1,721,064 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Plant traits and their role in determining forest community structure along a soil fertility gradient
No full textPrevious studies have shown that changes in community composition in mature kauri forests are driven by topographical gradients. The extent to which functional traits influence the patterns detected in these forests has not been well-studied. The overall objective of this thesis was to enhance our understanding of what drives community assembly in these forests by testing the importance of functional traits in mediating the relationship between environmental factors and community composition.
Puketī Forest (Northland, New Zealand) was selected as the study site because rapid turnover of species composition occurs over very strong topographic and edaphic gradients. Community composition was determined using forty permanent 400 m² plots that spanned the full gradient in soil properties and topographic variation. Leaf, height and wood traits were measured in thirty of these plots on three individuals (> 10 cm dbh) for each species on each plot. A total of 30 species were studied; the criteria for a species to be included was that the species had to attain a relative abundance of at least 0.05 within a single plot and occur on at least 10 percent of the forty plots sampled. Fully-expanded, mature, healthy, well-lit leaves were collected from the canopy using a pole pruner, shotgun or slingshot. Cores were collected using an increment borer. The relationships between community-weighted mean traits and environmental gradients were analysed using linear regression.
Results showed that there is a continuous compositional change along this environmental gradient and consequently there are few visually abrupt changes that occur between forest types. The exception to this is the kauri-dominated stands that are found in low fertility environments that are present on ridges. Soil variables and topography were found to be correlated, and the environmental variables that explain the majority of the variation in the community composition and functional trait data were soil carbon: nitrogen ratio, total soil phosphorus and soil pH, rather than topography.
Trait – environment regressions showed that traits are filtered along the soil fertility gradient. Species that have high SLA, high leaf and litter nitrogen, low leaf thickness, large seeds and low wood densities were found in the more fertile environments, which have a low soil carbon: nitrogen ratio, high total soil phosphorus and a high pH, such as a gully habitat. At the other end of this gradient, species that have low SLA, low leaf and litter nitrogen, high leaf thickness, small seeds and high wood densities were present in less fertile environments, which have a high soil carbon: nitrogen ratio, low total soil phosphorus and a low pH, such as a ridge top habitat.
Functional diversity indices indicate that the strength of environmental filtering changes along the soil fertility gradient. These indices show that trait variability does vary along the soil fertility gradient and that there are different community assembly processes operating in different places. The strength of the soil fertility as an environmental filter is strongest in low fertility soils, as environmental filtering results in convergence towards traits that confer a resource-retaining strategy.
Previous studies in kauri forests have shown changes in community composition to be determined by topography. This study has shown that these well-known patterns are driven by the filtering of leaf and wood traits along the topographically-driven soil fertility gradient
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Interactions between soil fertility and climate drive variation in functional traits in New Zealand forests.
No full textPlant functional traits provide a mechanistic approach to understanding the processes of environmental filtering and community assembly. Variation along environmental gradients results in changes in the adaptive values of traits. Climate and soil fertility are two dominant factors that drive these patterns of trait variation. These two factors simultaneously select for traits during environmental filtering. However, we do not understand how interactions between climate and soil fertility influence the variation in community-level traits of multiple plant organs. The roles of traits in New Zealand forests are also yet to be studied at a national scale.
This thesis aimed to determine the adaptive values of multiple functional traits across broad climate and soil fertility gradients in New Zealand forests. This was achieved by the following methods. Data were collected for leaf, stem, root, seed, flowering, and whole-plant traits from the 64 most common native trees in forests nationwide. Community composition and soil properties were measured at 324 plots across the country. For each plot, long-term average climate data were extracted from a model. A variable representing variation in soil fertility in the plots was derived by principal components analysis (PCA). Community-weighted mean (CWM) functional traits, i.e. average trait values weighted by the abundance of species, were calculated for each plot. Dimensionality of the specie-trait matrix was determined by PCA. Multiple linear regression was used to model the variation of each of the CWM traits as functions of mean annual temperature (MAT), vapour pressure deficit (VPD), soil fertility, soil fertility × MAT interaction, soil fertility × VPD interaction, total basal area and topography.
