vegan (version 1.8-1)

bioenv: Best Subset of Environmental Variables with Maximum (Rank) Correlation with Community Dissimilarities

Description

Function finds the best subset of environmental variables, so that the Euclidean distances of scaled environmental variables have the maximum (rank) correlation with community dissimilarities.

Usage

## S3 method for class 'default':
bioenv(comm, env, method = "spearman", index = "bray",
       upto = ncol(env), trace = FALSE, ...)
## S3 method for class 'formula':
bioenv(formula, data, ...)

Arguments

comm

Community data frame.

env

Data frame of continuous environmental variables.

method

The correlation method used in cor.

index

The dissimilarity index used for community data in vegdist.

upto

Maximum number of parameters in studied subsets.

formula, data

Model formula and data.

trace

Trace the advance of calculations

...

Other parameters passed to function.

Value

• The function returns an object of class bioenv with a summary method.

Details

The function calculates a community dissimilarity matrix using vegdist. Then it selects all possible subsets of environmental variables, scales the variables, and calculates Euclidean distances for this subset using dist. Then it finds the correlation between community dissimilarities and environmental distances, and for each size of subsets, saves the best result. There are $2^p-1$ subsets of $p$ variables, and an exhaustive search may take a very, very, very long time (parameter upto offers a partial relief).

The function can be called with a model formula where the LHS is the data matrix and RHS lists the environmental variables. The formula interface is practical in selecting or transforming environmental variables.

Clarke & Ainsworth (1993) suggested this method to be used for selecting the best subset of environmental variables in interpreting results of nonmetric multidimensional scaling (NMDS). They recommended a parallel display of NMDS of community dissimilarities and NMDS of Euclidean distances from the best subset of scaled environmental variables. They warned against the use of Procrustes analysis, but to me this looks like a good way of comparing these two ordinations.

Clarke & Ainsworth wrote a computer program BIO-ENV giving the name to the current function. Presumably BIO-ENV was later incorporated in Clarke's PRIMER software (available for Windows). In addition, Clarke & Ainsworth suggested a novel method of rank correlation which is not available in the current function.

References

Clarke, K. R & Ainsworth, M. 1993. A method of linking multivariate community structure to environmental variables. Marine Ecology Progress Series, 92, 205--219.

See Also

vegdist, dist, cor for underlying routines, isoMDS for ordination, procrustes for Procrustes analysis, protest for an alternative, and rankindex for studying alternatives to the default Bray-Curtis index.

Examples

# The method is very slow for large number of possible subsets.
# Therefore only 6 variables in this example.
data(varespec)
data(varechem)
sol <- bioenv(wisconsin(varespec) ~ log(N) + P + K + Ca + pH + Al, varechem)
sol
summary(sol)