1,721,109 research outputs found
Lack of pre-dispersal seed predators in introduced Asteraceae in New Zealand
No full textThe idea that naturalised invading plants have fewer phytophagous insects associated with them in their new environment relative to their native range is often assumed, but quantitative data are few and mostly refer to pests on crop species. In this study, the incidence of seed-eating insect larvae in flowerheads of naturalised Asteraceae in New Zealand is compared with that in Britain where the species are native. Similar surveys were carried out in both countries by sampling 200 flowerheads of three populations of the same thirteen species. In the New Zealand populations only one seed-eating insect larva was found in 7800 flowerheads (0.013% infected flowerheads, all species combined) in contrast with the British populations which had 487 (6.24%) flowerheads infested. Possible reasons for the low colonization level of the introduced Asteraceae by native insects in New Zealand are 1) the relatively recent introduction of the plants (100-200 years), 2) their phylogenetic distance from the native flora, and 3) the specialised nature of the bud-infesting habit of the insects
Quantifying individual feeding variability: implications for mollusc feeding experiments
No full text1. In order to quantify the level of variability in seedling consumption displayed by individual molluscs, we placed one snail (Helix aspersa) in each of 51 trays containing (7-day-old) Taraxacum officinale seedlings for 7 days.
2. Initially, individual snails displayed considerable variability in their consumption of seedlings; however, this variability declined with time. The consumption of seedlings was not related to individual snail mass.
3. A second grazing experiment, using five different snail densities in similar experimental conditions to the first, showed that increasing snail number reduced variability within treatment groups.
4. A computer simulation, based on data from the first experiment correctly predicted the basic form of the decline in feeding variability with increasing snail density found in the second. Post hoc changes to the model, based on empirical analysis of the second experiment to account for mutual interference, reduced discrepancies between empirical and model results.
5. This study highlights the consequences that individual feeding behaviour has on feeding trials with molluscs, and provides a simple method by which this variability can be quantified and accommodated within experimental design
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Relationship between capitulum size and pre-dispersal seed predation by insect larvae in common Asteraceae
No full textThe evolution of a showy floral display as an advertisement to pollinators could simultaneously advertise the availability of resources to pre-dispersal seed-predators. The hypotheses tested here are that the incidence of seed predation by bud-infesting insect larvae in capitula of Asteraceae is positively related to (1) capitulum size among species, (2) capitulum size within species, (3) capitulum lifespan, and (4) the degree of flowering asynchrony on individual plants. Three populations of each of 20 common herbaceous species of Asteraceae from disturbed ground and grassland habitats were monitored for the presence of pre-dispersal, seed-eating insect larvae. Mean capitulum size (receptacle width) of each species was measured. In a sub-set of eight species, individual capitula were tagged to determine their flowering phenology and lifespan (from anthesis to seed shedding). From these data an index of flowering synchrony on individual plants was derived. Among species, the incidence of larval infestation increased with capitulum size. Small-flowered species such as Achillea millefolium were largely free of bud-infesting larvae, whilst large-flowered species such as Arctium minus were heavily infested. In three cases investigated in greater detail, bud infestation was found to increase with capitulum size within species, suggesting a potential for natural selection to favour smaller capitula. No relationship was found between infestation levels and either capitulum lifespan or degree of flowering synchrony, and there was no evidence that the relationship between capitulum size and infestation was confounded by correlations with these other features. The results support hypotheses I and 2, but not 3 and 4. It is suggested that the characteristic capitulum size of each species may represent a trade-off between the opposing selection pressures of pollinators and pre-dispersal seed predators. <br/
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Reproductive features of Celmisia species (Asteraceae) in relation to altitude and geographical range in New Zealand
No full textA range of seed and flower characters was examined in 37 species of the New Zealand genus Celmisia (Asteraceae)
to determine whether there were any relationships between reproductive features and the geographic or altitudinal
ranges of the species. Using published sources and herbarium material, flower attractiveness to pollinators was
measured in terms of capitulum size and ray/disc length ratio. Dispersibility was measured in terms of seed dry
weight, seed terminal velocity, pappus/seed length ratio, and scapdeaf length ratio. Altitude (minimum and
maximum) and geographic ranges (number of 1" latitude x 1" longitude squares occupied) were obtained from
published sources. A multivariate principal components analysis using 12 morphological characters revealed the
presence of five groups of species differing in capitulum size, seed weight, pappus length, number of pappus bristles,
leaf length and scape length. Linear regressions showed that altitude was significantly and negatively related to
seed dry weight and capitulum size, and positively to scapdeaf length ratio. Geographic range is negatively related
to capitulum size, and positively to ray/disc ratio and altitudinal range. Amongst the seed features measured, seed
weight was the best predictor of terminal velocity (an inverse measure of dispersability), but lighter seeds also had
a higher pappudseed length ratio. The frequency distribution of the geographic ranges of the species is highly
skewed, with many local species (86% occurring in 15 or fewer one-degree squares) and very few common ones.
Two species (C. gracilenta and C. grarninifolia) are notably more common than all the others. A comparison of
these species with the others shows that, on average, they have lighter seeds with more bristles, taller scapes and
higher ray/disc ratios, but have smaller capitula. The low geographic abundance of the rare species could not readily
be attributed to any specific reproductive feature, possibly because of the multiple types of rarity represented within
the genus
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