Tag Archives: R

اعتبارسنجی متقاطع مکانی در مدلسازی توزیع گونه‌‌ها

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نویسنده: روزبه وَلَوی

This post is available in English

مدلسازی توزیع گونه‌ها به تخمین و برآورد ارتباط بین مجموعه‌ای از نقاط حضور گونه با متغیرهای زیست‌محیطی مرتبط می پردازد. یکی از مراحل اساسی این فرایند، ارزیابی قدرت مدل برای پیش­بینی مکان‌هایی است که احتمال حضورگونه در آنجا وجود دارد. این کار اغلب با ارزیابی پیش­بینی انجام شده در مجموعه‌ای ازنقاط که در فرآیند مدلسازی مورد استفاده قرار نگرفته اند (نقاط آزمایشی) صورت می‌گیرد.

تقسیم تصادفی داده‌های حضور گونه به نقاط آزمایشی و آموزشی

تقسیم تصادفی داده‌های حضور گونه به نقاط آزمایشی و آموزشی

مطالعات پیشین بر این نکته تاکید دارند که به منظور ارزیابی معتبر، نقاط آزمایشی باید مستقل از نقاط آموزشی باشند، این درحالیست که داده مستقل واقعی به ندرت در دسترس می باشد. به همین دلیل، در فرایند مدلسازی معمولا داده‌های موجود را به دو قسمت داده‌های آموزشی (برای کالیبره کردن مدل) و داده های آزمایشی (برای ارزیابی دقت مدل) تقسیم می‌کنند، این استراتژی می‌تواند چند قسمتی هم باشد (برای مثال اعتبارسنجی متقاطع یا cross-validation). از آنجاییکه این تقسیم بندی معمولا بصورت تصادفی انجام می‌شود، بنابراین گاهی اوقات نقاط آزمایشی در فواصل نزدیک به نقاط آموزشی قرار می‌گیرند. شکل زیر این مساله را به خوبی نشان می دهد که در آن نقاط آزمایشی به رنگ قرمز و نقاط آموزشی آبی هستند. اما آیا این مساله می‌تواند مشکلی ایجاد کند؟ Continue reading →

2017 Robert May Prize Winner: Jonathan Henshaw

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The Robert May Prize is awarded annually for the best paper published in Methods in Ecology and Evolution by an Early Career Researcher. We’re delighted to announce that the 2017 winner is Jonathan Henshaw, for his article ‘A unified measure of linear and nonlinear selection on quantitative traits‘.

The standard approach to quantifying natural selection, developed by Lande and Arnold, does not allow for comparable metrics between linear (i.e. selection on the mean phenotype) and nonlinear (i.e. selection on all other aspects of the phenotypic distribution, including variance and the number of modes) selection gradients. Jonathan Henshaw’s winning submission provides the first integrated measure of the strength of selection that applies across qualitatively different selection regimes (e.g. directional, stabilizing or disruptive selection). Continue reading →

2016 Robert May Prize Winner: Gabriella Leighton

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The Robert May Prize is awarded annually for the best paper published in Methods in Ecology and Evolution by an Early Career Researcher. We’re delighted to announce that the 2016 winner is Gabriella Leighton, for her article ‘Just Google it: assessing the use of Google Images to describe geographical variation in visible traits of organisms‘.

‘Just Google it’ marks an important step in converting ecology to an armchair science. Many species (e.g. owls, hawks, bears) are difficult, time-consuming, expensive and even dangerous to observe. It would be a lot easier if we didn’t have to spend time, energy and risk lives having to observe organisms in the field! Continue reading →

Issue 8.2

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Issue 8.2 is now online!

The February issue of Methods is now online!

This issue contains four(!) Applications articles and two Open Access articles. These six papers are freely available to everyone – no subscription required.

– Earth Mover’s Distance: The Earth Mover’s Distance (or EMD) is a method commonly used in image retrieval applications. The authors of this paper propose its use to calculate similarity in space use in the framework of movement ecology. This will be helpful for many questions regarding behavioural ecology, wildlife management and conservation.

– warbleR: The R package warbleR is a new package for the analysis of animal acoustic signal structure. It offers functions for downloading avian vocalisations from the open-access online repository Xeno-Canto, displaying the geographic extent of the recordings, manipulating sound files, detecting acoustic signals or importing detected signals from other software, and much more.

– meteR: The open-source R package, meteR directly calculates all of Maximum entropy theory of ecology’s (METE’s) predictions from a variety of data formats; automatically handles approximations and other technical details; and provides high-level plotting and model comparison functions to explore and interrogate models.

– Noise Egg: The Noise Egg is a device that can produce a low-frequency sound, which can be used as an experimental source of noise both in aquaria and in the field. It was developed to study the effects of noise on communication and behaviour in small aquatic animals; however, it could be used for other purposes, such as testing the propagation of certain frequencies in shallow-water habitats.

Continue reading →

Issue 8.1

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Issue 8.1 is now online!

The January issue of Methods is now online!

All of the articles in this month’s issue of Methods in Ecology and Evolution are free for the whole year. You will not need a subscription to access or download any of them throughout 2017.

Our first issue of this year contains three Applications articles and two Open Access articles. These five papers will be freely available permanently.

