[R-sig-eco] null model selection in functional diversity analysis

2014-10-23 Thread Marc Taylor
Dear r-sig-ecology listers, I am involved in a study whose objective is the see if there relationships between the functional diversity of the fish community and environmental factors of the sample site for a number of sites in a bounded environment. Specifically, we are looking at the parameters

[R-sig-eco] variance partitioning: vegan

2014-10-23 Thread Martin Weiser
Dear friends, I have just looked at vegan:::varpart2, and it seems to me that in estimation of degrees of freedom for adjusted R2 calculation, it just uses number of columns in the constraining matrix/dataframe. Am I right? Is this appropriate if the constraining dataframe involves factors with

Re: [R-sig-eco] null model selection in functional diversity analysis

2014-10-23 Thread Zoltan Botta-Dukat
Dear Marc, Try the permutation of trait values! Such permutation does not change any of the patterns that you mentioned and probably wanted to be constrained. On the other hand, it removes the correlation between traits and environment, and also correlation between traits and abundance.

Re: [R-sig-eco] Regression with few observations per factor level

2014-10-23 Thread Jari Oksanen
On 23/10/2014, at 18:17 PM, Gavin Simpson wrote: On 22 October 2014 17:24, Chris Howden ch...@trickysolutions.com.au wrote: A good place to start is by looking at your residuals to determine if the normality assumptions are being met, if not then some form of glm that correctly models the

Re: [R-sig-eco] Logistic regression with 2 categorical predictors

2014-10-23 Thread Gavin Simpson
This all looks bogus to me; you've fit the data perfectly by fitting a saturated model - there are no residual degrees of freedom and (effectively) zero residual deviance. Things are clearly amiss because you have huge standard errors. You have 24 data points and fit a model with 23 coefficient

Re: [R-sig-eco] Regression with few observations per factor level

2014-10-23 Thread Gavin Simpson
I think there are actually 4 data points per level of some factor (after seeing some of the other no-threaded emails - why can't people use emails that preserve threads?**); but yes, either way this is a small data set and trying to decide if residuals are normal or not is going to be nigh on

Re: [R-sig-eco] mvabund-interprating the uni.test

2014-10-23 Thread David Warton
Hi Kendra, Thanks for the question. It is great to see you looking at the relative size/significance of univariate tests as a way to gauge which species most strongly respond to some environmental gradient (/treatment) - this is a much more reliable way to do things than using something like

Re: [R-sig-eco] mvabund-interprating the uni.test

2014-10-23 Thread David Warton
Hi Kendra, Which values are in uni.test depends which test statistic you choose to use (in the test argument) - the default is log-likelihood ratio statistics (not sum-of-LR, but the original LR's that later get summed to make a multivariate statistic). For something in the output that tells