1,721,046 research outputs found
Ecological implications of introducing Leucaspius delineatus (Heckel, 1843) and Pseudorasbora parva (Temminck and Schlegel, 1842) into inland waters in England
Get PDFNon-native species invasions threaten the structure, function and biodiversity of ecosystems worldwide, and those of non-native fishes pose amongst the greatest threats to inland waters of the U.K. This PhD investigated the establishment, dispersal and ecological implications of introducing the two non-native fish species, sunbleak Leucaspius delineatus (Heckel, 1843) and topmouth gudgeon Pseudorasbora parva (Temminck and Schlegel, 1842) to inland waters of England. The introduction and initial dispersal of both species can be attributed to the commercial fish trade. Species-specific variability of life history, growth and morphological traits was examined in sunbleak (12 sites) and topmouth gudgeon (3 sites) to assess their role in establishment success. The drift dynamics, i.e. timing and intensity (propagule pressure), of sunbleak and topmouth gudgeon were assessed for source populations to determine dispersal potential. Potential risks for native species posed by these two alien cyprinids were assessed with respect to the parasite fauna and overlaps in resource use. For sunbleak, these were also examined in terms of social integration of this species into a native fish assemblage. Biological resistance to topmouth gudgeon invasion was evaluated by stomach flushing and gut content analysis of native piscivorous fishes.Inter-population variability in life histories and morphological characters were observed in both sunbleak and topmouth gudgeon. Populations of both species matured at small body sizes and between the ages 1 and 2. The fish were of good body condition and exhibited high reproductive investment. In both species, dispersal from source waters followed a diel pattern, with higher rates at night than during the day (e.g. maximum drift densities during May of 2004 and 2005: 9-10 sunbleak per 1000 m -3 at about 23:00 hrs; 40-52 topmouth gudgeon per 1000 m -3 at about 05:00 hrs). Downstream of one source population, microhabitat use of topmouth gudgeon was found to overlap with native species (brown trout Salmo trutta L., European chub Leuciscus cephalus (L.), bullhead Cottus gobio L., stoneloach Barbatula barbatula (L.); both brown trout and chub were observed to prey on topmouth gudgeon. However, predation intensity may be density-dependent and of insufficient level to impede topmouth gudgeon establishment, which was facilitated in the receiving stream by the consistent propagule pressure from on-line source populations. Sunbleak diet and microhabitat use also overlapped with native species (roach Rutilus rutilus (L.) and common bream Abramis brama (L.)) as young larvae, but this decreased with age. Social network analysis of sunbleak-native species interactions revealed that sunbleak creates significantly stronger social bonds with the native species than do natives amongst themselves.No macro-parasites were found in topmouth gudgeon, but two ‘Category II’ non-native parasites Neoergasilus japonicus (Harada, 1930) and Ergasilus briani (Markewitsch, 1932) were found in some populations of sunbleak. The potential for sunbleak to spread beyond their current distribution in England and the species’ social integration behaviour may facilitate the dispersal of these parasites, which may spread faster among communities invaded by sunbleak than in those where this non-native species is absent. The results of this PhD study are discussed within their wider context and their relevance to non-native species risk analysis and management
Do non-native fish as prey favour the conservation of the threatened indigenous Eurasian otter?
