I was waiting for some other responses and looking forward to other
Hi
I was waiting for some other responses and looking forward to other thoughts
but here is my twopence worth:
The first question is how is your data structured? Note that in the 158
published data sets as mentioned by Cottenie (2005, Ecology Letters) only 8%
i.e.,neutral processes were the only structuring process in 8% of the
collected natural communities,.
I would go with the more classic interpretation. I am not sure what model you
intend to fit or the structure of your data. I have used 'R' but not this
particular procedure in my first link - the article may be of interest / use to
you especially if you use R and note not only includes the modelling of the
environmental factors but also included are certain interaction effects - be
careful of the number of constrained axes since you will find something which
may be there due to the extreme number added (they had 54 eigenvalues ...). But
it really is a good way to proceed with like data. Their example uses species
matrices with vascular plants; and environmental matrix with chemical variables
and slope matrices.
The link for Analysis of community ecology data in R by David Zelený is:
http://www.davidzeleny.net/anadat-r/doku.php/en:rda_cca
Hope it is of help.
For others interested a good article sort of describing why RDA over other
ordination methods is by Michael Palmer
http://ordination.okstate.edu/overview.htm
Regards,
Ling
Ling Huang
Sacramento City College
On Monday, May 26, 2014 2:08 PM, Alexandre Fadigas de Souza
alexso...@cb.ufrn.br wrote:
Dear friends,
I am thinking on the interpretation of the results of the variation
partitioning of community composition by means of RDA. Despite all drawbacks of
the approach, it continues as an important tool to access the global effects of
environmental factors and space on the variance of species abundances in
communities. However, I think there are two somehow different interpretations
of the results.
I would like to know what do you think about it, in order to make it clearer.
The more classic interpreation for significant pure environmental and pure
spatial effects (the most common result) is that the environmental effects
represent species sorting (SS) by abiotic factors (niche related) while the
spatial effects represent dispersal limitation, possibly linked to neutral
dynamics, aside non-measured abiotic factors.
In his review of these results, however, Cottenie (2005, Ecology Letters)
proposed a classification of matacommunities based on variation partitioning
results, and interpreted significant pure environmental + pure spatial
fractions as indicative of Species Sorting + Mass Efffects metacommunity
dynamics. Do you know why would it not be indicative of Species Sorting +
Neutral Dynamics? What would be the reasoning for the differentiation between
Mass effects and Neutral Dynamics?
My first thought was that the pure spatial component would be indicative of
dispersal limitation effects. This would be nearer neutrality than mass
effects, since mass effects represent the opposite of dispersal limitation,
wright? There is an overflow of dispersal not limitation.
Thank you very much in advance for any thoughts,
All the best,
Alexandre
Dr. Alexandre F. Souza
Professor Adjunto II, Departamento de Ecologia Universidade Federal do Rio
Grande do Norte (UFRN)
Caixa Postal 1524, Campus Universitario Lagoa Nova
CEP 59078-970 http://www.docente.ufrn.br/alexsouza Curriculo:
lattes.cnpq.br/7844758818522706
