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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
Evolutionary imbalance, climate and human history jointly shape the global biogeography of alien plants
No full textHuman activities are causing global biotic redistribution, translocating species and providing them with opportunities to establish populations beyond their native ranges. Species originating from certain global regions, however, are disproportionately represented among naturalized aliens. The evolutionary imbalance hypothesis posits that differences in absolute fitness among biogeographic divisions determine outcomes when biotas mix. Here, we compile data from native and alien distributions for nearly the entire global seed plant flora and find that biogeographic conditions predicted to drive evolutionary imbalance act alongside climate and anthropogenic factors to shape flows of successful aliens among regional biotas. Successful aliens tend to originate from large, biodiverse regions that support abundant populations and where species evolve against a diverse backdrop of competitors and enemies. We also reveal that these same native distribution characteristics are shared among the plants that humans select for cultivation and economic use. In addition to influencing species’ innate potentials as invaders, we therefore suggest that evolutionary imbalance shapes plants’ relationships with humans, impacting which species are translocated beyond their native distributions.publishe
Introduction history mediates naturalization and invasiveness of cultivated plants
Get PDFAimSpecies characteristics and cultivation are both associated with alien plant naturalization and invasiveness. Particular species characteristics are favoured for cultivation, obscuring the relationship between traits and naturalization success. We sought to better understand the drivers of naturalization and invasiveness by analysing relationships with species characteristics and cultivation and by disentangling the direct effects of characteristics from the indirect effects mediated by cultivation.LocationGreat Britain.Time periodc. 1000–present.Major taxa studiedSeed plants.MethodsWe used a comprehensive dataset of 17,396 alien plant taxa introduced to Great Britain before 1850, a country with one of the most well-documented histories of plant introductions. We integrated this with cultivation data from historical and modern records from botanic gardens and commercial nurseries and with trait data. Accounting for time since introduction, we quantified the influences of cultivation and species characteristics on present-day naturalization and invasiveness in Great Britain.ResultsLarger native range size, earlier flowering, long-lived herbaceous growth form, and outdoor cultivated habitat were all associated with naturalization. However, these relationships between characteristics and naturalization largely reflected cultivation patterns. The indirect, mediating influence of cultivation on naturalization varied among species characteristics, and was relatively strong for growth form and weak for native range size. Cultivation variables, particularly availability in present-day nurseries, best explained invasiveness, while species characteristics had weaker associations.Main conclusionsHuman influence on species introduction and cultivation is associated with increased probability of naturalization and invasiveness, and it has measurable indirect effects by biasing the distribution of species characteristics in the pool of introduced species. Accounting for human cultivation preferences is necessary to make ecological interpretations of the effects of species characteristics on invasion.<br/
Uncovering structural features that underlie coexistence in an invaded woody plant community with interaction networks at multiple life stages
No full textUnderstanding the patterns of competitive and facilitative interactions within and among species in plant communities is a central goal of plant ecology, because these patterns determine species coexistence and community dynamics. Network theory provides tools that allow these patterns to be quantified, and can provide greater understanding of important community properties, including community stability, than can documenting pairwise species interactions.
I characterized the interactions of multiple, co-occurring invasive and native species in an old field woody plant community to build plant interaction networks at two different life stages. With the goal of identifying structural features that may operate to maintain species coexistence, I characterized the architecture of these networks at multiple scales: the entire network, the substructures that compose the network, and species' roles within substructures.
I found that species-level pairwise interactions alone did not provide an accurate or sufficiently detailed picture of community structure. Rather, using a network approach, I identified substructures that have the potential to promote and hinder species coexistence in interactions among seedlings. Characterizing the nuances of network substructures was illuminating, as the size of the substructures and the pattern of interaction intensities within substructures influence the expected effects on species coexistence. Including interactions at multiple life stages was also important; the seedling species that benefited most from the nested structure of facilitative interactions with adults occupied subordinate roles in substructures with other seedlings. This role reversal at different life stages is a potential factor promoting coexistence in the community. Last, the network framework was useful for comparing species' roles between native and invasive members of the community, and the three invasive species in this system had different, life-stage dependent strategies in interactions with co-occurring plants.
Synthesis. The interplay of network architecture and substructures within plant communities and among plants at different life stages is important for understanding species coexistence. In the plant community characterized in this study, there were several features that may promote coexistence, and these features were not observable in interactions within a single life stage or when considering pairwise interactions independently.Raw aboveground biomass data (PlantPerformance.csv)
This is a CSV datafile of aboveground biomasses (in g) of target seedlings from seedling-seedling garden experiments (Experiment column "SS") and adult-seedling field experiments (Experiment column "AS"). Target and neighbor species are abbreviated using the first letters of the genus and species names. Entries with "NA" in the Neighbor column are control treatments. This dataset is the only input that needs to be read into the R code files.
