Greater Proportion Of Variation Research Articles

Root-associated fungi and acquisitive root traits facilitate permafrost nitrogen uptake from long-term experimentally warmed tundra.

Root-associated fungi (RAF) and root traits regulate plant acquisition of nitrogen (N), which is limiting to growth in Arctic ecosystems. With anthropogenic warming, a new N source from thawing permafrost has the potential to change vegetation composition and increase productivity, influencing climate feedbacks. Yet, the impact of warming on tundra plant root traits, RAF, and access to permafrost N is uncertain. We investigated the relationships between RAF, species-specific root traits, and uptake of N from the permafrost boundary by tundra plants experimentally warmed for nearly three decades at Toolik Lake, Alaska. Warming increased acquisitive root traits of nonmycorrhizal and mycorrhizal plants. RAF community composition of ericoid (ERM) but not ectomycorrhizal (ECM) shrubs was impacted by warming and correlated with root traits. RAF taxa in the dark septate endophyte, ERM, and ECM guilds strongly correlated with permafrost N uptake for ECM and ERM shrubs. Overall, a greater proportion of variation in permafrost N uptake was related to root traits than RAF. Our findings suggest that warming Arctic ecosystems will result in interactions between roots, RAF, and newly thawed permafrost that may strongly impact feedbacks to the climate system through mechanisms of carbon and N cycling.

Math Attitudes, Engagement, and Performance of High School Students on High and Low-stakes Tests of Statistics Knowledge

Understanding the extent engagement and math attitudes predict performance in statistics courses could inform educational interventions in this subject area, which has growing demand. We examined direct and indirect associations between course engagement-related constructs, math attitudes, and learning outcomes. Confirmatory factor analysis was used to validate scores from measures of these constructs with a sample of high school students enrolled in Advanced Placement (AP) statistics (N = 720, mean age = 16.8 years, SD = 0.82). Structural equation models were fitted to the data to examine relations between these constructs on a subsample (N = 220). A greater proportion of variation was explained in a high-stakes learning outcome (R2 = 0.54) than a low-stakes learning outcome (R2 = 0.24). We found some evidence of indirect effects of academic procrastination and course engagement on the learning outcome by way of math attitudes. The findings shed light on opportunities for intervention on academic maladaptive behaviors, such as procrastination, which could lessen negative effects on math attitudes and learning. These findings highlight the importance of testing stakes when examining associations between engagement, math attitudes, and learning, particularly in the context of high school statistics, a growing and yet understudied STEM learning context.

The relative importance of households as a source of variation in child malnutrition: a multilevel analysis in India

BackgroundChild malnutrition remains a major public health issue in India. Along with myriad upstream and social determinants of these adverse outcomes, recent studies have highlighted regional differences in mean child malnutrition rates. This research helps policy makers look between urban and rural communities and states to take a population-level approach to addressing the root causes of child malnutrition. However, one gap in this between-population approach has been the omission of households as a unit of analysis. Households could represent important sources of variation in child malnutrition within communities, districts, and states.MethodsUsing the fourth round of India’s National Family Health Survey from 2015 to 2016, we analyzed four and five-level multilevel models to estimate the proportion of variation in child malnutrition attributable to states, districts, communities, households, and children.ResultsOverall, we found that of the four levels that children were nested in (households, communities, districts, and states), the greatest proportion of variation in child height-for-age Z score, weight-for-age Z score, weight-for-height Z score, hemoglobin, birthweight, stunting, underweight, wasting, anemia, and low birthweight was attributable to households. Furthermore, we found that when the household level is omitted from models, the variance estimates for communities and children are overestimated.ConclusionsThese findings highlight the importance of households as an important source of clustering and variation in child malnutrition outcomes. As such, policies and interventions should address household-level social determinants, such as asset and social deprivations, in order to prevent poor child growth outcomes among the most vulnerable households in India.

