1,721,012 research outputs found
Alternative Quantifications of Landscape Complementation to Model Gene Flow in Banded Longhorn Beetles [Typocerus v. velutinus (Olivier)]
No full textRapid progression of human socio-economic activities has altered the structure and function of natural landscapes. Species that rely on multiple, complementary habitat types (i.e., landscape complementation) to complete their life cycle may be especially at risk. However, such landscape complementation has received little attention in the context of landscape connectivity modeling. A previous study on flower longhorn beetles (Cerambycidae: Lepturinae) integrated landscape complementation into a continuous habitat suitability 'surface', which was then used to quantify landscape connectivity between pairs of sampling sites using gradient-surface metrics. This connectivity model was validated with molecular genetic data collected for the banded longhorn beetle (Typocerus v. velutinus) in Indiana, United States. However, this approach has not been compared to alternative models in a landscape genetics context. Here, we used a discrete land use/land cover map to calculate landscape metrics related to landscape complementation based on a patch mosaic model (PMM) as an alternative to the previously published, continuous habitat suitability model (HSM). We evaluated the HSM surface with gradient surface metrics (GSM) and with two resistance-based models (RBM) based on least cost path (LCP) and commute distance (CD), in addition to an isolation-by-distance (IBD) model based on Euclidean distance. We compared the ability of these competing models of connectivity to explain pairwise genetic distances (RST) previously calculated from ten microsatellite genotypes of 454 beetles collected from 17 sites across Indiana, United States. Model selection with maximum likelihood population effects (MLPE) models found that GSM were most effective at explaining pairwise genetic distances as a proxy for gene flow across the landscape, followed by the landscape metrics calculated from the PMM, whereas the LCP model performed worse than both the CD and the isolation by distance model. We argue that the analysis of a continuous HSM with GSM might perform better because of their combined ability to effectively represent and quantify the continuous degree of landscape complementation (i.e., availability of complementary habitats in vicinity) found at and in-between sites, on which these beetles depend. Our findings may inform future studies that seek to model habitat connectivity in complex heterogeneous landscapes as natural habitats continue to become more fragmented in the Anthropocene.Open-Access-Publikationsfonds 202
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
The Ecological Consequences of Hummingbird Pollination for Plant Mating Systems
Get PDFPlant-pollinator interactions are an essential component of the ecology and evolution of natural and agricultural ecosystems, as they drive the ecological process of pollination and determine the outcomes of plant mating. My PhD thesis capitalized on plant-pollinator interactions in Heliconia tortuosa Griggs (Heliconiaceae) to understand the role of the ecological process of pollination as a driver of the outcomes of plant mating. The ecological process of pollination in H. tortuosa is exclusively mediated by territorial and trapline foraging hummingbirds. My PhD thesis combined a landscape-scale observational field survey, a variety of techniques of molecular biology, and a breadth of methods in statistical analysis to evaluate the interplay of ecology and evolution through the process of pollination. In Chapter 2, I found that patterns of pollen-mediated gene flow in H. tortuosa are characterized by a signature that is consistent with the behaviour of trapline foraging pollinators. I demonstrated that patterns of pollen-mediated gene flow can provide information to infer the foraging behaviour of pollinators. In Chapter 3, I found that deforestation altered the composition of the pollinator community through the decline of trapline foraging pollinators. This impact reduced the quality of pollen received by H. tortuosa individuals, as it reduced the genetic diversity of progeny and enhanced inbreeding. Given this perspective, I identified important implications for the conservation of plant-pollinator interactions. In Chapter 4, I found novel consequences of the foraging behaviour of pollinators for patterns of cross-fertilization and multiple paternity in H. tortuosa, with particular attention to the impact of trapline foraging. I demonstrated that variation in the foraging behaviour of pollinators can have divergent implications for the outcomes of plant mating. My PhD thesis demonstrated that disparities in the pollen transport mechanism can have profound implications for the ecology and evolution of plant mating. In particular, my PhD thesis revealed that the foraging behaviour of pollinators and the composition of the pollinator community are fundamental factors that determine patterns of pollen-mediated gene flow, self-fertilization, cross-fertilization, and multiple paternity in plants. Collectively, my PhD thesis contributed to a rich literature that has established a dialogue of ecology and evolution in the study of plant-pollinator interactions.Ph.D.2023-05-11 00:00:0