Five dimensions of trait variation were identified among New Zealand trees. Soil fertility was a more significant predictor of CWM traits than either of the climate variables. However, both of the interaction effects were significant for most traits and overrode the importance of the main effects. For example, in sites with high fertility soil, leaf economics traits varied from ‘slow’ in cool and dry conditions to ‘fast’ in warm and moist conditions, but in sites with low fertility, these traits were ‘slow’ in all climates. Therefore, the adaptive values of multiple functional traits of New Zealand forests varied depending on both soil fertility and climate.
This thesis provides the first recognition of the significant roles of the interaction effects between soil fertility and climate in driving variation in CWM traits from multiple plant organs. Climate and soil fertility interact in a way that influences CWM trait values independently from the influence of each environmental variable. These interactions are suspected to be important globally and should be tested for worldwide to confirm the generality of their effects. In conclusion, this thesis demonstrates that studying the relationships between CWM traits and soil fertility or climate independently is insufficient, when attempting to understand the process of environmental filtering. It is critical that the interaction effects between climate and soil fertility are included in future studies to enhance our understanding and ability to predict community-level responses to processes such as climate change
Root traits of New Zealand trees: Community-level responses to a soil fertility gradient, and plastic responses to nutrient availability
No full textThe study of plant traits has great application for understanding plant distribution patterns and community assembly at a variety of scales. Roots are a vital component of plant water and nutrient uptake strategy, and yet root traits are not as well understood as leaf or stem traits. In this thesis I aimed to determine the relationships between seedling fine root, leaf, and stem traits of New Zealand tree species, and investigate whether these traits related to species‟ abundance along a soil fertility gradient. I also investigated how seedling traits compare with adult traits, and whether nutrient availability or method of fertiliser application affected seedling trait expression. To achieve these goals, I measured root, leaf, and stem traits on seedlings of 66 native tree species, and combined this with relative abundance data along a strong soil fertility gradient at Puketī forest. I used principle component analysis and ordination to assess the dimensionality of trait variation across species; and linear regressions to compare community-weighted mean (CWM) traits vs. a summarised axis of soil fertility. I also performed regression analysis between seedling traits and adult traits from the literature. To assess the effects of nutrient availability and application I grew four native tree species under three nutrient treatments: low, pulsed, and slow release. I used two-way ANOVA and co-efficient of variation analyses to determine the strength of responses to nutrient treatments.
Dry matter content was positively associated across leaves, roots, and stems, and negatively associated with root nitrogen concentration and relative growth rate, suggesting that at least as seedlings, traits associated with a fast or slow growth strategy are co-ordinated across organs. Root diameter and SRL were independent from this axis of fast-slow growth, suggesting that SRL does not have a direct effect on seedling growth rates and nutrient foraging. A third axis of variation was also identified, strongly influenced by root phosphorus and nitrogen concentrations, but was difficult to interpret. Regression of CWM traits vs. soil fertility showed that traits which comprised the fast-slow PCA axis co-varied strongly with soil fertility. Neither root diameter nor SRL were significantly related to soil fertility, supporting the conclusion that SRL is not adaptive to nutrient foraging ability. Seedling morphology traits are generally well correlated with adults, but tend to be oriented towards a more “acquisitive” growth strategy, suggesting that species may down-regulate their growth over ontogenetic development. The absence of correlation between SRL and soil fertility suggests that alternative root traits may be more applicable for understanding species foraging strategy.
Species‟ responses to the nutrient treatments differed for most traits. Root-to-shoot ratio, growth rate, and root nutrient concentrations responded strongly to nutrient availability, and morphological traits did not respond as strongly. Slow release and pulse treatments were typically similar, and both significantly different to low nutrient treatment. These results suggest that it is practical to compare morphological trait data between studies, provided plants are raised in environments conducive to growth, but that nutrient concentrations and biomass allocation traits can be strongly influenced by soil fertility
Functional trait variation along a hydrological gradient and trait-based predictions of the composition of a wetland plant community
No full textPredicting the assembly of plant communities is considered the Holy Grail of functional ecology and has never been more important as we head into an era of environmental change. Studying plant functional traits provides the best opportunity for understanding the community assembly processes that determine the abundance and distribution of plant species. Plant functional traits provide information on the direct physiological adaptations of plants to various environmental conditions. The assembly of plant communities is driven by filtering processes that select for or against certain functional traits and a plant can only be present within a community if it contains the functional traits necessary to germinate, survive and compete in the environment of the community. An understanding of how functional traits are filtered by the environment and biotic interactions provides the foundations for predictive community assembly models. However, the understanding of how functional traits are filtered along hydrological gradients is poor for the majority of functional traits.
