1,720,980 research outputs found
Phenology of grassland plants responds to urbanization
No full textUnderstanding phenological responses of plants to changing temperatures is important because of multiple associated ecological consequences. Cities with their urban heat island can be used as laboratories to study phenological adaptation to climate change. However, previous phenology studies focused on trees and did not disentangle the role of micro-climate and urban structures.We studied reproductive phenology of dry grassland species in response to micro-climate and urbanization in Berlin, Germany. Phenological stages were recorded weekly at the individual plant level for five native grassland species across 30 dry grassland sites along an urbanization and temperature gradient. We estimated 50% onset probabilities for flowering and seed maturation of populations, and analysed variation in onset dates using regression models.Early flowering species significantly advanced flowering phenology with increasing mean air temperature but were little influenced by urbanization. By contrast, late-flowering species showed significant phenological responses to both air temperature and urbanization, possibly because micro-climate was most affected by urbanization in late summer. Surprisingly, not all grassland species showed an advanced phenology with increasing intensity of urbanization.This contradicts observed patterns for urban trees, indicating that phenological shifts in urban areas cannot be generalized from the observation of one growth form or taxonomic group. Growth form appears as a possible determinant of phenological responses. Results suggest that the phenology of dry grassland species may directly respond to the urban heat island, albeit with variable direction and magnitude. This has implications for ecosystem services, shifted allergy seasons, changes of biogeochemical cycles and potential ecological mismatches
Exploring the biotic homogenization and diversity resistance hypotheses. The understorey of non-native and native woodland canopies in three urban areas of Europe
Get PDFAim: Exploring the biotic homogenization and diversity resistance hypotheses by assessing the effect of non-native black locust canopy on understorey species turnover. Location: Berlin, the Venetian metropolitan area, and Rome. Methods: We modelled the zeta (ζ) expression of diversity to compare the understorey species turnover between the non-native black locust and native woodland canopies across multiple sites and through predictors of anthropogenic pressure (road and built-up density) and interior conditions (tree basal area and mean height). Results: In Rome, black locust showed the lowest survivability and cover and did not produce any homogenization of the understorey. In Berlin and in the Venetian metropolitan area, black locust caused understorey homogenization, although with a lower intensity in Berlin. Under black locust canopies, distance between sites and road density was more consistently associated with species turnover, across urban areas and multiple sites. Under native canopies in Berlin, factors prominently associated with species turnover were road and built-up density and mean tree height, while in the Venetian metropolitan area it was road density. Main conclusions: Evidence in support of the biotic homogenization in contrast to the diversity resistance hypothesis varied across urban areas. Species turnover was influenced by land use patterns more evidently under native tree canopies and where the non-native tree had higher survivability. Similar analyses in other urban areas may confirm these relationships with other types of landscapes
Auswirkungen der Urbanisierung auf gefährdete Pflanzenarten
No full textGiven the rising urban land cover worldwide, the contribution of cities to the conservation of biodiversity becomes increasingly important. Previous research shows that urban environments can host high numbers of species, including endangered plant species. Yet, key questions on the urban contribution to plant conservation remain critically open, as little information is available on how populations of endangered plant species occur across different biotope types within cities and to what extent anthropogenically shaped vs. natural ecosystems provide habitats for endangered plants. This thesis is based on the analysis of a unique dataset with the exact geographical location of 1,742 populations of 213 endangered plant species in the city of Berlin, as well as information on the survival rate of 858 of these populations. Firstly, I assessed the relative importance of Berlin’s major biotope classes as habitats of endangered plant species and applied the novel ecosystem concept to quantify endangered plant populations for natural remnants vs. hybrid vs. novel ecosystems within Berlin. Secondly, I evaluated to which extent these populations of endangered plant species may occur in anthropogenically shaped hybrid or novel ecosystems spatially independently from natural remnants. Finally, I unravelled the most important drivers of population survival of endangered plant species in cities by linking population survival to various parameters (biotope class, patch size, habitat continuity, conservation status, proportion of impervious surfaces, floor space index, human population density, human population constancy, nearby street length, distance to the nearest street, distance to the nearest remnant ecosystem, proportion of nearby forests and grasslands, and plant traits). Results show that populations of endangered plant species were generally, although unevenly, associated with specific biotope classes; with forest, grassland, and ruderal biotopes as the most important habitats. Surprisingly, novel ecosystems harboured the highest numbers of total populations, of total species, and their populations were found to occur independently from natural remnants. Population success