546 research outputs found
Structured interactions as a stabilizing mechanism for competitive ecosystems
How large ecosystems can create and maintain the remarkable biodiversity we
see in nature is probably one of the biggest open question in science,
attracting attention from different fields, from Theoretical Ecology to
Mathematics and Physics. In this context, modeling the stable coexistence of
different species competing for limited resources is a particularly demanding
task. From the mathematical point of view, coexistence in competitive dynamics
can be achieved when dominance among species forms intransitive loops. However,
these relationships usually lead to species' densities neutrally cycling
without converging to a stable equilibrium and, although in recent years
several mechanisms have been proposed, models able to explain the robust
persistence of competitive ecosystems are lacking. Here we show that stable
coexistence in large communities can be achieved when the locality of
interactions is taken into account. We consider a simplified ecosystem where
individuals of each species lay on a spatial network and interactions are
possible only between nodes at a certain distance. Varying such distance allows
to interpolate between local and global competition. Our results demonstrate
that when two conditions are met: individuals are embedded in space and can
only interact with other individuals within a short distance, species coexist
reaching a stable equilibrium. On the contrary, when one of these ingredients
is missing large fluctuations and neutral cycles emerge.Comment: 7 pages, 5 figure
Competitive intransitivity, population interaction structure, and strategy coexistence
Sherpa Romeo green journal. Permission to archive accepted author manuscriptIntransitive competition occurs when competing strategies cannot be listed in a hierarchy, but rather
form loops – as in the game Rock-Paper-Scissors. Due to its cyclic competitive replacement, competitive
intransitivity promotes strategy coexistence, both in Rock-Paper-Scissors and in higher-richness communities. Previous work has shown that this intransitivity-mediated coexistence is strongly
influenced by spatially explicit interactions, compared to when populations are well mixed. Here, we
extend and broaden this line of research and examine the impact on coexistence of intransitive
competition taking place on a continuum of small-world networks linking spatial lattices and regular
random graphs. We use simulations to show that the positive effect of competitive intransitivity on
strategy coexistence holds when competition occurs on networks toward the spatial end of the
continuum. However, in networks that are sufficiently disordered, increasingly violent fluctuations in
strategy frequencies can lead to extinctions and the prevalence of monocultures. We further show that
the degree of disorder that leads to the transition between these two regimes is positively dependent
on population size; indeed for very large populations, intransitivity-mediated strategy coexistence may
even be possible in regular graphs with completely random connections. Our results emphasize the
importance of interaction structure in determining strategy dynamics and diversity
Evolutionary Algorithms for
Many real-world problems involve two types of problem difficulty: i) multiple, conflicting objectives and ii) a highly complex search space. On the one hand, instead of a single optimal solution competing goals give rise to a set of compromise solutions, generally denoted as Pareto-optimal. In the absence of preference information, none of the corresponding trade-offs can be said to be better than the others. On the other hand, the search space can be too large and too complex to be solved by exact methods. Thus, efficient optimization strategies are required that are able to deal with both difficulties. Evolutionary algorithms possess several characteristics that are desirable for this kind of problem and make them preferable to classical optimization methods. In fact, various evolutionary approaches to multiobjective optimization have been proposed since 1985, capable of searching for multiple Paretooptimal solutions concurrently in a single simulation run. However, in spite of this variety, there is a lack of extensive comparative studies in the literature. Therefore, it has remained open up to now
New Algorithms for Fast and Economic Assembly: Advances in Transcriptome and Genome Assembly
Great efforts have been devoted to decipher the sequence composition of
the genomes and transcriptomes of diverse organisms. Continuing advances in
high-throughput sequencing technologies have led to a decline in associated
costs, facilitating a rapid increase in the amount of available genetic data. In
particular genome studies have undergone a fundamental paradigm shift where
genome projects are no longer limited by sequencing costs, but rather by
computational problems associated with assembly. There is an urgent demand
for more efficient and more accurate methods. Most recently, “hybrid”
methods that integrate short- and long-read data have been devised to address
this need. LazyB is a new, low-cost hybrid genome assembler. It starts from a
bipartite overlap graph between long reads and restrictively filtered short-read
unitigs. This graph is translated into a long-read overlap graph. By design,
unitigs are both unique and almost free of assembly errors. As a consequence,
only few spurious overlaps are introduced into the graph. Instead of the more
conventional approach of removing tips, bubbles, and other local features,
LazyB extracts subgraphs whose global properties approach a disjoint union of
paths in multiple steps, utilizing properties of proper interval graphs. A
prototype implementation of LazyB, entirely written in Python, not only yields
significantly more accurate assemblies of the yeast, fruit fly, and human
genomes compared to state-of-the-art pipelines, but also requires much less
computational effort. An optimized C++ implementation dubbed MuCHSALSA
further significantly reduces resource demands.
