RDA and linear dependence between variables

[a***@gmail.com]

Hi,

I would be most grateful for help regarding the redundancy analysis (RDA), since I must urgently answer the question to the journal editor. Sorry for my poor English and if the question emerges trivial.

The problem concerns the occurrence of bird communities in relation to some environmental variables. I performed RDA in Canoco. In twelve plots there were 49 species with abundance data, against four continuous environmental variables. The editor noted that RDA assumes linear dependence of the response and explanatory variables, and asked whether I have verified that my data are linearly dependent.

I'm not sure how to verify this dependence and if it's really necessary. I have reviewed several papers and did not found any good answer. Is that truth that each species should be treated a response variable? What about rare species? I did correlation matrix (in Statistica), most numerous species revealed a relationship close to linear, indeed, but not all of them. The log transformation does not help. Overall, I suppose that there may be a general error in the attempt, but I wonder where.

Thanks for help

Andrzej
(Poland)

[Rich Ulrich]

Post by a***@gmail.com
Hi,
I would be most grateful for help regarding the redundancy analysis (RDA), since I must urgently answer the question to the journal editor. Sorry for my poor English and if the question emerges trivial.
The problem concerns the occurrence of bird communities in relation to some environmental variables. I performed RDA in Canoco. In twelve plots there were 49 species with abundance data, against four continuous environmental variables. The editor noted that RDA assumes linear dependence of the response and explanatory variables, and asked whether I have verified that my data are linearly dependent.
I'm not sure how to verify this dependence and if it's really necessary. I have reviewed several papers and did not found any good answer. Is that truth that each species should be treated a response variable? What about rare species? I did correlation matrix (in Statistica), most numerous species revealed a relationship close to linear, indeed, but not all of them. The log transformation does not help. Overall, I suppose that there may be a general error in the attempt, but I wonder where.
Thanks for help
Andrzej
(Poland)

Even when we were a busy group, I don't think that we
had experts who were involved with ecological data.

What I discovered while looking up Correspondence
Analysis is a site that seems to build upon ecology, and
which includes many relevant techniques - Oklahoma State
University.

http://ordination.okstate.edu/overview.htm

That page has only a few comments on RDA, but maybe
they will help directly or indirectly.

[a***@gmail.com]

Post by Rich Ulrich

Post by a***@gmail.com
Hi,
I would be most grateful for help regarding the redundancy analysis (RDA), since I must urgently answer the question to the journal editor. Sorry for my poor English and if the question emerges trivial.
The problem concerns the occurrence of bird communities in relation to some environmental variables. I performed RDA in Canoco. In twelve plots there were 49 species with abundance data, against four continuous environmental variables. The editor noted that RDA assumes linear dependence of the response and explanatory variables, and asked whether I have verified that my data are linearly dependent.
I'm not sure how to verify this dependence and if it's really necessary. I have reviewed several papers and did not found any good answer. Is that truth that each species should be treated a response variable? What about rare species? I did correlation matrix (in Statistica), most numerous species revealed a relationship close to linear, indeed, but not all of them. The log transformation does not help. Overall, I suppose that there may be a general error in the attempt, but I wonder where.
Thanks for help
Andrzej
(Poland)

Even when we were a busy group, I don't think that we
had experts who were involved with ecological data.
What I discovered while looking up Correspondence
Analysis is a site that seems to build upon ecology, and
which includes many relevant techniques - Oklahoma State
University.
http://ordination.okstate.edu/overview.htm
That page has only a few comments on RDA, but maybe
they will help directly or indirectly.
--
Rich Ulrich

Thank you for this hint. The Ordination Webpage is really interesting. Actually, I sent my post also to that list, but there was no response, unfortunately.

Andrzej