1,721,060 research outputs found
On the morphological, biological and genetic heterogeneity of the genus Orchis (Orchidaceae, Orchidinae)
No full textTyteca, Daniel, Ceinos, Manon, Gathoye, Jean-Louis, Brys, Rein, Jacquemyn, Hans (2012): On the morphological, biological and genetic heterogeneity of the genus Orchis (Orchidaceae, Orchidinae). Phytotaxa 75 (1): 19-32, DOI: 10.11646/phytotaxa.75.1.2, URL: http://biotaxa.org/Phytotaxa/article/view/22
Far-reaching effects of root herbivory on pollinator-interactions and plant performance in Cynoglossum officinale
Get PDFBestuivers en bestuiving in stedelijke gebieden
No full textThe immense increase in human population numbers over the 20th century has had pronounced consequences on virtually all ecosystems. Firstly, vast amounts of land were taken intocultivation to feed the rising population. Secondly, all these new peopleneeded houses to live in which also led to large amounts of land being adaptedto meet the housing needs of humans. Both forms of land use significantlyaltered and for the most part destroyed native ecosystems and replaced themwith new and mostly degraded ones.Research on the effects of these land uses on ecosystems and ecosystem functions has long been focused primarily on agricultural land use as the dramatic impacts of new chemicals and pesticidesthat were widely used in modern agriculture became apparent soon after theyfirst started being used. The other major form of anthropogenic land use urban land use has long been relatively neglected by ecological scientists.Yet, this land use also takes up large amounts of land all over the globe andhas in the last decades been shown to have drastic impacts (both similar anddistinct from the ones originating from agricultural land use) on ecosystemsand ecosystem processes. Moreover, urbanization is ever increasing andknowledge on its impacts on ecosystems is crucial for sustaining ecosystemfunctioning in existing urban areas and for sustainable planning in newlyurbanizing regions.One very important ecosystem process is pollination. Most plant species rely on pollinators for successful reproduction and the pollinators in turn rely on the plants to provide them with resourcesto feed themselves and their offspring. As this interaction between organismgroups is of vital importance to sustaining ecosystem functioning, it isimportant to gain insights into how both organism groups are affected by urbanland use. An obvious aspect of urban land use is the extreme fragmentation thatit causes leaving behind small, remnant patches of (native?) vegetation thatare strongly isolated in space by an inhospitable matrix. For plants, thismeans that the gene flow through transport of pollen is likely to get moredifficult and for pollinators this means that they will have to travel furtherto obtain the resources they need.In this research we looked into the effects of urban land use on both organism groups in gradients of urban to rural land use. These gradients were laid out mainly around Leuven (but also Ghent,Hasselt, and Mechelen) and ranged from the inner city core over the cityoutskirts to the rural countryside around the city. We also looked further intothe nature of the rural countryside as different types of rural can exertdifferent influences on pollinator communities and consequently on plantpollination. This, of course, is an abstraction as the reality of landscapes isa continuum in which various land uses occur alongside each other in varyingamounts. The position of urban areas in terms of pollinator communities within theurban-rural continuum remains unclear. We studied pollinator communities of thetwo main pollinating insect groups in our region bees (Apidae) and hoverflies(Syrphidae) along two river systems which cross a gradient of urban toagricultural rural to semi-natural rural areas. We grouped the sites into threesite types (urban, rural-agricultural, and rural-natural) based on thesurrounding land use. We compared pollinator communities between these threesite types in general terms of abundance, alpha and beta diversity, but alsoassessed differences in species composition. Both abundance and diversity ofthe two pollinator groups was reduced in agricultural and urban sites comparedto the more (semi-)natural sites. Wealso observed that hoverflies and bees respond differently to different landuses. These differences stress the importance of incorporating all types ofland use practice to get a clear view on how urban land use may affect aspecific pollinator group.Urban areas consist mainly of a matrix that is inhospitable to bees but they also contain large public green spaces that are a potential habitat for bees if managed properly and therefore provide agood opportunity for bee conservation. Since urban green spaces are usually notdesigned to optimize resources for bees, we studied public green spaces in an urban-peri-urbangradient to detect which variables (local and/or regional) drive differences inabundance, diversity, and species composition of bee communities. Our resultsindicated that overall abundance is mainly driven by the cover of Fabaceae inpublic green spaces; these are largely made up of lawns in which Trifolium repens is the mainrepresentative of the Fabaceae. Increasingly urban land use decreased beediversity and also altered the species composition of the communities. However,the negative effects of urban land use were counteracted by the management ofthe public green space with (partly) extensively managed sites scoring overallbetter for bee abundance and diversity than the traditional, highly manicuredsites. We concluded that adapting the management of public green spaces toallow for diverse plant communities that ensure continuous flowering couldgreatly improve the urban bee communities and could lead to public green spacesin urban areas becoming favorable bee habitats.Changes in pollinator faunas due to urban land use are expected to also cause