow cells are found to be well predicted by the dominant gradients of the radial and circumferential Reynolds stresses (τrr and τθθ) in the radial and circumferential direction respectively.

Urbanization effects on sandy beach macrofauna along an estuarine gradient

Abstract The rapid urban population growth and coastal infrastructure development worldwide add dimensionality and complexity to the management process in sandy shores, and therefore the development of beach quality indices that take into account the increasing role of urbanization are particularly relevant. This work analyses the potential of human population density (HPD), nighttime lights and vegetation cover as indicators of urban impact on sandy beach biodiversity. Each indicator was tested against a large-scale 2-yr study of macrofaunal richness and physical characteristics along a strong environmental gradient defined by the widest estuary of the world, the Rio de la Plata. A negative linear relationship between HPD and the number of species was found. The amount of light recorded at night peaked at the most urbanized area in the coast, Montevideo city, and showed a negative relationship with macrofaunal richness. Vegetation cover, expressed through a normalized difference vegetation index, showed a weak positive relationship with species richness. Multiple linear regressions, combining urban indicators and physical characteristics as explanatory variables of macrofaunal richness, showed the best results when HPD and salinity range were combined. A regression tree explained 65% of deviance and had a structure coherent with previous results. Salinity was the dominant ecological driver: beaches with salinity ≥27.2 showed higher species richness, while beaches with less salinity and higher nighttime lights showed the lowest species richness. Random Forests selected salinity (mean and range) and HPD as the most informative variables to discriminate groups of beaches according to their macrobenthic richness. These results reflect that the salinity gradient is a macroscale driver that shapes species richness patterns along this coast, whereas the effects of urbanization are confined within the dominant large-scale environmental gradient. The identification of suitable urban indicators provided in this work constitutes the first step onto the development of more rigorous approaches to assess this globally relevant and long-lasting stressor.

Responses of soil bacterial compositions to concentrations of nitrogen forms in the process of Moso bamboo invasion

AbstractWe analyzed and compared the soil bacterial diversity and difference in community composition in a Moso bamboo forest, a mixed Moso bamboo–conifer (Pinus massoniana) forest, and a coniferous forest. The relative abundances of Acidobacteria and Planctomycetes were significantly lower in the Moso bamboo forest, while those of Actinobacteria, Bacteroidetes, TM‐7 and Chlamydiae were greatly increased. The α‐diversity in the Moso bamboo forest was different from that in the other two forest types but was not statistically distinguished. Principal coordinates analysis suggested that the invasion of Moso bamboo affected the community composition and diversity of soil bacteria. This impact was associated with the soil biochemical environment, as evidenced by increased mean values of soil organic carbon (C) and total nitrogen (N), significant increases in microbial biomass C and N, and a decrease in the NO3−–N content, which indicated that the nitrification rate was reduced in the mixed Moso bamboo–conifer forest. There were no overall correlations between the dominant bacterial phyla and soil biochemical gradients; however, individual dominant phyla correlated with the concentration of N forms, which indicated that the responses of bacteria were sensitive to, and varied depending on, the concentration of soil N forms. In addition, there were correlations between non‐dominant bacterial phyla with respect to operational taxonomic unit proportions <1.0%, and overall gradients of water‐soluble organic N and NO3−–N. The results of this study showed that the changes in soil bacterial flora are associated with the changes in concentration of N forms during the invasion of Moso bamboo.

Identifying the mechanisms that shape fungal community and metacommunity patterns in Yunnan, China

Abstract Fungi are key organisms in terrestrial ecosystems, functioning as decomposers, pathogens, and symbionts. Identifying the mechanisms that shape metacommunity patterns is likely to be critical for predicting how ecosystems will respond to global environmental change. Using fungal occurrence data and a hierarchical approach that combines three elements of metacommunity structure—coherence, turnover and boundary clumping—we identified the structures that best describe metacommunity patterns. We related these patterns to underlying environmental and spatial variables known to influence fungal distribution, and determined the relative importance of the environment and geographic distance in structuring fungal metacommunities. Fungal metacommunities had Clementsian and quasi-Clementsian structures, indicating that species distributions were compartmentalized along a dominant environmental gradient. This gradient was strongly associated with annual precipitation, precipitation seasonality and pH for the entire metacommunity. Variance partitioning revealed that the environment was relatively more important than geographic distance in explaining metacommunity patterns, indicating that niche-based processes are crucial in shaping species distributions among sites. However, the strength of the relationship between the latent gradient and environmental factors and the relative contributions of the environment and geographic distance to metacommunity structure varied across groups, suggesting that interactions among habitat, dispersal and life-history might be driving these differences.

