1,721,112 research outputs found
The legacy of plant invasions: changes in the soil seed bank of invaded plant communities
No full textAssessing the legacy of plant invasions on resident plant communities requires a thorough understanding of changes occurring in the above-ground vegetation as well as in the soil seed bank. Since seed banks represent a memory of past and present vegetation and largely regulate the regenerative potential of species reproducing by seed, knowledge of the impact of plant invasions on the seed bank is essential to predict future population and community dynamics. Here, we review this knowledge and how it may contribute to understanding the relationship between the seed bank and the above-ground vegetation. We discuss how changes in the seed bank may be a symptom of habitat degradation, reducing the resistance of resident communities to primary invasions, and/or a driver promoting secondary invasions. Finally, we describe some of the major issues characterizing seed bank studies in invasion ecology and outline the most promising research directions
Common market, shared problems: time for a coordinated response to biological invasions in Europe
No full textCompetitive balance between the alien invasive Acacia longifolia and native Mediterranean species
No full textWerner C, Peperkorn R, Maguas C, Beyschlag W. Competitive balance between the alien invasive Acacia longifolia and native Mediterranean species. In: Tokarska-Guzik B, Brock J, Brundu J, Child L, Daehler C, Pysek P, eds. Plant Invasions: Human perception, ecological impacts and management. Leiden, The Netherlands: Backhuys Publishers; 2008: 261-275
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
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
Phylogenetic relatedness mediates persistence and density of soil seed banks
No full textSoil seed banks can strongly affect survival and expansion of plant populations by spreading mortality risks and distributing genetic diversity through time. Knowledge of the main factors regulating the ability of seeds to persist in the soil beyond the first germination season is however limited. While morphological and physiological seed traits, and the degree of environmental uncertainty are considered important in shaping the seed banking strategies of plants, global assessments that explicitly account for phylogenetic relatedness are lacking. Using a global seed bank database comprising data for 2,350 angiosperms, we examined the extent to which two seed bank properties, i.e. seed bank type (transient vs. persistent) and density of viable seed banks, are determined by phylogenetic relatedness. We then tested phylogenetic correlations between these properties with seed mass and seed dormancy (dormant vs. non-dormant), and the contribution of phylogenetic relatedness relative to that of climatic and habitat-related variables in shaping seed bank properties. We found significant phylogenetic signal in seed bank type and density, providing evidence that the ability to form persistent seed banks is not randomly distributed across the phylogeny. While the ability to persist in the soil was phylogenetically correlated to the production of dormant and smaller seeds, seed mass and seed dormancy per se were poor predictors of seed persistence. Interestingly, habitat-related variables (mainly disturbance and canopy openness) but not climate significantly affect the ability of seed plants to form persistent seed banks. Synthesis. Our study is the first to show that phylogenetic relatedness plays an important role in explaining seed bank properties in angiosperms and how these properties relate to early life-history traits, climate and habitat-related variables. These findings represent a starting point to assess the generality of persistent seed banks as a bet-hedging strategy in unpredictable environments and provide important insights into how seed plants might respond to global environmental changes
A methodological approach for mapping alien plants in Sardinia (Italy)
No full textIn this paper we analyse and discuss the methodology used for the first project of mapping a set of 109 alien species of the alien flora of Sardinia (Italy). This project, funded by the Nature Conservation Service of the Italian Ministry of the Environment, started in 2000 and ended in December 2002. It has highlighted peculiar problems and stimulated the search for possible methodological solutions. This strategy is of national concern, because the island of Sardinia is a pilot study area for a mapping project methodology that may be extended to other Italian regions. In this paper we focus on project data and metadata definitions, sets of mapped aliens, geocoding of data, GPS surveys, GIS-oriented field surveys and features, chosen between raster and vector analysis. The presence of alien species, according to previous studies ranges from 70 to 184 species. We present and discuss some preliminary results of the mapping of a set of 109 species selected from a set of ca. 900. They have been mapped over the whole island according to a 10 x 10 km grid (3 10 cells), taking into account the topology of the community, cover, habitat and land use of the invaded site. By 2002, we had located a network of 12,065 GPS locations, which included 3,485 sites where none of the given aliens had been found at the time of the survey. Alien distribution in the island has been ranked in eight empirical classes according to the total number of records, the number occupied cells and other features. Some species, e.g. Opuntia ficus-indica, have been recorded in so many sites (> 1,000) and are present in so many 200 cells (> 200), that it can be defined a landscape alien, due to the great visual impact on the landscape all around the island. The project has highlighted the feasibility of the described and used methodology, the underestimated values given to the Sardinian alien flora by previous studies and the uneven distribution of most of the 109 mapped species at the Regional scale. Most of the aliens occur at higher frequencies close to the main settlements of Sardinia, along road and riparian networks, in irrigated agricultural areas, along the coastline and at lower altitudes, in natural and semi-natural habitats. Future monitoring and further studies will constitute a first priority, as the importance and abundance of the Sardinian alien flora has been clearly shown by this study
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