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
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