changes in both plant-pollinator interactions and increased pollen limitation in plants (seed set limited by amount of pollendeposited and therefore suboptimal). We therefore investigated the effects of urban land useon pollinator diversity, flower visitation rates to and reproductive success of Digitalis purpurea (self-incompatible) in experimental populations in three urban-rural gradients and contrasted theseagainst two large, natural populations. In the experimental populations wequantified the visitation rates of pollinators to the flowers and appliedsupplemental hand-pollinations to determine the level of pollen limitation onseed set. We found no impact of urban land use on pollinator diversity at any of the locationsand also the visitation rates did not differ significantly between urban andrural populations. Reproductive success appeared, however, pollen limited inall sites, even in the large and optimal reference populations. This led us toconclude that the pollen limitation was caused by a bet-hedging strategy of thespecies rather than by insufficient pollination. This species is monocarpic and only flowers for one season.Therefore on days with high pollinator visitation rates this bet-hedgingstrategy allows the plant to compensate for days with low pollinator visitationrates.We then studied bee abundance, flowervisitation rates to, and seed set of Trifoliumrepens in public lawns in an urban-peri-urban gradient around Leuven,Belgium, to check in how far these experimental results applied to real-worldplant population. T. repens (white clover) is an obligately outcrossing plant and seed set is therefore sensitive to pollen limitation. We explored relationships between visitation rates andseed set on the one hand with both lawn and matrix variables on the other hand.The two variables that best explained visitation rates to flowers were theabundance of the plant species in the lawns and the amount of green areas(gardens, parks, grasslands) in the surroundings. Surprisingly, an increasingamount of green areas in the surroundings had a negative effect on both flowervisitation rates to, and seed set of T. repens. Bumblebees (the main pollinators) responded positively to urban land use resulting in more flower visits by this group and an increased seed set inthe more urban sites. This was probably caused by a concentration effect of thepollinators in our study sites in the city center as these were the major foodsources for them due to lack of alternatives. Responses will likely differ forother bee and plant species, but this shows that at least for this species,pollination is not compromised by urbanization. <w:latentstyles deflockedstate="false" defunhidewhenused="true" <w:lsdexception="" locked="false" priority="0" semihidden="false" status: Publishe
Alternative methods for assessing habitat quality in freshwater systems
Get PDF“Water, water, everywhere…”. 71% of the earth’s surface is covered by water, freshwater representing 2.5% of it, and only 1% being accessible. Due, largely to a number of anthropogenic activities (pollution, habitats modification) coupled with the impacts of climate change, a dramatic decline in biodiversity is occurring across all earth’s ecosystems. Surprisingly, freshwater ecosystems receive considerably less attention than many other habitats and therefore, effective biodiversity monitoring programs are urgently needed to assess the health and state of the endangered and threatened species in these aquatic systems. Further, current techniques utilised to survey freshwater ecosystems are often considered ineffective, invasive, time consuming and biased. As a result, the implementation of molecular-based detection tools are attractive options as they are often shown to be more sensitive and cost effective. The use of environmental DNA (eDNA) detection is one such molecular tool which is showing promising results, due to its high reliability, sensitivity and non-invasiveness characters. However, recent studies have highlighted potential limitations associated with eDNA-based detection. Such limitations may lead to a decrease in the confidence of this method. The aim of this thesis was to investigate the use of eDNA-based detection across a number of species and a number of systems, all as a proxy of habitat quality. Stringent laboratory practices and validation guidelines were adhered to, allowing for reliable quality assessments of newly designed eDNA assays outlined in this thesis. Moreover, distinct controlled mesocosm experiments allowed the investigation of critical factors, part of the sampling method or analysis processes leading to an optimisation of eDNA collection and decreasing the rates of false negative results. Several comparison between traditional monitoring techniques and the novel assays were also performed aiding in the confidence of these new methods. Interestingly, the results obtained in this thesis shows a similar efficiency between traditional and eDNA-based methods for monitoring invasive species, but a higher efficiency of eDNA detection when detecting rare or low abundant organisms (i.e. those that are endangered or threatened). Furthermore, this thesis reports an extreme example where a species was found at a number of locations within a stretch of a river, yet undetected with the eDNA assay. In this chapter eDNA detection was only possible when I utilised ddPCR rather than qPCR (the more standard technique for assessing eDNA in any given system). Overall, eDNA detection was found to be an effective tool for assessing the presence of invasive and/or endangered species, increasing theknowledge on their distribution and the impact of future management plans. In this thesis, chapters 2, 3, 4, 5 and 6 are organised as case studies, aiming to highlight benefits and limitations of species-specific detection using eDNA
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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