1,720,964 research outputs found
Plant stress and the prevalence of pests and pathogens associated with a native and an invasive alien legume tree in the Cape Floristic Region, South Africa
Get PDFThesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Invasive alien plant species have devastating effects on the environments that they invade. Australian Acacias, a group of plants that has been planted globally for a range of uses, but has escape plantation areas and became invasive in many countries, are particularly problematic. Acacia mearnsii is one of these invasive alien plant species and in South Africa it is also an important forestry species. It is currently the fifth most widespread invasive alien plant in South Africa, only restricted by the very arid Karoo, thus it is important to assess the different habitats that it enters. The Afromontane forest complex in South Africa is highly fragmented and is one of the most threatened Biomes in the country. The widespread forest margin tree Virgilia divaricata occurs within these forest margins. It is ecologically similar to A. mearnsii as these two species share many characteristics (nodulating legumes, forest pioneer species, fast growing and fire adapted). These species occur sympatrically within invaded forest margins and within these sites, there is a potential for biological exchanges of associated pests and pathogens in the form of arthropods and fungal species. We hypothesize that these two species have different interactions with their pests and pathogens in accordance with the Enemy Release Hypothesis (ERH) and the Biotic Resistance Hypothesis (BRH), respectively. We first compared arthropod associates between these two tree species and found that they share many arthropod species. The native tree did, however, have much higher abundances of herbivores and overall arthropod associates than the invasive tree species, which supports the predictions of the ERH. The distribution of these two species also had an effect on their arthropod assemblages. We assessed their ophiostomatoid fungal associates and herbivore loads and then determined how these pests and pathogens were influenced by environmental conditions along a water gradient. We also compared the effect of plant nutrient content of the two tree species on pest and pathogen loads. A. mearnsii was unaffected by water limitation along this gradient, while δ12C/ δ13C analyses showed that V. divaricata trees experienced drought within drier sites. V. divaricata also had higher herbivore loads in drier sites. A. mearnsii had higher herbivore loads on nutrient deficient trees and higher disease development in trees with sufficient nutrient levels. Comparisons of the nutrient economies of the two legume trees showed that they had similar leaf nutrient contents and resorption efficiencies, but they differed in the use of Biological Nitrogen Fixation (BNF). The native tree utilized BNF more than the invasive. We also tested the physiological effects of a native fungal species on the two tree species. We found the infection elicited more response from the invasive, while the native plant was almost non-responsive. Both plants had significantly longer lesions on infected seedlings than on control plants after inoculation with this pathogen. This difference in response offers a measure of support to the BRH, as the invasive may be more vulnerable to infection. The importance of using related, ecologically similar species in the assessment of the impacts of invasive alien plants is highlighted here. This may provide more information on the actual ecological interaction between native and invasive species within invaded ranges. Forest margins are very vulnerable and dynamic habitats. The influx of a new species into this habitat in the form of an invasive alien plant may therefore have much negative effects. We found support for the exchange of pest and pathogens where these two tree species co-occur. The two host species were very similar in their nutrient economies, creating a potential for competition for similar resources between A. mearnsii and V. divaricata. The environment had an influence on how these plants responded to pest and pathogens and this may be important under the predicted scenario of future climate change.AFRIKAANSE OPSOMMING: Uitheemse indringer plant spesies het vernietigende effekte op die omgewings waarbinne hulle indring. Australiese Acacias, ‗n groep plante wat reg oor die wêreld aangeplant is vir ‗n reeks gebruike, maar wat uit plantasie areas ontsnap het en indringers geword het in baie lande, is besonder problematies. Acacia mearnsii is een van hierdie indringer uitheemse plant spesies, en in Suid Afrika is ook ‗n belangrike bosbou spesie. Dit is tans die vyfde mees wydverspreide uitheemse indringer plant in Suid Afrika, en word slegs beperk deur die baie droë Karoo, so dit is belangrik om die verskillende habitatte wat dit binnedring te ondersoek. Woudrandte, the grense van die Afromontane woudkompleks in Suid Afrika, is hoogs gefragmenteerd en is dus een van die mees bedreigde Biome in die land. Die wydverspreide woudrand boom Virgilia divaricata kom in hierdie woudrandte voor. Dit is ekologies eenders aan A. mearnsii, aangesien hierdie twee spesies baie kenmerke deel (wortelknop-vormende peulplante, woudpionier spesies, vining groeiend, aangepas tot brande). Hierdie spesies kom simpatries voor binne woudrandte wat deur A. mearnsii ingedring is, en in hierdie lokaliteite bestaan daar die potensiaal vir biologiese uitruiling van geassosieerde peste en patogene in die vorm van