Conserving Connectivity: Ecological Determinants of Gene Flow in Plants at the Landscape Scale
No full textWith intensifying global pressures of habitat loss and fragmentation, there is an increasing need to manage landscapes in a way that maintains gene flow among previously continuous populations. This requires a detailed understanding of the scale of gene flow in nature and of how aspects of the landscape support or inhibit movement. In plants, gene flow occurs through both pollen and seed, each of which may be carried by multiple vectors. This makes it challenging to characterize, and as a consequence, our understanding of the local and landscape drivers of gene flow are limited in plants compared to animals. My thesis addresses this deficiency by quantifying the contributions of landscape structure, individual plant characteristics, and directed seed dispersal to gene flow of plants in fragmented landscapes. First, I used simulations to test if models of pollen flow could be improved by incorporating individual plant characteristics that affect attractiveness to pollinators. The results showed that inter-individual variation in attractiveness explained significantly more variation than inter-mate distance. Second, I took advantage of a network of calcareous grasslands in Germany to quantify the determinants of pollen and seed-mediated gene flow in a specialist herb, Pulsatilla vulgaris. Using 1,449 individuals from 57 populations, genotyped at seven newly developed markers, I tested the efficacy of an ecological shepherding network to maintain seed-mediated gene flow among P. vulgaris populations. I found that (i) shepherding distance explained genetic differentiation better than geographic distance among populations, (ii) populations that were well connected within the network had significantly higher genetic diversity, and (iii) genetic diversity was significantly positively correlated with fitness-related traits. Paternity analysis on a subset of seven populations revealed high rates of self-pollination. Within-population patterns of pollen flow correlated with floral resources measured at the scale of individuals and patches, whereas among-population pollen flow correlated with floral resources measured at the patch scale and landscape context measured at intermediate and large spatial scales. Together my results highlight the importance of using multi-scale and multi-vector approaches when modeling gene flow in plants, and suggests that typical models based on distance alone may be insufficient to capture the complexity of pollination and seed dispersal.Ph.D
Effects of Rotational Shepherding on Plant Dispersal and Gene Flow in Fragmented Calcareous Grasslands
No full textUnderstanding dispersal and gene flow in human-modified landscapes is crucial for effective conservation. Seed dispersal governs colonization, recruitment, and distribution of plant species, whereas both pollen and seed dispersal determine gene flow among populations. This PhD thesis tests the effect of rotational shepherding on seed dispersal and gene flow in fragmented calcareous grasslands. Calcareous grasslands (Gentiano-Koelerietum pyramidatae vegetation) in Central Europe are semi-natural communities traditionally used for rotational grazing that experienced a decline of plant species during the 20th century due to abandonment of shepherding. This PhD profits from a management project started in 1989 in Bavaria, Germany to reconnect previously abandoned calcareous grasslands in three non-overlapping shepherding systems. Two vegetation surveys in 1989 and 2009 revealed colonizations in previously abandoned grasslands reconnected by shepherding. First, I propose a comprehensive approach to identify determinants of community-level patch colonization rates based on 48 habitat specialist plants by testing competing models of pre-dispersal and dispersal effects and accounting for post-dispersal effects. Mean source patch species occupancy in 1989, and structural elements in focal patches related to establishment explained community-level patch colonization rates. Secondly, by adapting the community analysis to all 31 individual species of the same community with sufficient data, I corroborate the role of shepherding to support dispersal for a range of species, even if they lack seed morphological traits related to zoochory. Thirdly, for the habitat specialist Dianthus carthusianorum, I genotyped 1,613 individuals from 64 populations at eleven microsatellites to test the effect of dispersal by sheep on spatial genetic structure at the landscape scale. Genetic distances between grazed patches of the same herding system were related to distance along herding routes, whereas ungrazed patches showed isolation by geographic distance. Lastly, within individual grassland patches, shepherding significantly decreases the degree of relatedness among neighboring individuals (kinship structure) and increases genetic diversity. My thesis contributes towards understanding the effects of zoochory on spatial dynamics in plant populations across scales.Ph
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