Microstructure and grain growth direction of SRR99 single-crystal superalloy by selective laser melting

Nickel-based Single Crystal (SX) superalloys have an excellent creep ductility and thermal fatigue resistance at elevated temperatures. But SX structure is difficult to be manufactured under the demand of increasing operating temperature and complex shapes. In this work, the feasibility of manufacturing Nickel-based SX-superalloys by selective laser melting (SLM) was investigated theoretically and experimentally. Firstly, the solidification conditions including temperature field, thermal gradient and solidification speed of the SLMed multi-track samples were calculated by an established finite element model to judge the theoretical feasibility based on the columnar to equiaxed transition (CET). Then, the single-track, triple-track and cuboid samples on a single-crystal SRR99 substrate were deposited to judge the experimental feasibility and explore their grain growth mechanism during SLM. The results showed that CET can be avoided during the whole process of SLM. The unidirectional SRR99 SX structure with a height of 2 mm can be successfully obtained by SLM. On horizontal section, the microstructures can be divided into [001] orientation zone, [010] orientation zone and overlapping zone with a typical secondary dendrite structure. On vertical section, the columnar dendritic structure along the dominant thermal gradient direction is present. The primary dendrite spacing of the SLMed samples (∼1–2 μm) is more than two orders of magnitude lower than that of the cast one (∼320 μm). So, SLM technology possesses the capacity to manufacture SX superalloy. When the deposited height reaches 6 mm, the misorientation angle is about 25° and a crack initiates. Finally, the grain growth mechanism of the SLMed SRR99 single-crystal superalloy was proposed based on the local thermal gradient, the existing well-aligned crystallographic orientation and the preferential grain growth direction.

Gradient structural similarity based gradient filtering for multi-modal image fusion

In the conventional structure tensor-based gradient domain image fusion methods, a structure tensor is exploited to calculate the fused gradient, from which the fused image can be derived using a variational model. However, in these conventional methods, because the direction of fused gradient at every position is determined by the inner product between the average of multiple source gradients and the biggest eigenvalue of structure tensor, its accuracy would be suffered by the canceling effect in calculating the average source gradient. To address such issue, we propose a novel local structural similarity metric to determine the dominant source gradient and correct the direction of fused gradient by the inner product between the biggest eigenvalue of structure tensor and the dominant source gradient. Moreover, in order to highlight salient features of the source images with the dominant source gradients, we propose a structural similarity based gradient filtering scheme which simultaneously performs filtering and fusion on both the source gradients and the corrected fused gradients to obtain the final fused gradients. Finally, the fused image can be reconstructed from the final fused gradients using a variational model like the conventional structure tensor-based fusion schemes. The comprehensive experiment results have revealed that our image fusion method can obtain better objective and subjective fusion performances compared to the state-of-the-art image fusion methods.

Inter-regional beta-diversity patterns of the woody flora of Greece

This study aimed to estimate and explain the compositional differentiation and observed beta-diversity (partitioned as turnover and nestedness) patterns of woody species in Greece. Specifically, the 13 phytogeographical regions of Greece were compared at three taxonomic levels: family, genus, and (sub-) species. In Greece, 565 woody taxa have been identified, which are classified into 224 genera and 85 families. Phytogeographical regions were grouped according to their similarity in floristic composition using cluster analysis. Dominant beta diversity gradients were detected using Mantel directional correlation tests applied at the three taxonomic levels. The 13 phytogeographical regions formed three groups; namely, the northern, central, and southern (Aegean Islands) regions. The taxonomic variation among the phytogeographical regions at the species level was related to a gradient of richness of widespread taxa and Balkan endemic taxa. Analysis at the taxonomic levels of species and genus produced similar results, yet, at the family level, floristic differences were less pronounced, with phytogeographical regions being aggregated in two groups: the southernmost island regions versus all other regions. Beta diversity was higher along a northwestern to southeastern gradient, which was related to a dominant climatic gradient throughout Greece. The partitioning of beta diversity between neighboring phytogeographical regions showed that species turnover was the dominant component; yet, some phytogeographical regions (e.g., Kiklades) were characterized by high nestedness. In conclusion, analysis of woody taxa provides different insights regarding the floristic variation of phytogeographical regions.

