1,721,008 research outputs found
Identifying fine-scale habitat preferences of threatened butterflies using airborne laser scanning
Get PDFAim: Light Detection And Ranging (LiDAR) is a promising remote sensing technique for ecological applications because it can quantify vegetation structure at high resolution over broad spatial extents. Using country-wide airborne laser scanning (ALS) data, we test to what extent fine-scale LiDAR metrics capturing low vegetation, medium-to-high vegetation and landscape-scale habitat structures can explain the habitat preferences of threatened butterflies at a national extent. Location: The Netherlands. Methods: We applied a machine-learning (random forest) algorithm to build species distribution models (SDMs) for grassland and woodland butterflies in wet and dry habitats using various LiDAR metrics and butterfly presence–absence data collected by a national butterfly monitoring scheme. The LiDAR metrics captured vertical vegetation complexity (e.g., height and vegetation density of different strata) and horizontal heterogeneity (e.g., vegetation roughness, microtopography, vegetation openness and woodland edge extent). We assessed the relative variable importance and interpreted response curves of each LiDAR metric for explaining butterfly occurrences. Results: All SDMs showed a good to excellent fit, with woodland butterfly SDMs performing slightly better than those of grassland butterflies. Grassland butterfly occurrences were best explained by landscape-scale habitat structures (e.g., open patches, microtopography) and vegetation height. Woodland butterfly occurrences were mainly determined by vegetation density of medium-to-high vegetation, open patches and woodland edge extent. The importance of metrics generally differed between wet and dry habitats for both grassland and woodland species. Main conclusions: Vertical variability and horizontal heterogeneity of vegetation structure are key determinants of butterfly species distributions, even in low-stature habitats such as grasslands, dunes and heathlands. The information content of low vegetation LiDAR metrics could further be improved with country-wide leaf-on ALS data or surveys from drones and terrestrial laser scanners at specific sites. LiDAR thus offers great potential for predictive habitat distribution modelling and other studies on ecological niches and invertebrate–habitat relationships
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
Of dwarves and giants: How large herbivores shape arthropod communities on salt marshes
Get PDFOm plantensoortenrijkdom te behouden worden op kwelders (buitendijkse graslanden die regelmatig overstromen met zeewater) en veel andere typen natuurgebieden steeds vaker grote grazers, zoals koeien of paarden, ingezet. Hierbij krijgen insecten en andere ongewervelden echter weinig aandacht. Dit proefschrift beschrijft hoe gemeenschappen van ongewervelden reageren op beweiding, met aandacht voor verschillen tussen soorten grazers, beweidingsdichtheden en rotatiebeheer (jaarlijkse wisseling tussen beweide en onbeweide jaren). Plantensoortenrijkdom neemt vaak toe wanneer grote grazers worden ingezet. Dit komt grotendeels omdat deze dieren, door hoge planten op te eten, zorgen dat meer licht de bodem breikt, en lagere planten een kans krijgen. Uit mijn onderzoek blijkt echter dat soortenrijkdom van ongewervelden vaak afneemt in aanwezigheid van grote grazers. Op kwelders zijn de meeste soorten insecten en andere ongewervelden afhankelijk van hoge vegetatie als voedselbron of als bescherming tegen overstromingen, terwijl een minderheid aan soorten korte vegetatie prefereert. Als de vegetatie wordt opgegeten door grote grazers zullen de bestaansmogelijkheden voor de meeste soorten dus afnemen of verdwijnen. Beweidingsdichtheid blijkt voor soortenrijkdom van ongewervelden de belangrijkste bepalende factor te zijn. Dit bepaalt hoe veel vegetatie wordt opgegeten, en dus welke mogelijkheden er voor ongewervelden bestaan. Welke soort grazer wordt ingezet lijkt hier een ondergeschikte rol te spelen. De beste kans om soortenrijkdom van ongewervelden op kwelders en andere typen graslanden te waarborgen ligt in het creeëren van heterogeniteit. Dit kan bereikt worden door verschillend beheerde terreinen naast elkaar te behouden, te beweiden met lage dichtheden of met rotatiebeheer
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
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
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