Forum: help

RE: DCA using indicator values other than Ellenberg's [ Reply ] By: Oksana Abduloieva on 2017-02-28 09:11	[forum:43910]
Thank you!

RE: DCA using indicator values other than Ellenberg's [ Reply ]
By: David Zeleny on 2017-02-27 15:47

[forum:43908]

Dear Oksana,

DCA will be the same in all cases - DCA is an indirect ordination calculated from species composition data, and the use of Ellenberg (or Didukh) indicator values have no effect on calculation. What is happening is that weighted mean of indicator values is post hoc (after the calculation of DCA is finished) projected onto ordination diagram, by mean of regression with ordination axes. If you use constrained (direct) ordination (like RDA or CCA), in which environmental variables (here mean indicator values) get directly into ordination, than resulting ordination would be different for mean Ellenberg and mean Didukh values (since in constrained ordination the environmental variables directly enter the calculation). However, since mean Ellenber values are derived from species composition (because they are weighted by species presences or abundances in samples), mean Ellenberg (or other) indicator values cannot be used as explanatory in constrained ordination.

All the best

David

DCA using indicator values other than Ellenberg's [ Reply ]
By: Oksana Abduloieva on 2017-02-22 22:02

[forum:43907]

DCA_plots.docx (6) downloads

I get the same DCA plots and DCA summary using both Ellenberg's and other indicator values through JUICE - Ordinations - R-project - DCA. In particular, I use Didukh's indicator scales available at JUICE web-site. Initiation of the scales runs. Calculation for releves - add values to short headers. Head - add short headers to header data. In DCA analysis calculation window: environmental variables - in "Environmental vectors" check required headers. Scales are different, resulted plots are the same (example is in the attached file with plots). Maybe I understand DCA in wrong way?