In this thesis I aimed to identify how plant functional traits respond to variation in soil hydrology in the presence and absence of grazing and determine whether a trait-based model of environmental filtering could predict the composition of an ephemeral wetland plant community. To achieve these aims, I performed a survey of the plant community in an ephemeral wetland in grazed and ungrazed transects. The survey was conducted along a hydrological gradient that was split into an elevation gradient above the flood line and a flooding gradient below the flood line. I measured nine root, leaf and shoot traits on 885 plant samples collected during the community survey and investigated the response of community-weighted and individual-level traits along the hydrological gradient using Generalized Additive Models (GAMs) and Generalized Linear Models (GLMs). To determine whether a trait-based model of environmental filtering could predict the composition of the plant community, I incorporated the individual-level trait relationships into a community assembly model known as Traitspace and predicted the relative abundance of the 23 most common species found within the Kettlehole.
Community-weighted root traits were more strongly related to the hydrological gradient than aboveground traits. Root aerenchyma increased as the number of days submerged increased while root dry matter content (RDMC), specific root length (SRL), root tissue density (RTD) and root branching intensity (RBI) decreased with increasing flooding. Community-weighted specific leaf area (SLA) and root tissue density were more closely related to the elevation gradient than any other traits. SLA decreased as elevation above the flood line increased while RTD increased with elevation. The relationships between individual-level traits and the elevation and flooding gradients were far weaker than community-weighted traits but showed similar trends in the directions of trait responses along the gradients. Grazing reduced the community-weighted trait values of all traits except SLA and aboveground dry matter content (AGDMC) along the flooding gradient and had little effect on the trait values observed along the elevation gradient.
Using environmental filtering of functional traits, the Traitspace model was able to predict the distribution and abundance of a number of key species within the wetland plant community but was unable to accurately predict the abundance and distribution of other species. The accuracy of the Traitspace model was best when all nine functional traits were used to produce predictions of species abundances but SLA and height were recognised as the two traits to provide the most predictive ability.
The strong filtering of root traits illustrate the important information that root traits provide in terms of the adaptations of plants in environments with varied soil hydrology. Easily measurable aboveground traits are often favoured in functional ecology but these results highlight the importance of measuring root traits in trait-based research. Traitspace has the ability to predict the abundance and distribution of some species within a wetland plant community using environmental filtering of functional traits. Community assembly at small spatial scales is mostly driven by biotic interactions rather than environmental filtering which may limit the power of current predictive models. The inclusion of biotic interactions into trait-based models will improve the predictions of community composition at small spatial scales in wetland ecosystems and help us to progress towards achieving the goal of accurately predicting the composition of plant communities
Reinforcing loose foundation stones in trait-based plant ecology
No full textThe promise of “trait-based” plant ecology is one of generalized prediction across organizational and spatial scales, independent of taxonomy. This promise is a major reason for the increased popularity of this approach. Here, we argue that some important foundational assumptions of trait-based ecology have not received sufficient empirical evaluation. We identify three such assumptions and, where possible, suggest methods of improvement: (i) traits are functional to the degree that they determine individual fitness, (ii) intraspecific variation in functional traits can be largely ignored, and (iii) functional traits show general predictive relationships to measurable environmental gradients.Shipley, Bill; De Bello, Francesco; Cornelissen, J. Hans C; Laliberté, Etienne; Laughlin, Daniel C; Reich, Peter B. (2016). Reinforcing loose foundation stones in trait-based plant ecology. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/184562
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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