R code used to conduct analyses (PlantInteractionNetworkAnalysis.zip)
This zip file contains all R code used to conduct the analyses in this manuscript:
MAIN.R: in this file, packages are loaded and global variables are set. JAGS models and functions are set using sourced files. Sub-files for analyses are sourced.
functions.R: all functions used in the analysis are defined. All analyses files are dependent on this file.
JAGSmodels.R: all JAGS models used in the analysis are defined and written as .jags files. Analysis file "strength.R" is dependent on this file.
RII.R: Relative Interaction Intensities are calculated for all pairwise interactions using aboveground biomass performance data.
strength.R: in- and out-strengths are estimated using JAGS models (depends on JAGSmodels.R).
substructures.R: the frequency of all three- and four-species substructures are calculated for competitive outcomes networks. Species positions and competitive assymetries are also calculated.
substructures_Strict.R: the same analysis as in "substructure.R" but with stricter criteria for competitive outcomes.
nestedness.R: nestedness (wNODA) of the facilitative and competitive interactions is calculated for the adult-seedling network and compared with three null models.
connectance.R: calculate interaction diversity for the seedling-seedling and adult-seedling network and compare with three null models.The raw aboveground biomass data are provided as a .csv file. These data are aboveground biomasses (in g) of target seedlings from seedling-seedling garden experiments and adult-seedling field experiments.
Seeds were germinated in April 2016 after having implemented stratification and scarification treatments as needed. Seedlings were transplanted into the garden and field experiments in May 2016. In the seedling-seedling garden experiment, all intra- and interspecific pairwise interactions between the seven study species were measured using a target-neighbour design, in which a central target plant was surrounded by four evenly spaced neighbouring plants in pots. Study species included species that are invasive in northeast North America: Rosa multiflora, Elaeagnus umbellata, Berberis thunbergii; and species that are native in the region: Rubus occidentalis, Rhus typhina, Cornus racemosa, and Pinus strobus. Control treatments with a central target plant and no neighbours were also planted. The pots were placed outdoors at the field site (Yale-Myers Forest, Connecticut, USA). Pots were watered to field capacity as needed. In the adult-seedling field experiment, seedlings of all target species were planted under the canopy of adult individuals of R. multiflora, E. umbellata, B. thunbergii, R. occidentalis, and P. strobus. Control treatments with no adult individual were also planted. Plants were harvested in September 2016, and harvested aboveground biomass was dried to constant mass at 60°C and weighed.
The R code used to analyze the data is also included in this dataset as a .zip file. Please see the manuscript for more complete details regarding methods
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
Naturalization of ornamental plants in the United States depends on cultivation and historical land cover context
No full textCultivation by humans is the primary mode of introduction for naturalized plants and an important driver of naturalization, a critical step in the invasion process. Historical records of cultivated plants can represent introduced species pools and propagule pressure, allowing for tests of how species' traits and environmental context affect naturalization while accounting for human influence. Ruderal traits, which generally promote naturalization, may not be universally advantageous across closed versus open landscapes (forest versus grassland/shrubland) or different agricultural land use conversion types, though such context dependence has not yet been demonstrated at a broad scale. We analyzed the naturalization of 3949 cultivated ornamental non‐native plant taxa that were for sale in nursery and seed catalogs in the conterminous United States during a period over 200 years to test for context dependence between traits associated with ruderality (short lifespan, shade intolerance, and self‐compatibility) and estimates of historical forest/grassland cover and agricultural land use change. We found that present‐day naturalization was closely tied to longer cultivation duration and greater cultivation extent. While ruderal traits tended to promote naturalization, perennial lifespan and shade tolerance favored naturalization in US states with higher forest cover, which is consistent with an alternative invasion strategy in closed‐canopy systems. Land use conversion to pasture and succession of abandoned agricultural land promoted naturalization of disturbance‐adapted plants in both forest and grassland landscapes. Our results emphasize the central role of cultivation in plant invasion and provide spatially and temporally extensive evidence that, while ruderal traits are important predictors of naturalization, they are dependent on the landscape context into which plants are introduced. Our work demonstrates the importance of integrating historical cultivation and land use/cover data for a nuanced understanding of the ecological factors that drive plant naturalization
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