was highest in anthropogenically influenced biotopes such as green spaces, built up areas, fields and grasslands as well as in competitive species, while surprisingly it was lowest inside nature protection areas. Quantifying the relative importance of biotope classes and novel vs. (near-)natural ecosystems as habitats of endangered species demonstrates that the urban contribution to biodiversity conservation is best ensured by providing a wide range of ecosystems. Rather than prioritizing only natural remnants, I thus argue for broad approaches to urban biodiversity conservation that include novel ecosystems.Angesichts der weltweit steigenden Landnutzung durch städtische Gebiete wird der Beitrag, den Städte zum Erhalt der Biodiversität leisten können, immer wichtiger. Frühere Untersuchungen haben gezeigt, dass städtische Flächen eine hohe Artenzahl beherbergen können, einschließlich gefährdeter Pflanzenarten. Dennoch bleiben Schlüsselfragen zum Beitrag, den Städte zum Pflanzenartenschutz leisten können, offen, da wenig Informationen darüber vorliegen, wie Populationen gefährdeter Pflanzenarten in verschiedenen Biotoptypen innerhalb der Städte auftreten und inwieweit anthropogen geprägte vs. natürliche Ökosysteme Lebensräume für gefährdete Pflanzen bereitstellen. Die vorliegende Studie verwendet einen einzigartigen Datensatz mit der genauen geographischen Lage von 1.742 Populationen 213 gefährdeter Pflanzenarten in der Stadt Berlin sowie Informationen über die Überlebensrate von 858 dieser Populationen. Zunächst habe ich die relative Bedeutung der großen Berliner Biotopklassen als Lebensraum für bedrohte Pflanzenarten bewertet und das “Novel ecosystem concept” angewendet, um die Eignung von „natural remnants“ vs. „hybrid“ vs. „novel ecosystems“ in Berlin für gefährdete Pflanzenpopulationen zu bestimmen. Zweitens habe ich untersucht, inwieweit diese Populationen gefährdeter Pflanzenarten in anthropogen geprägten „hybrid“ oder „novel ecosystems“ räumlich unabhängig von „remnant ecosystems“ auftreten können. Schließlich ermöglichte die Verknüpfung der Wuchsorte der Populationen mit Parametern auf verschiedenen räumlichen Skalen, die wichtigsten Faktoren für den Populationserfolg zu ermitteln. Die Ergebnisse zeigen, dass Populationen gefährdeter Pflanzenarten im Allgemeinen, wenn auch ungleichmäßig, mit bestimmten Biotopklassen assoziiert waren. Dabei waren Wald-, Grünland- und Ruderalbiotope die wichtigsten Lebensräume. Überraschenderweise beherbergten „novel ecosystems“ die höchste Anzahl von Gesamtpopulationen und Gesamtarten, und ihre Pflanzenpopulationen traten räumlich unabhängig von „natural remants“ auf. Am größten war der Populationserfolg in anthropogen beeinflussten Biotopen wie Grünflächen, bebauten Flächen, Feldern und Grünland sowie bei konkurrierenden Arten, und erstaunlicherweise niedriger innerhalb von Shutzgebieten als außerhalb. Die Ergebnisse zeigen, dass der städtische Beitrag zum Erhalt der Biodiversität am besten durch die Bereitstellung einer vielseitigen Bandbreite an Ökosystemen gewährleistet ist. Anstatt nur Relikte von Naturlandschaften zu priorisieren, plädiere ich für weitreichende Ansätze zum Schutz der städtischen Biodiversität, die auch neuartige Ökosysteme beinhalten
Data from: Plant population success across urban ecosystems – a framework to inform biodiversity conservation in cities
No full text1. In a rapidly urbanising world, the ability of plant species to survive and build self-sustaining populations in urban environments is increasingly important for biodiversity conservation. Yet the contribution of cities to biodiversity conservation remains unclear because ecologists have studied biodiversity patterns, largely without considering the population establishment of plants and the ways in which different kinds of urban ecosystems harbour native and endangered plant species. These limitations can mislead conservation policies for cities.
2. To better-understand how urban ecosystems can contribute to biodiversity conservation, we propose a framework that links the population status (casual or established) of plant species with ecosystem novelty and highlights barriers to population establishment in different types of urban ecosystems, from natural remnants to novel ecosystems.
3. To quantify the relative importance of natural remnants vs. human-shaped ecosystems for the conservation of self-sustaining urban plant populations we re-analyse a unique dataset from a metropolitan region in Europe with information on the population status of 1199 plant species.
4. Results demonstrate that urban ecosystems harbour many established native and endangered species although a considerable share (37%) of species of conservation concern are confined to natural remnants. In hybrid and immature novel ecosystems, high species numbers reflect many species with only casual populations. The role of novel ecosystems as habitats for native and endangered plant species increases as novel ecosystems mature.
5. Synthesis and applications. General information about plant species richness in urban environments may mislead conservation policies as different kinds of urban ecosystems can play different roles in harbouring species of conservation concern. Moreover, presence-absence data can mask establishment failures of species. This proposed framework helps to distinguish between casual and established populations of plant species, and highlights barriers to population persistence in urban ecosystems; reflecting different land uses and land use histories over time. Revealing the role of natural remnants vs. hybrid vs. novel ecosystems as habitats for species of conservation concern illustrates opportunities for biodiversity conservation in all urban ecosystems and can support setting priorities for conservation
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
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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