Get PDF1. Biological invasions are considered a major threat to biodiversity. Most research has focused on the distribution, biology and impacts of non-native species on native fauna and flora. However, few studies have explored their role as prey for native predators of conservation concern. 2. To assess the incidence and intensity of predation by the Eurasian otter Lutra lutra on established non-native fish species, data were collated from the published literature. To be selected, studies had to cover at least 1 year, analyse more than 100 spraints and report the study period and percentage relative frequency (%RF) of all prey fish species. 3. To permit reliable, time-related comparisons with %RF of non-native fishes in otter diet, we also reviewed available information about both the distribution of non-native fishes and history of their introductions to European countries, revealing a decrease with longitude in the number of naturalised non-native fishes taken (ranging between 5 and 34) and their percentage in each fish assemblage. 4. Our selective criteria were met by 30 dietary studies from 44 study areas in 15 European countries during 1970-2010. The extent to which otters rely on non-native fishes was almost negligible (mean %RF = 4.8), with the number of non-native fishes preyed upon by otters decreasing with both latitude and longitude. 5. The %RF of non-native fish in the diet increased slightly with time, with otters preying significantly more on non-native fish in study areas where alterations of the fish assemblage had been highlighted in the reference papers. No relationship was found between otter diet breadth and the occurrence of non-native fishes in their diet. 6. The current role of non-native species in otter diet suggests that effective otter conservation management plans should focus on the maintenance and⁄or enhancement of native fish assemblages
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
Genetic and genomic approaches to the conservation of the threatened crucian carp Carassius carassius (L.) : phylogeography, hybridisation and introgression
Get PDFBiological invasions can have dramatic detrimental impacts on ecosystems, however they also represent rich opportunities to study the evolutionary processes associated with them. Hybridisation and subsequent introgression are two such processes and are common among native and non-native species. The crucian carp, Carassius carassius (L.), is a European freshwater fish that is threatened throughout much of its native range by several factors including hybridisation and introgression with three non-native species, the goldfish, Carassius auratus (L.), the gibel carp, Carassius gibelio (Bloch), and the common carp, Cyprinus carpio (L.). The conservation of C. carassius is hampered by a lack of phylogeographic knowledge for the species and no knowledge of the extent or impact of hybridisation and introgression. Contemporary genomic approaches such as Restriction Site Associated DNA sequencing (RADseq) can offer unprecedented insights into such research areas, however RADseq comes with several sources of potential bias. Exploratory analyses in Chapter 2 show that two sources of bias in particular, null alleles and over merged ohnolog loci, are highly important in this dataset, but can be filtered using population genetics statistics. The filtered dataset is used in phylogeographic analyses in Chapter 3, along with microsatellite and mitochondrial DNA and show that C. carassius exists as two major lineages in Europe, which diverged approximately 2.26 million years ago, and should be treated as separate units for conservation. These lineages result from the C. carassius postglacial recolonisation routes thtough Europe, which are highly distinct from the general patterns seen in other freshwater fish species. These phylogeographic results showed high similarity between C. carassius in England and those in continental Europe, calling into question the presently assumed native status of C. carassius in England, which has been contentious in the past. Empirical tests of this status using microsatellites showed that, in fact, C. carassius is most likely introduced in England around the 15th century, raising interesting discussions pertaining to their conservation in the England. Lastly, in Chapter 5, microsatellite and RADseq approaches show that hybridisation between C. carassius and non-native species is prevalent where they are sympatric, however backcrosses are rare, and there is no evidence of further introgression between the species studied. Taken together, these results suggest that postzygotic mechanisms of isolation limit interspecific gene flow, and conservationists should focus further research on the direct impacts of non-native species and F1 hybrids
Genetic and genomic approaches to the conservation of the threatened crucian carp Carassius carassius (L.) : phylogeography, hybridisation and introgression
Get PDFBiological invasions can have dramatic detrimental impacts on ecosystems, however they also represent rich opportunities to study the evolutionary processes associated with them. Hybridisation and subsequent introgression are two such processes and are common among native and non-native species. The crucian carp, Carassius carassius (L.), is a European freshwater fish that is threatened throughout much of its native range by several factors including hybridisation and introgression with three non-native species, the goldfish, Carassius auratus (L.), the gibel carp, Carassius gibelio (Bloch), and the common carp, Cyprinus carpio (L.). The conservation of C. carassius is hampered by a lack of phylogeographic knowledge for the species and no knowledge of the extent or impact of hybridisation and introgression. Contemporary genomic approaches such as Restriction Site Associated DNA sequencing (RADseq) can offer unprecedented insights into such research areas, however RADseq comes with several sources of potential bias. Exploratory analyses in Chapter 2 show that two sources of bias in particular, null alleles and over merged ohnolog loci, are highly important in this dataset, but can be filtered using population genetics statistics. The filtered dataset is used in phylogeographic analyses in Chapter 3, along with microsatellite and mitochondrial DNA and show that C. carassius exists as two major lineages in Europe, which diverged approximately 2.26 million years ago, and should be treated as separate units for conservation. These lineages result from the C. carassius postglacial recolonisation routes thtough Europe, which are highly distinct from the general patterns seen in other freshwater fish species. These phylogeographic results showed high similarity between C. carassius in England and those in continental Europe, calling into question the presently assumed native status of C. carassius in England, which has been contentious in the past. Empirical tests of this status using microsatellites showed that, in fact, C. carassius is most likely introduced in England around the 15th century, raising interesting discussions pertaining to their conservation in the England. Lastly, in Chapter 5, microsatellite and RADseq approaches show that hybridisation between C. carassius and non-native species is prevalent where they are sympatric, however backcrosses are rare, and there is no evidence of further introgression between the species studied. Taken together, these results suggest that postzygotic mechanisms of isolation limit interspecific gene flow, and conservationists should focus further research on the direct impacts of non-native species and F1 hybrids
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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