– CDMetaPOP: Cost–Distance Meta-POPulation provides a novel tool for questions in landscape genetics by incorporating population viability analysis, while linking directly to conservation applications.

– Rphylopars: An R implementation of PhyloPars, a tool for phylogenetic imputation of missing data and estimation of trait covariance across species (phylogenetic covariance) and within species (phenotypic covariance). Rphylopars provides expanded capabilities over the original PhyloPars interface including a fast linear-time algorithm, thus allowing for extremely large data sets (which were previously computationally infeasible) to be analysed in seconds or minutes rather than hours.

– ggtree: An R package that provides programmable visualisation and annotation of phylogenetic trees. ggtree can read more tree file formats than other software and allows colouring and annotation of a tree by numerical/categorical node attributes, manipulating a tree by rotating, collapsing and zooming out clades, highlighting user selected clades or operational taxonomic units and exploration of a large tree by zooming into a selected portion.

Continue reading →

Issue 7.12

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Issue 7.12 is now online!

The final 2016 issue of Methods is now online!

This month’s issue contains four Applications articles and two Open Access articles, all of which are freely available.

– iNEXT: The R package iNEXT (iNterpolation/EXTrapolation) provides simple functions to compute and plot the seamless rarefaction and extrapolation sampling curves for the three most widely used members of the Hill number family (species richness, Shannon diversity and Simpson diversity).

– camtrapR: A new toolbox for flexible and efficient management of data generated in camera trap-based wildlife studies. The package implements a complete workflow for processing camera trapping data.

– rotl: An R package to search and download data from the Open Tree of Life directly in R. It uses common data structures allowing researchers to take advantage of the rich set of tools and methods that are available in R to manipulate, analyse and visualize phylogenies.

– Fluctuating-temperature chamber: A design for economical, programmable fluctuating-temperature chambers based on a relatively small commercially manufactured constant temperature chamber modified with a customized, user-friendly microcontroller.

Continue reading →

Issue 7.11

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Issue 7.11 is now online!

The November issue of Methods is now online!

This month’s issue contains four Applications articles and two Open Access articles, all of which are freely available.

– moveHMM: This R package allows ecologists to process GPS tracking data into series of step lengths and turning angles, and to fit a hidden Markov model to these data, allowing, in particular, for the incorporation of environmental covariates.

– BORIS: An open-source and multiplatform standalone program that allows a user-specific coding environment to be set for a computer-based review of previously recorded videos or live observations. Being open to user-specific settings, the program allows a project-based ethogram to be defined that can then be shared with collaborators, or can be imported or modified.

– inbreedR: An R package that provides functions to measure variance in inbreeding – through the strength of correlation in heterozygosity across marker loci – based on microsatellite and SNP markers with associated P-values and confidence intervals. Within the framework of Heterozygosity–fitness correlation theory, inbreedR also estimates the impact of inbreeding on marker heterozygosity and fitness.

– Terrestrial Precipitation Analysis: This package is comprised of the Precipitation Trends (P-Trend), Precipitation Attributes (P-Att) and Precipitation Manipulation (P-Man) tools. Combined, these web tools allow researchers to easily calculate fundamental precipitation statistics for past, present and projected future precipitation regimes for any terrestrial location in the world.

Continue reading →

Issue 7.10

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Issue 7.10 is now online!

The October issue of Methods is now online!

This month’s issue contains three Applications articles and two Open Access articles, all of which are freely available.

– CODYN: New analytical tools applied to long-term data demonstrate that ecological communities are highly dynamic over time. The R package, library(“codyn”), helps ecologists implement these tools and gain insi–ghts into ecological community dynamics.

– Geometric Morphometrics: A tool for the R statistical environment that optimises the smoothing procedure for 3D surfaces used in Geometric Morphometrics.

– TRAPPER: Open source, multi-user software that facilitates analysis of videos and images, provides spatial filtering and web-mapping, allows flexible implementation of specific data collection protocols, and supports data re-use and (re)discovery.

Continue reading →

Making Your Research Reproducible with R

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Post provided by Laura Graham

tweetReproducible research is important for three main reasons. Firstly, it makes it much easier to revisit a project a few months down the line, for example when making revisions to a paper which has been through peer review.

Secondly, it allows the reader of a published article to scrutinise your results more easily – meaning it is easier to show their validity. For this reason, some journals and reviewers are starting to ask authors to provide their code.

Thirdly, having clean and reproducible code available can encourage greater uptake of new methods. It’s much easier for users to replicate, apply and improve on methods if the code is reproducible and widely available

Throughout my PhD and Postdoctoral research, I have aimed to ensure that I use a reproducible workflow and this generally saves me time and helps to avoid errors. Along the way I’ve learned a lot through the advice of others, and trial and error. In this post I have set out a guide to creating a reproducible workflow and provided some useful tips. Continue reading →

Issue 7.9

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Issue 7.9 is now online!

The September issue of Methods is now online!

This month’s issue contains two Applications articles and three Open Access articles, all of which are freely available.

– Arborist Throw-Line Launcher: A cost-effective and simple alternative for collecting leaves and seeds from tall trees. The authors have also provided some tutorial videos on YouTube.

– ctmm: An R package which implements all of the continuous-time stochastic processes currently in use in the ecological literature and couples them with powerful statistical methods for autocorrelated data adapted from geostatistics and signal processing.

Continue reading →