Employing landscape metrics in an open population model to estimate demographic parameters of a grassland bird

The importance of landscape context is increasingly recognized when studying relationships between populations. Recent advances in open population modeling allow the employment of landscape metrics to estimate demographic parameters underlying population variation through time and space. Our primary objectives were to (1) describe the influence of landscape metrics on demographic parameters in the grasshopper sparrow (Ammodramus savannarum) and (2) quantify the contributions of these demographic parameters in influencing variation in territory counts through time. We anticipated results would allow us to make recommendations for prioritizing site conservation for this grassland-obligate species of regional conservation concern. We employed territory counts spanning 13 years from Massachusetts, USA in open population models to estimate the effects of landscape metrics, territory density, and site quality on three demographic parameters. The best model estimated highest initial numbers of territories in larger, more distant sites. Overall growth rates 1 were estimated in larger sites with a higher habitat quality index and low to medium relative density. Highest rates of annual immigration were estimated for larger sites. Growth rate explained the greatest proportion of variation in territory counts through time. Open population models allowed us to identify the effects of landscape context on multiple grasshopper sparrow demographic parameters. We encourage further application of these and related models to grassland birds. Beyond maintaining grasslands in the region, we recommend the conservation of large, distant, and previously occupied sites to benefit regional populations.

High levels of spatial heterogeneity in the biodiversity of soil prokaryotes on Signy Island, Antarctica

In a previous study, soil bacterial diversity at environmentally distinct locations on Signy Island was examined using denaturing gradient gel electrophoresis (DGGE) profiling, and a range of chemical variables in soils was determined in order to describe variations between them. The dominant bacterial communities of all locations were found to be significantly different, although higher levels of similarity were observed between locations with similar physico-chemical characteristics, such as at penguin rookeries, seal wallows and vegetated soils. Extending this study, here soil prokaryote biodiversity was compared between 15 distinct locations in order to elucidate any interaction between four general habitat types on Signy Island (South Orkney Islands, maritime Antarctic) and any influence of previous human impacts at these sites. Specific sites were selected to represent the range of different soil environments present and to cover a range of environmental factors present in the maritime Antarctic which are known to influence bacterial community composition in soils elsewhere. A diverse prokaryote community is described, again with the majority of excised and sequenced bands belonging to the Bacteroidetes. Although DGGE profiling identified significant differences in prokaryotic biodiversity between all sampling sites, aggregations of banding patterns were also apparent across the different soil environments examined. Correlations between specific DGGE profiles and 10 selected soil parameters suggested that much of this variation could be explained by differences in the levels of environmental disturbance and soil pH. In particular, a greater proportion of variation in soil bacterial diversity was explained by differences in soil properties at human-disturbed locations than at undisturbed locations, with higher explanatory values by edaphic factors in the former and soil metal content in the later. In general, our data indicate that small-scale variation is an important factor in understanding patterns of prokaryotic distributions in soil habitats in the maritime Antarctic environment.

Statistical analysis of nitrate concentrations from the Rivers Frome and Piddle (Dorset, UK) for the period 1965–2007

AbstractThe results presented here update those of Casey and Clarke (Freshwater Biology, 1979), ecologists who studied nitrate concentrations in the River Frome in southern England from 1965 to 1976, finding that average annual nitrate concentrations were increasing at the rate of around 0·11 mg NO3N l−1 year−1. Statistical analyses at the same East Stoke site for the period 1978 to 2003 are presented and results are compared with the neighbouring River Piddle for the period 1978 to 2007 which, unlike the Frome, lies entirely within the Chalk in its upper reaches. The method of Casey and Clarke (1979) is followed in applying general linear and nonlinear estimation models (NEMs) to explore the sources of variation in the nitrate concentration data. The proportions of the total variation in nitrate concentration attributable to differences between years and to differences between months are similar for the Frome in both periods. For the Frome and Piddle models from 1978 onwards, an even greater proportion of variation is explained by differences between years rather than differences between months, suggesting that long‐term change is the dominant effect. Analyses of annual mean nitrate concentration data show a sustained linear trend over the study period for both rivers and indicate that the rate of increase of annual mean nitrate concentration continues at a rate not significantly different from that found by Casey and Clarke (1979). Four versions of a NEM were applied, including the original Casey and Clarke (1979) model. The inclusion of flow variables adds little to the overall explanation and a cosine index remains the most effective descriptor of seasonal variations in nitrate concentration, suggesting seasonal in‐stream biological uptake as a dominant control, rather than hydrological catchment response. Copyright © 2008 John Wiley & Sons, Ltd.

