1,721,017 research outputs found
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
Life history variation and diet preference in non-diadromous Otago galaxiids
Full text linkLife history theory states that selection acts upon individuals to produce optimal reproductive success, through maximising number of recruited offspring. Selection pressures vary across different environments and subsequently produce a wide variation in optimal life history, resulting in variation of life history traits. Previous research has identified that life history variation can occur across large scale latitudinal and elevational gradients and between small scale allopatric populations. Research concerning the diets and life history variation at early life stages, particularly in fish, is severely limited. This thesis investigates the importance of diets and resource availability on the observed life history variation between four species of the ‘Galaxias vulgaris complex’; G. anomalus, G. eldoni, G. depressiceps and G. pullus across an altitude gradient and between life history categories at the larval life stage.
Diet analyses displayed that Chironomidae were the most prevalent food item, which accounted for 62% of the observed diet contents, followed by Copepoda (20%) and Algae (8%). Chironomidae commonly dominate small freshwater fish diets, and as predicted, larval galaxiid populations displayed a correlation between larval galaxiid length and prey item size, as expected in gape-size limited fish. Additionally, species was observed to be a much poorer predictor of prey item length than either larval length or site. Galaxiids also displayed higher selectivity when exposed to extreme resource abundance. However, there were no significant trends observed between galaxiid diets and elevation or life history categories. Conversely, invertebrate communities displayed significantly greater diversity at fast life history populations than intermediate life history populations. Additionally, diets consistently displayed significantly lower diversity than their respective invertebrate community.
This research highlights the importance of investigating multiple selection pressures when attempting to discern causal effects of life history variation. It is likely that, while resource abundance is important in defining life history, other selection pressures, such as disturbance and predation may be acting as stronger selection pressures upon populations of larval galaxiids
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
Links between personality and individual niche in the freshwater fish Gobiomorphus cotidianus
No full textAll individuals within a population are unique. Individual variation in behaviour – or animal personality – occurs consistently throughout the animal kingdom. Understanding how individuals vary in their behaviour is imperative in fully deducing the impact that animal personalities can have at the population or even ecosystem level. Resource use has also been shown to consistently differ between individuals in a population, and can have effects on the strength and variety of interactions an animal has within its ecosystem. At present, there has been very little research on how the personality of an animal affects individual resource use, especially the comparison between behavioural variation and diet in a natural setting. The aim of this research was to investigate individual behavioural variation and resource use in a New Zealand freshwater fish (common bully, Gobiomorphus cotidianus), and understand how these individual parameters may affect both each other and an individual fish’s fitness. The individual behavioural variation of common bullies was examined through repeated assays of boldness, aggression and exploration in 93 fish. The habitat use, diet and growth of individuals were also repeatedly measured in pond mesocosms that mimicked the bullies’ natural ecosystem. Behavioural types, in particular individual boldness, were found to be moderately to strongly repeatable through time. There were also significant correlations between all behavioural types, where bolder fish were consistently more aggressive and more exploratory, establishing the existence of a proactive/reactive behavioural syndrome. 50% of the total dietary niche width of the population was accounted for by individual specialisation, while habitat use was found to be only weakly repeatable. It was found that behaviour was correlated with individual resource use in fish that had their personality analysed prior to their resource use, where more exploratory, less bold fish ate larger prey in shallower habitats. In contrast, correlations in fish that had their behaviour assayed after placement in mesocosms were non-significant. There were also no significant correlations between an individual’s growth, and its behaviour or resource use, though there was a near-significant tendency for more proactive fish to have slower growth rates. Overall, the discovery of this behavioural syndrome and resource specialisation is important as it highlights the uniqueness in how each individual reacts to different situations and how these could then feed through to alter predator-prey interactions. This could then affect abundances of species at trophic levels with which they are connected, and potentially the functioning and services an ecosystem provides. Ultimately, this study advances our understanding of the individualities of the behaviour and niche within this species, and gives insight into the possible mechanisms for effects that animal personalities can have on ecosystems
Effects of interspecific interactions on individual specialisation
Full text linkIn many species, some individuals are specialist users of a subset of the total resources available to their population, a phenomenon known as individual specialisation. This intraspecific variation has long been suspected of shaping population dynamics and has potentially large effects at the ecosystem level. Variation in the degree of individual specialisation can be driven by ecological interactions.
The common bully Gobiomorphus cotidianus, a New Zealand native fish, displays a generalised diet at the population level, with moderate levels of individual specialisation. Juvenile perch Perca fluviatilis compete for the same food resources, while larger perch are potential predators. These antagonistic biological interactions may have an impact on the trophic niche and the degree of individual specialisation in bullies.