In-silico study of the ionic current gradients determining left-to-right atrial frequencies during paroxysmal atrial fibrillation

Atrial fibrillation is the most prevalent cardiac arrhythmia. Paroxysmal atrial fibrillation (pAF) may occur in episodes lasting from minutes to days. Recent studies suggest that some pAF episodes present a left-to-right dominant frequency gradient caused by ionic current gradients. However, how each ionic current gradient affects the left-to-right dominant frequency gradient during pAF has not been studied. In this work, we use a 3D model of human atria to study how the ionic current gradients affect the dominant frequency gradient during pAF induced by continuous ectopic activity. The role of the specific gradients of acetylcholine-activated potassium current ( IKACh) and inward-rectifier potassium current ( IK1) on determining the left-to-right dominant frequency gradient was assessed. The main outcome of this study is that either or both of the IKACh or IK1 gradients are necessary to induce a left-to-right dominant frequency gradient during pAF. However, both gradients are necessary to the left atrium maintaining, by itself, the pAF episode. These findings have potentially important implications for the development of atrial-selective therapeutic approaches.

Robust Semantic Template Matching Using A Superpixel Region Binary Descriptor.

Almost all conventional template-matching methods employ low-level image features to measure the similarity between a template image and a scene image using similarity measures such as pixel intensity and pixel gradient. Although these methods have been widely used in many applications, they cannot simultaneously address all types of robustness challenges. In this study, with the goal of simultaneously addressing the various challenges, we present a robust semantic template-matching approach (RSTM). Inspired by the local binary descriptor, we propose a novel superpixel region binary descriptor (SRBD) to construct a multilevel semantic fusion feature vector for RSTM. SRBD uses a new kernel-distance-based simple linear iterative clustering (KD-SLIC) method to extract the stable superpixels from the template image; Then, based on the average intensity difference between each superpixel region and its neighbors, the dominant gradient orientation of each superpixel can be obtained, and the semantic features of each superpixel can be described as the dominant orientation difference vector, which is coded as the rotation-invariant SRBD. In the off-line matching phase, the fusion semantic feature vector of RSTM combines the multilevel SRBD features with different numbers of superpixels. In the online matching phase, to cope with rotation invariance, a marginal probability model is proposed and applied to locate the positions of template images in the scene image. Moreover, to accelerate computation, an image pyramid is employed. We conduct a series of experiments on a large dataset randomly selected from the MS COCO dataset to fully analyze the robustness of this approach. The experimental results show that RSTM simultaneously addresses rotation changes, scale changes, noise, occlusions, blur, nonlinear illumination changes and deformation with high time efficiency while also outperforming previous stateof- the-art template-matching methods.

Accounting for intraspecific diversity when examining relationships between non-native species and functional diversity.

Quantifying changes in functional diversity, the facet of biodiversity accounting for the biological features of organisms, has been advocated as one of the most integrative ways to unravel how communities are affected by human-induced perturbations. The present study assessed how functional diversity patterns varied among communities that differed in the degree to which non-native species dominated the community in temperate lake fish communities and whether accounting for intraspecific functional variability could provide a better understanding of the variation of functional diversity across communities. Four functional diversity indices were computed for 18 temperate lake fish communities along a gradient of non-native fish dominance using morphological functional traits assessed for each life-stage within each species. First, we showed that intraspecific variability in functional traits was high and comparable to interspecific variability. Second, we found that non-native fish were functionally distinct from native fish. Finally, we demonstrated that there was a significant relationship between functional diversity and the degree to which non-native fish currently dominated the community and that this association could be better detected when accounting for intraspecific functional variability. These findings highlighted the importance of incorporating intraspecific variability to better quantify the variation of functional diversity patterns in communities facing human-induced perturbations.

Microstructure simulations of Inconel 718 during selective laser melting using a phase field model

In this study, the microstructure evolution of the Inconel 718 alloy fabricated by selective laser melting (SLM) was investigated by a phase field model. The temperature gradient and the solidification velocity were first calculated from a finite element thermal model of SLM and then used as the input of the phase field model to simulate the microstructure growth with time. The influences of the build height and laser beam scanning speed on the microstructure evolution were studied and evaluated. The results show that the columnar dendritic arm spacing values estimated from the phase field simulations are comparable to experimental and analytical results. With the increase of the build height, the dominated values of thermal gradient and cooling rate decreased first and then slightly increased at the top end of the manufacturing process. The microstructural evolution along the build height agreed well with the experimental test. In addition, with the increase of the laser beam scanning speed, the dominant temperature gradient increased to a certain value and then decreased, and the direction of the maximum temperature gradient tended to be parallel to the part build direction. Moreover, the temperature gradient affects the dendrite growth significantly, a greater temperature gradient resulting in a higher growth speed.