Advances in RNA-seq have facilitated tremendous insights into the role of
both coding and non-coding transcripts. Yet, the complete and accurate
annotation of the transciptomes of even model organisms has remained elusive.
RNA-seq produces reads significantly shorter than the average distance
between related splice events and presents high noise levels and other biases
The computational reconstruction remains a critical bottleneck.
Ryūtō implements an extension of common splice graphs facilitating the integration
of reads spanning multiple splice sites and paired-end reads bridging distant
transcript parts. The decomposition of read coverage patterns is modeled as a
minimum-cost flow problem. Using phasing information from multi-splice and
paired-end reads, nodes with uncertain connections are decomposed step-wise
via Linear Programming.
Ryūtōs performance compares favorably with
state-of-the-art methods on both simulated and real-life datasets. Despite
ongoing research and our own contributions, progress on traditional single
sample assembly has brought no major breakthrough. Multi-sample RNA-Seq
experiments provide more information which, however, is challenging to utilize
due to the large amount of accumulating errors. An extension to Ryūtō
enables the reconstruction of consensus transcriptomes from multiple RNA-seq
data sets, incorporating consensus calling at low level features. Benchmarks
show stable improvements already at 3 replicates.
Ryūtō outperforms competing approaches, providing a better and user-adjustable
sensitivity-precision trade-off. Ryūtō consistently improves assembly on
replicates, demonstrable also when mixing conditions or time series and for
differential expression analysis. Ryūtōs approach towards guided assembly is
equally unique. It allows users to adjust results based on the quality of the
guide, even for multi-sample assembly.:1 Preface
1.1 Assembly: A vast and fast evolving field
1.2 Structure of this Work
1.3 Available
2 Introduction
2.1 Mathematical Background
2.2 High-Throughput Sequencing
2.3 Assembly
2.4 Transcriptome Expression
3 From LazyB to MuCHSALSA - Fast and Cheap Genome Assembly
3.1 Background
3.2 Strategy
3.3 Data preprocessing
3.4 Processing of the overlap graph
3.5 Post Processing of the Path Decomposition
3.6 Benchmarking
3.7 MuCHSALSA – Moving towards the future
4 Ryūtō - Versatile, Fast, and Effective Transcript Assembly
4.1 Background
4.2 Strategy
4.3 The Ryūtō core algorithm
4.4 Improved Multi-sample transcript assembly with Ryūtō
5 Conclusion & Future Work
5.1 Discussion and Outlook
5.2 Summary and Conclusio
Proceedings of Mathsport international 2017 conference
Proceedings of MathSport International 2017 Conference, held in the Botanical Garden of the University of Padua, June 26-28, 2017.
MathSport International organizes biennial conferences dedicated to all topics where mathematics and sport meet.
Topics include: performance measures, optimization of sports performance, statistics and probability models, mathematical and physical models in sports, competitive strategies, statistics and probability match outcome models, optimal tournament design and scheduling, decision support systems, analysis of rules and adjudication, econometrics in sport, analysis of sporting technologies, financial valuation in sport, e-sports (gaming), betting and sports
September 8, 2016
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