I used surveys of fish communities and cross-sectional diet data to assess individual specialisation in wetland bully populations in relation to ecological factors. Then, in two series of controlled manipulative experiments, I asked how individual specialisation in bullies responded to intraspecific competition, interspecific competition and predation risk from perch. I hypothesised that ecological niches at the population and individual levels would vary according to the composition of the fish community. Finally, I led a collaborative comparative phylogenetic analysis of the literature which compiled indices of individual specialisation in diet across ecosystems and taxa and tested whether individual specialisation was predicted by cumulative measures of human impacts. I anticipated that due to global resource and habitat disruptions, human impacts on individual specialisation would generally be negative.
Consistent with the niche variation hypothesis, I found that intraspecific competition led to overall higher intraspecific diet diversity, while interspecific competition led to lower degrees of individual specialisation. Predation risk had a positive effect on dietary, and a negative effect on habitat individual specialisation. However, the direction of these effects changed when interspecific competition occurred along predation risk. At the population level, I recorded niche shifts due to interspecific competition both in habitat use and in diet.
Finally, I found negative effects of human activities on individual specialisation in terrestrial and freshwater ecosystems. There was however no evidence of a similar negative relationship in marine ecosystems. This discrepancy in results might be linked to differences in the types of drivers that impact individual specialisation between each ecosystem type.
This work underscores the importance of integrating individual variation when evaluating a population’s response to antagonistic biological interactions
The fight for coexistence: niche partitioning between kiore (Rattus exulans) and ship rats (Rattus rattus) on Chatham Island
No full textInvasive species are a major threat to biodiversity throughout the world. In New Zealand, invasive rats represent a significant threat to native species, especially to island seabird populations. In order to determine the ecological effects that rats have on their environment and on native species, we need information on their niche and interactions with other species. This information may then be used to inform management strategies to protect native species and control invasive rats. Furthermore, the presence and coexistence of different combinations of rodents on islands in New Zealand represents a major challenge for ecologists to explain. By investigating the mechanisms facilitating the coexistence of varying rodent combinations, we are able to improve our understanding of the interactions between rodents and how these interactions may affect other species around them.
The objective of my thesis was to identify the presence and level of interspecific competition between kiore (Rattus exulans) and ship rats (R. rattus) on Chatham Island to understand some of the mechanisms behind their coexistence and to determine the threat they pose to native species there. Specifically, I investigated the microhabitat structure and diet of kiore and ship rats in Tuku Nature Reserve on Chatham Island, New Zealand to determine whether niche partitioning may be occurring between these species. Multivariate analyses of floristic and microhabitat data using a canonical correspondence analysis and redundancy analysis, respectively, however, showed no evidence of microhabitat-niche partitioning between species. With the use of δ13C and δ15N, stable isotope analysis of kiore and ship rat tissues (liver, vibrissae and bone collagen) showed that segregation in isotopic space was occurring. I measured isotopic niche breadths using standard ellipse areas and their overlap between species for each tissue, vibrissae section and season, intraspecific isotopic variation within each species, the composition of prey sources using Bayesian mixing models, and seasonal isotopic variation between species and within species. Diet partitioning was indicated by the low isotopic niche overlap between species, by seasonal variation in the level of overlap between species, and in differences between kiore and ship rat niche breadths. However, Bayesian mixing models did not reveal major differences in diet composition between kiore and ship rats, with invertebrates, plants and the Chatham Island tāiko (Pterodroma magentae) being the most important food sources for both species. The occurrence of tāiko in the diet of both rats may either be due to direct predation or scavenging. Therefore, further studies are needed to determine whether these rats are directly impacting tāiko populations in order to prioritise eradications.
I concluded that diet partitioning was more important than microhabitat partitioning in explaining the coexistence of kiore and ship rats. However, it is possible that I was unable to detect microhabitat differences between kiore and ship rats by my methods so further studies should investigate not only sites that captured rats but those that did not to determine the microhabitat available, including sites that were not trap sites as this may have a sampling bias due to trap sites being chosen based on similar characteristics. Further mechanisms such as temporal or vertical-space partitioning may facilitate the coexistence of kiore and ship rats in Tuku Nature Reserve. The information gained here may inform pest management by determining the extent of the threat kiore and ship rats pose on the environment. Since I found both rats had broad isotopic niches, high intraspecific and seasonal variation, it is likely that these species will impact a variety of native species and can shift their diet with environmental changes, indicating that they would be able to persist in a variety of environments. Thus, pest management strategies should account for these broad and flexible niches by targeting a variety of environments for trap placements with more intensive trapping closer to vulnerable native species that these rats are likely to target as observed from my diet analysis
- …