Plant dominance in a subalpine montane meadow: biotic vs. abiotic controls of subordinate diversity within and across sites.

BackgroundUnderstanding the underlying factors that determine the relative abundance of plant species is critical to predict both biodiversity and ecosystem function. Biotic and abiotic factors can shape the distribution and the relative abundance of species across natural communities, greatly influencing local biodiversity.MethodsUsing a combination of an observational study and a five-year plant removal experiment we: (1) documented how plant diversity and composition of montane meadow assemblages vary along a plant dominance gradient using an observational study; (2) tracked above- and belowground functional traits of co-dominant plant species Potentilla and Festuca along a plant dominance gradient in an observational study; (3) determined whether plant species diversity and composition was directly influenced by commonly occurring species Potentilla and Festuca with the use of a randomized plot design, 5-year plant removal experiment (no removal control, Potentilla removed, Festuca removed, n = 10).ResultsWe found that subordinate species diversity and compositional dissimilarity were greatest in Potentilla and Festuca co-dominated sites, where neither Potentilla nor Festuca dominated, rather than at sites where either species became dominant. Further, while above- and belowground plant functional traits varied along a dominance gradient, they did so in a way that inconsistently predicted plant species relative abundance. Also, neither variation in plant functional traits of Festuca and Potentilla nor variation in resources and conditions (such as soil nitrogen and temperature) explained our subordinate diversity patterns. Finally, neither Potentilla nor Festuca influenced subordinate diversity or composition when we directly tested for their impacts in a plant removal experiment.DiscussionTaken together, patterns of subordinate diversity and composition were likely driven by abiotic factors rather than biotic interactions. As a result, the role of abiotic factors influencing local-level species interactions can be just as important as biotic interactions themselves in structuring plant communities.

A bi-planar coil system for nulling background magnetic fields in scalp mounted magnetoencephalography

Small, commercially-available Optically Pumped Magnetometers (OPMs) can be used to construct a wearable Magnetoencephalography (MEG) system that allows large head movements to be made during recording. The small dynamic range of these sensors however means that movement in the residual static magnetic field found inside typical Magnetically Shielded Rooms (MSRs) can saturate the sensor outputs, rendering the data unusable. This problem can be ameliorated by using a set of electromagnetic coils to attenuate the spatially-varying remnant field. Here, an array of bi-planar coils, which produce an open and accessible scanning environment, was designed and constructed. The coils were designed using a harmonic minimisation method previously used for gradient coil design in Magnetic Resonance Imaging (MRI). Six coils were constructed to null Bx, By and Bz as well as the three dominant field gradients dBx/dz, dBy/dz and dBz/dz. The coils produce homogeneous (within ±5%) fields or field gradients over a volume of 40 × 40 × 40 cm3. This volume is sufficient to contain an array of OPMs, mounted in a 3D-printed scanner-cast, during basic and natural movements. Automated control of the coils using reference sensor measurements allows reduction of the largest component of the static field (Bx) from 21.8 ± 0.2 nT to 0.47 ± 0.08 nT. The largest gradient (dBx/dz) was reduced from 7.4 nT/m to 0.55 nT/m. High precision optical tracking allowed experiments involving controlled and measured head movements, which revealed that a rotation of the scanner-cast by ±34° and translation of ±9.7 cm of the OPMs in this field generated only a 1 nT magnetic field variation across the OPM array, when field nulling was applied. This variation could be further reduced to 0.04 nT by linear regression of field variations that were correlated with the measured motion parameters. To demonstrate the effectiveness of the bi-planar coil field cancellation system in a real MEG experiment, a novel measurement of retinotopy was investigated, where the stimulus remains fixed and head movements made by the subject shift the visual presentation to the lower left or right quadrants of the field of view. Left and right visual field stimulation produced the expected responses in the opposing hemisphere. This simple demonstration shows that the bi-planar coil system allows accurate OPM-MEG recordings to be made on an unrestrained subject.