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Steven C. Walker
McMaster University
14Publications
10H-index
11.6kCitations
Publications 14
Newest
Published on Oct 1, 2016in Trends in Ecology and Evolution 15.94
David I. Warton33
Estimated H-index: 33
(University of New South Wales),
F. Guillaume Blanchet13
Estimated H-index: 13
(McMaster University)
+ 4 AuthorsFrancis K. C. Hui12
Estimated H-index: 12
(Australian National University)
The joint modelling of many variables in community ecology is a new and technically challenging area with many opportunities for future developments. The possibility of extending joint models to deal with imperfect detection has been highlighted by Beissinger et al. as an important problem worthy of further investigation [1]. We agree, and previously pointed to this potential extension as an outstanding question [2], alongside models that can estimate phylogenetic repulsion or attraction, nonlin...
7 Citations Source Cite
Published on Dec 1, 2015in Trends in Ecology and Evolution 15.94
David I. Warton33
Estimated H-index: 33
(University of New South Wales),
F. Guillaume Blanchet13
Estimated H-index: 13
(McMaster University)
+ 4 AuthorsFrancis K. C. Hui12
Estimated H-index: 12
(Australian National University)
Technological advances have enabled a new class of multivariate models for ecology, with the potential now to specify a statistical model for abundances jointly across many taxa, to simultaneously explore interactions across taxa and the response of abundance to environmental variables. Joint models can be used for several purposes of interest to ecologists, including estimating patterns of residual correlation across taxa, ordination, multivariate inference about environmental effects and envir...
157 Citations Source Cite
Published on Oct 7, 2015in Journal of Statistical Software 22.74
Douglas M. Bates30
Estimated H-index: 30
,
Martin Mächler15
Estimated H-index: 15
+ 1 AuthorsSteven C. Walker10
Estimated H-index: 10
Maximum likelihood or restricted maximum likelihood (REML) estimates of the parameters in linear mixed-effects models can be determined using the lmer function in the lme4 package for R. As for most model-fitting functions in R, the model is described in an lmer call by a formula, in this case including both fixed- and random-effects terms. The formula and data together determine a numerical representation of the model from which the profiled deviance or the profiled REML criterion can be evalua...
11.1k Citations Source Cite
Published on Oct 6, 2015
Douglas M. Bates30
Estimated H-index: 30
,
Martin Mächler15
Estimated H-index: 15
+ 1 AuthorsSteven C. Walker10
Estimated H-index: 10
151 Citations
Published on May 1, 2015in Plant Ecology 1.76
Steven C. Walker10
Estimated H-index: 10
(McMaster University)
Classical gradient analysis continues to be used to explore and test theories and models in community ecology. Yet the foundations of classical gradient analysis were developed at a time when computational power was limited, relative to current computational power. I argue that this history has left a lasting legacy on the field. Consequently, many gradient analyses do not to take advantage of current computer technology. Here I show how to use computationally intensive Markov-chain Monte Carlo ...
5 Citations Source Cite
Published on Jul 9, 2014
GuénardGuillaume8
Estimated H-index: 8
(Université de Montréal),
Peter C. von der Ohe25
Estimated H-index: 25
(Helmholtz Centre for Environmental Research - UFZ)
+ 2 AuthorsPierre Legendre82
Estimated H-index: 82
(Université de Montréal)
Direct estimation of species' tolerance to pesticides and other toxic organic substances is a combinatorial problem, because of the large number of species–substance pairs. We propose a statistical modelling approach to predict tolerances associated with untested species–substance pairs, by using models fitted to tested pairs. This approach is based on the phylogeny of species and physico-chemical descriptors of pesticides, with both kinds of information combined in a bilinear model. This biline...
15 Citations Source Cite
Published on Nov 13, 2012in Journal of Statistical Software 22.74
Steven C. Walker10
Estimated H-index: 10
,
GuénardGuillaume8
Estimated H-index: 8
+ 1 AuthorsPierre Legendre82
Estimated H-index: 82
Data frames are integral to R. They provide a standard format for passing data to model-fitting and plotting functions, and this standard makes it easier for experienced users to learn new functions that accept data as a single data frame. Still, many data sets do not easily fit into a single data frame; data sets in ecology with a so-called fourth- corner problem provide important examples. Manipulating such inherently multiple-table data using several data frames can result in long and difficu...
1 Citations Source Cite
Published on Jan 1, 2012in Biological Invasions 3.05
Laura L. Timms6
Estimated H-index: 6
(McGill University),
Steven C. Walker10
Estimated H-index: 10
(Université de Montréal),
Sandy M. Smith22
Estimated H-index: 22
(University of Toronto)
The gypsy moth is considered one of the most harmful invasive forest insects in North America. It has been suggested that gypsy moth may indirectly impact native caterpillar communities via shared parasitoids. However, the impact of gypsy moth on forest insect food webs in general remains unstudied. Here we assess such potential impacts by surveying forest insect food webs in Ontario, Canada. We systematically collected caterpillars using burlap bands at sites with and without histories of gypsy...
9 Citations Source Cite
Published on Nov 1, 2011in Ecological Monographs 7.83
Steven C. Walker10
Estimated H-index: 10
(University of Toronto),
Donald A. Jackson41
Estimated H-index: 41
(University of Toronto)
Ecology is inherently multivariate, but high-dimensional data are difficult to understand. Dimension reduction with ordination analysis helps with both data exploration and clarification of the meaning of inferences (e.g., randomization tests, variation partitioning) about a statistical population. Most such inferences are asymmetric, in that variables are classified as either response or explanatory (e.g., factors, predictors). But this asymmetric approach has limitations (e.g., abiotic variabl...
15 Citations Source Cite
Published on Feb 1, 2009in Ecology 4.62
Mark S. Poos10
Estimated H-index: 10
(University of Toronto),
Steven C. Walker10
Estimated H-index: 10
(University of Toronto),
Donald A. Jackson41
Estimated H-index: 41
(University of Toronto)
Functional diversity is an important concept in community ecology because it captures information on functional traits absent in measures of species diversity. One popular method of measuring functional diversity is the dendrogram-based method, FD. To calculate FD, a variety of methodological choices are required, and it has been debated about whether biological conclusions are sensitive to such choices. We studied the probability that conclusions regarding FD were sensitive, and that patterns i...
72 Citations Source Cite
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