





To whom it may concern,
I am having some problems about using MRPP or ADONIS function (vegan package).
I am running the 2 analysis with the aim of finding out if the composition of vegetation (forest and no forest) is changed from 1830 to 1990 over the same landscape.

Why the results from MRPP and ADONIS are different?
May some of you help me?

Many thanks

Federico

##########################################################

> mrpp.forest

Call:
mrpp(dat = dom.all.nt.pa, grouping = as.factor(forest.1830.sub & forest.1920.sub), distance = "jaccard") 

Dissimilarity index: jaccard 
Weights for groups:  n 

Class means and counts:

      FALSE  TRUE  
delta 0.8435 0.4211
n     272    3     

Chance corrected within-group agreement A: 0.003783 
Based on observed delta 0.8389 and expected delta 0.8421 

Significance of delta: 0.001 
Based on  999  permutations
-----------------------------------------------------------------------------------
> mrpp.grasses

Call:
mrpp(dat = dom.all.ag.pa, grouping = as.factor(grasses.1830.sub & grasses.1920.sub), distance = "jaccard") 

Dissimilarity index: jaccard 
Weights for groups:  n 

Class means and counts:

      FALSE  TRUE  
delta 0.7352 0.7885
n     486    203   

Chance corrected within-group agreement A: 0.002757 
Based on observed delta 0.7509 and expected delta 0.7529 

Significance of delta: 0.001 
Based on  999  permutations
---------------------------------------------------------------------------------------------
> adonis.forest

Call:
adonis(formula = dom.all.nt.pa ~ as.factor(forest.1830.sub & forest.1920.sub), distance = "jaccard") 

                                              Df SumsOfSqs MeanSqs F.Model      R2 Pr(>F)  
as.factor(forest.1830.sub & forest.1920.sub)   1     0.485 0.48517  1.6591 0.00604  0.074 .
Residuals                                    273    79.832 0.29242         0.99396         
Total                                        274    80.317                 1.00000         
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
---------------------------------------------------------------------------------------------
> adonis.grasses

Call:
adonis(formula = dom.all.ag.pa ~ as.factor(grasses.1830.sub & grasses.1920.sub), distance = "jaccard") 

                                                Df SumsOfSqs MeanSqs F.Model      R2 Pr(>F)    
as.factor(grasses.1830.sub & grasses.1920.sub)   1     1.274 1.27435  6.2078 0.00896  0.001 ***
Residuals                                      687   141.029 0.20528         0.99104           
Total                                          688   142.303                 1.00000           
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 

 		 	   		   		 	   		  
	[[alternative HTML version deleted]]

