1,720,972 research outputs found
Assessing the performance of common landscape connectivity metrics using a virtual ecologist approach
No full textDue to increasing habitat fragmentation and concern about its ecological effects, there has been an upsurge in the use of landscape connectivity estimates in conservation planning. Measuring connectivity is challenging, resulting in a limited understanding of the efficacy of connectivity estimation techniques and the conditions under which they perform best. We evaluated the performance of four commonly used connectivity metrics – Euclidean distance; least-cost paths (LCP) length and cost; and circuit theory's resistance distance – over a variety of simulated landscapes. We developed an agent-based model simulating the dispersal of individuals with different behavioural traits across landscapes varying in their spatial structure. The outcomes of multiple dispersal attempts were used to obtain ‘true' connectivity. These ‘true' connectivity measures were then compared to estimates generated using the connectivity metrics, employing the simulated landscapes as cost-surfaces. The four metrics differed in the strength of their correlation with true connectivity; resistance distance showed the strongest correlation, closely followed by LCP cost, with Euclidean distance having the weakest. Landscape structure and species behavioural attributes only weakly predicted the performance of resistance distance, LCP cost and length estimates, with none predicting Euclidean distance's efficacy. Our results indicate that resistance distance and LCP cost produce the most accurate connectivity estimates, although their absolute performance under different conditions is difficult to predict. We emphasise the importance of testing connectivity estimates against patterns derived from independent data, such as those acquired from tracking studies. Our findings should help to inform a more refined implementation of connectivity metrics in conservation management
Metacommunity structure and connectivity in dendritic ecological networks
No full textMany freshwater fish communities are declining globally, one of the primary causes of which is changes to
connectivity regimes. Connectivity strongly influences the ability of organisms to move around the landscape. In
riverine ecosystems, network topology and spatio-temporal environmental factors, such as flow variability and the
presence of barriers, determine connectivity. Furthermore, connectivity loss and processes such as climate change
do not influence biodiversity independently but will likely affect populations and communities synergistically.
Consequently, my thesis was motivated by the need to improve our understanding of freshwater fish population
and community dynamics in the face of changing connectivity and environmental regimes. In this thesis I aim
to address some of the knowledge gaps in these areas by applying the theoretical principles of metacommunity
ecology in conjunction with graph-theoretic methods.
First, I analysed the utility of graph-theoretic metrics for quantitatively describing simulated and real dendritic
ecological networks, finding that node scale metrics do not respond in a predictable way to algorithm input
parameters and that simulated networks are topologically different to real rivers regarding node metrics.
I then used a discrete-time logistic growth metacommunity model to analyse the role of spatial and temporal
functional connectivity in determining patterns of local species richness in freshwater fish metacommunities. The
results of this modelling suggest that: i) in dendritic ecological networks environmental spatial structure can
determine how communities respond to disturbance; ii) the effect of spatial loss of connectivity on local species
richness is determined by network topology and where richness is being measured; and iii) increasing temporal
autocorrelation in connectivity results in increasing temporal autocorrelation in patch occupancy.
Finally, I examined how intercatchment connectivity can affect extinction risk via source-sink dynamics, using
the upokororo (Prototroctes oxyrhynchus) as a case-study. I gathered historical data on the species to recreate a
distribution map for the species and to predict a likely extinction horizon. I then modelled the species’ population
dynamics to show that by accounting for amphidromous dispersal it is possible to explain how the species may
have gone extinct under relatively light harvesting pressure.
Overall, I conclude network topology and functional connectivity affect patterns of persistence and species
richness in their own right. Further, the effects of other drivers of population and community dynamics, such as
environmental variability can depend on underlying connectivity conditions
Through space and time: novel methods to prioritise management actions for invasive species
No full textSystematic eradication techniques were developed during the twentieth century to stem the negative impacts of invasive mammals and to facilitate restoration of island communities. Eradication projects have increased demonstrably in size, scope, and complexity over the last forty years and are now a principal conservation intervention on islands globally. Conservation practitioners are now setting their sights on projects with unprecedented levels of biogeographical and social complexity due to their potential for substantial conservation gains. However, the successful outcome of these projects is not guaranteed due to the high risk of reinvasion and often complex social structure. In this thesis, I investigate novel analytical techniques to prioritise the implementation of management actions for invasive species so that conservation practitioners can maximise the probability of restoring threatened island communities. I use New Zealand’s Predator Free 2050 programme as the context for this research.
Following a brief introduction (Chapter 1), I solve a strategic issue associated with where invasive species eradications should be conducted given limited time resources. I first (Chapter 2) quantify the underlying structure of insular isolation measures to understand how they mechanistically drive island biogeographical patterns. The measures synthesised in this chapter function as proxies for reinvasion, which represents one of the most-limiting factors behind eradication success. I then (Chapter 3) take these findings, along with metrics describing social complexity, to temporally prioritise eradications in New Zealand using statistical tools developed for survival analysis. These results can be used to determine whether a conservation priority should be selected for intervention immediately or in the future. I then (Chapter 4) solve a tactical issue associated with determining appropriate management actions for the New Zealand mainland given a suite of potentially suitable options. This prioritising model employs a machine learning technique to predict where, within the landscape, different management methods have the highest probability of being implemented. These results can be used to create a contiguous management network across large and heterogeneous areas.
The next-step in invasive species management requires that conservation action takes place in large and complex areas. This research gives practitioners tools to help them determine the feasibility of proposed management plans at unprecedented spatiotemporal scales
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
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