geleedpotiges en fungi spesies. Ons stel die hipotese dat hierdie twee spesies verkillende interaksies met hulle peste en patogene het, in ooreenstemming met die Vyand-Vrystellingshipotese (VVH) en die Biologiese-Weerstandshipotese (BWH), onderskeidelik. Ons het eers die geleedpotige assosieasie tussen hierdie twee boom spesies vergelyk en het bevind dat hulle baie geleedpotige spesies deel. Die inheemse boom het egter baie hoër getalle herbivore en algehele geleedpotige-assosiasies gehad as die indringer boom spesie, wat die voorspellings van die VVH ondersteun. Die verspreiding van hierdie twee spesies het ook ‗n effek gehad op hulle geleedpotige samestellings. Ons het ook hulle geassosieerde ophiostomatiede fungus assosiate en hulle herbivoor ladings bestudeer, en het bepaal hoe hierdie peste en patogene deur omgewingstoestande beinvloed is langs ‗n water gradient. Ons het ook die effek van hierdie peste en patogene op die voedingstof-inhoud van hierdie twee spesies vergelyk. A. meansii is nie geaffekteer deur waterbeperkings langs hierdie gradient nie, terwyl δ12C/ δ13C analises aangedui het dat V. divaricata bome droogte stres in droër lokaliteite ervaar het. V. divaricata het ook hoër herbivoorladings gehad in die droër lokaliteite. A. meanrsii het hoër herbivoorladings gehad op voedingstof-beperkte bome, en daar was verhoogde siekte-ontwikkeling in bome met genoegsame voiding. Vergelykings van die voedingstof-ekonomië van die twee peulplant bome het aangedui dat hulle eenderse blaarvoedingstof-inhoude en resorpsie effektiwiteite het, maar het verskil in die gebruik van Biologiese Stikstof Fiksasie (BSF). Die inheemse boom het meer van BSF gebruik gemaak as die indringer. Ons het ook die fisiologiese effekte van ‗n inheemse fungus spesie op die twee boomspesies getoets. Ons het bevind dat infeksie ‗n sterker reaksie in die indringer ontlok het, terwyl die inheemse plant feitlik glad nie op infeksie gereageer het nie. Beide plante het beduidend langer wondmerke in geinfekteerde saailinge ontwikkel as in kontrole plante na innokulasie met die patogeen. Hierdie verskil in reaksie verleen ‗n mate van ondersteuning aan die BWH, aangesien die indringer meer vatbaar mag wees teen infeksie. Die belang daarvan om verwante, ekologies soortgelyke spesies te gebruik in die bepaling van die effekte van uitheemse indringer spesies word hier beklemtoon. Dit mag meer inligting verskaf oor die werklike ekologiese interaksie tussen inheemse en indringer spesies binne verspreidings wat binnegedring is. Woudrandte is baie weerlose en dinamiese habitatte. Die invoer van nuwe spesies in hierdie habitat in die vorm van ‗n uitheemse indringer plant mag daarom baie negatiewe effekte hê. Ons het ondersteuning gevind vir die uitruiling van peste en patogene waar hierdie twee spesies saam voorkom. Hierdie spesies was baie eenders in terme van hulle voedingstof-ekonomië, wat die potensiaal skep vir kompetisie tussen A. mearnsii en V. divaricata. Die omgewing het ‗n effek gehad op hoe hierdie plante gereageer het op peste en patogene, en dit mag belangrik wees onder die huidig voorspelde senarios van toekomstige klimaatsverandering
Comparing the IUCN’s EICAT and Red List to improve assessments of the impact of biological invasions
Get PDFCITATION: Van der Colff, D. et al. 2020. Comparing the IUCN’s EICAT and Red List to improve assessments of the impact of biological invasions. NeoBiota 62, 509-523.The IUCN recommends the use of two distinct schemes to assess the impacts of biological invasions on biodiversity at the species level. The IUCN Red List of Threatened Species (Red List) categorises native species based on their risk of extinction. Such assessments evaluate the extent to which different pressures, including alien species, threaten native species. The much newer IUCN Environmental Impact Classification for Alien Taxa (EICAT) categorises alien species on the degree to which they have impacted native species. Conceptually, the schemes are related. One would expect that: 1) if a native species is assessed as threatened under the Red List due to the impacts of alien species, then at least one alien species involved should be classified as harmful under EICAT; and 2) if an alien species is assessed as harmful under EICAT, then at least one native species impacted should be assessed as threatened by alien species under the Red List. Here we test this by comparing the impacts of alien gastropods, assessed using EICAT, to the impact on native species as assessed based on the Red List. We found a weak positive correlation, but it is clear there is not a simple one-to-one relationship. We hypothesise that the relationship between EICAT and the Red List statuses will follow one of three forms: i) the EICAT status of an alien species is closely correlated to the Red List status of the impacted native species; ii) the alien species is classed as ‘harmful’ under EICAT, but it does not threaten the native species with extinction as per the Red List (for example, the impacted native species is still widespread or abundant despite significant negative impacts from the alien species); or iii) the native species is classified as threatened under the Red List regardless of the impacts of the alien species (threatened species are impacted by other pressures with alien species potentially a passenger and not a driver of change). We conclude that the two schemes are complementary rather than equivalent, and provide some recommendations for how categorisations and data can be used in concert
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