Host genotype overrides fungal endophyte infection in influencing tiller and spike production of Lolium perenne (Poaceae) in a common garden experiment

Leaves of many cool-season grasses are infected by endophytic fungi that can impact their populations. A common garden experiment with Lolium perenne was established in a lawn in New Jersey, USA, to investigate the impact of endophyte infection and host genotype on tiller and spike production over three years. Infected (E+) and uninfected (E-) plants of each genotype were monitored every 2-3 mo. Infection intensity within plants varied significantly among genotypes and years, but there was no evidence of directional change over time. Tiller production varied significantly among genotypes and was affected by endophytes: E+ plants of several genotypes produced more tillers than E- plants during the third year. E+ plants had greater aboveground biomass, but host genotype explained a far greater proportion of variation in tiller production, number, and biomass than infection. Plant survival, percentage flowering, flowering date, number of spikes, and mean tiller mass were unaffected by endophytes. However, the last three variables showed significant variation among host genotypes. Although studies have demonstrated a positive growth effect of endophytes on several grass hosts, in this experiment host genotype accounted for far more of the variation in tiller and spike production and in biomass of Lolium perenne than endophyte infection.

Establishing the soundness of administrative spatial units for operationalising the active living potential of residential environments: an exemplar for designing optimal zones

BackgroundIn health and place research, definitions of areas, area characteristics, and health outcomes should ideally be coherent with one another. Yet current approaches for delimiting areas mostly rely on spatial units "of convenience" such as census tracts. These areas may be homogeneous along socioeconomic conditions but heterogeneous along other environmental characteristics. This heterogeneity can lead to biased measurement of environment characteristics and misestimation of area effects on health. The objective of this study was to assess the soundness of census tracts as units of analysis for measuring the active living potential of environments, hypothesised to be associated with walking.ResultsStarting with data at the smallest census area level available, zones homogeneous along three indicators of active living potential, i.e. population density, land use mix, and accessibility to services were designed. Delimitation of zones ensued from statistical clustering of the smallest areas into seven clusters or "types of environment". Mapping of clusters into a GIS led to the delineation of 898 zones characterised by one of seven types of environment, corresponding to different levels of active living potential. Homogeneity of census tracts along indicators of active living potential varied. A greater proportion (83%) of variation in accessibility to services was attributable to differences between census tracts suggesting within-tract homogeneity along this variable. However, census tracts were heterogeneous with respect to population density and land use mix where a greater proportion of the variation was attributable to within-tract differences. About 55% of tracts were characterised by a combination of three or more "types of environment" suggesting substantial within-tract heterogeneity in the active living potential of environments.ConclusionSoundness of census tracts for measuring active living potential may be limited. Measuring active living potential with error may lead to misestimation of associations with walking, therefore limiting the correctness of inference about area effects on walking. Future studies should aim to determine homogeneity of spatial units "of convenience" along environment characteristics of interest prior to examining their association with health. Further evidence is needed to assess the extent of this methodological issue with other indicators of environment context relevant to other health indicators.

EVOLUTIONARY ANALYSIS OF A KEY FLORAL TRAIT IN AQUILEGIA CANADENSIS (RANUNCULACEAE): GENETIC VARIATION IN HERKOGAMY AND ITS EFFECT ON THE MATING SYSTEM

The mating system of flowering plant populations evolves through selection on genetically based phenotypic variation in floral traits. The physical separation of anthers and stigmas within flowers (herkogamy) is expected to be an important target of selection to limit self-fertilization. We investigated the pattern of phenotypic and genetic variation in herkogamy and its effect of self-fertilization in a broad sample of natural populations of Aquilegia canadensis, a species that is highly selfing despite strong inbreeding depression. Within natural populations, plants exhibit substantial phenotypic variation in herkogamy caused primarily by variation in pistil length rather than stamen length. Compared to other floral traits, herkogamy is much more variable and a greater proportion of variation is distributed among rather than within individuals. We tested for a genetic component of this marked phenotypic variation by growing naturally pollinated seed families from five populations in a common greenhouse environment. For three populations, we detected a significant variation in herkogamy among families, and a positive regression between parental herkogamy measured in the field and progeny herkogamy in the greenhouse, suggesting that there is often genetic variation in herkogamy within natural populations. We estimated levels of self-fertilization for groups of flowers that differed in herkogamy and show that, as expected, herkogamy was associated with reduced selfing in 13 of 19 populations. In six of these populations, we performed floral emasculations to show that this decrease in selfing is due to decreased autogamy (within-flower selfing), the mode of selfing that herkogamy should most directly influence. Taken together, these results suggest that increased herkogamy should be selected to reduce the production of low-quality selfed seed. The combination of high selfing and substantial genetic variation for herkogamy in A. canadensis is enigmatic, and reconciling this observation will require a more integrated analysis of how herkogamy influences not only self-fertilization, but also patterns of outcross pollen import and export.