Re: [R-sig-eco] hierarchical partitioning: type of R-squared

2009-10-14 Thread Howe, Eric (MNR)
Good day Clement, and R users, I've used the hier.part package. I think that conceptually, if the form of relationship with the dependent variable differs among independent variables, hier.part won't provide unbiased results. Different samples from the same population should yield the same est

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Matthew Landis
Dear list - Apologies if this is not a repost. I sent it the first time in html format inadvertently and it hasn't shown up. Corrado - I meant to refer to a regression model - presumably you are going to build a regression model of sorts (although multivariate because of all the species) to s

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Matthew Landis
That's a really great paper, but if memory serves, it focuses on univariate regression models. Useful in this context for exploring the responses of a single species at a time, instead of a multivariate approach considering multiple species simultaneously. By the way, I have the author as Dor

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Marcelino de la Cruz
I would recomend the paper of Dortman et al. (Ecography 30: 609628, 2007). This reviews many available spatial statistical methods to take spatial autocorrelation into account in tests of statistical significance. From their abstract: "Here, we describe six different statistical approaches

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Martin Alejandro Piazzon de Haro
Dear friends, I found this thread very useful, so I wanted to apport something, Corrado, you asked for some references about PCNM, here is what i found: Borcard, D. and Legendre, P. 2002. All-scale spatial analysis of ecological data by means of principal coordinates of neighbour matrices. Ecolog

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Corrado
Dear Matthew, thanks for your kind answer! The first approach you describe is the one I have been looking at until now. I am puzzled about the second one: I do not really understand it. What model are you talking about, when you say "incorporate the spatial variation in the model"? At the mome

Re: [R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Matthew Landis
Corrado: The simplest way would be to take a subset of sites to maximize the distance between them. Say, choose 400 sites evenly spread over the study area. That would minimize autocorrelation to the greatest extent possible, but you would be throwing away data. The second thing you could

Re: [R-sig-eco] using two distance metrices in formula

2009-10-14 Thread Marcelino de la Cruz
Still another aproach would be Generalized Dissimilarity Modelling [see Ferrier et al. in Diversity and Distributions (2007) 13: 252-264]. Basicallly, a MRM improved to account for non-linearity in the data. From its webpage (http://www.biomaps.net.au/gdm/):"The only version of the software cu

Re: [R-sig-eco] using two distance metrices in formula

2009-10-14 Thread Gavin Simpson
On Wed, 2009-10-14 at 09:13 +0200, Maarten de Groot wrote: > Dear Jens, > > As far as I understood you are looking for the influence of one distance > matrix on another. (Please correct me if I am wrong) Than the following > reference might be useful: > > ter Braak, C. J. F. and Schaffers, A. P

[R-sig-eco] Reducing spatial autocorrelation

2009-10-14 Thread Corrado
Dear friends, I have a large matrix of species (first 1100 columns) and environmental variables (last 36 columns) for approx 2000 sites. The distance between sites varies. Some sites are near to each other, others are far. I would like to select a subset of N sites (for example: 400 sites) wi

[R-sig-eco] hierarchical partitioning: adaptation and interpretation

2009-10-14 Thread Clément Tisseuil
Dear R users, In the hier.part package, hierarchical partitioning is built upon a GLM (generalized linear model) framework to assess the independent and joint effect from a set of predictors onto a single quantitative response variable. In this context, the joint and independent effect from each f

Re: [R-sig-eco] using two distance metrices in formula

2009-10-14 Thread Maarten de Groot
Dear Jens, As far as I understood you are looking for the influence of one distance matrix on another. (Please correct me if I am wrong) Than the following reference might be useful: ter Braak, C. J. F. and Schaffers, A. P. 2004: Co-correspondence analysis: a new ordination method to relate

Re: [R-sig-eco] using two distance metrices in formula

2009-10-14 Thread Jens Oldeland
Dear Sarah, Jari and Peter, let me summarize what has been written so far 1) Jari said that: dbRDA needs rectangular data on right hand side of the formula --> dist.matrix on RHS leads to a lack of independence *no optimal solution* 2) Sarah suggests *MRM * 3) Peter suggests *Monmonier's maxi