Description Usage Arguments Details Value Author(s) References See Also Examples
The function finds two kinds of Hill indices of Beta diversity and tries to scale the gradient to constant Hill index 2 by segments.
1 2 3 4 |
veg |
Community data matrix. |
grad |
Environmental gradient. |
cycles |
Number of Hill scaling cycles in rescaling. |
freq.lim |
Frequency limit for including species. |
which |
Plots for indices 1 and 2. |
xlab |
Label for graphs. If missing, gradient name used. |
x |
A |
... |
Other graphical parameters. |
Mark Hill (1979) suggested two indices of Beta diversity:
Mean width of species responses, measured as weighted standard deviation of gradient values.
Weighted variance of species scores within a site.
Hill & Gauch (1980) discuss only the former index, but the program
decorana
uses only the second index.
Function betahill
calculates both indices for all sample plots. In
addition, the function smooths these on 20 segments along the
gradient, using the same algorithm as decorana
(Hill 1979, Hill & Gauch 1980).
Function hillscale
rescales the gradient by segments using Hill
index 2 (weighted variance of species scores) following as faithfully
as possible the rescaling algorithm in decorana
.
However, the function evaluates Hill index 1 (mean weighted sd of
species), unlike decorana
.
The major difference is that decorana
scales a
correspondence analysis axis where site scores are direct weighted
averages of species scores. Function hillscale
uses original
gradient values, but finds the species scores as weighted averages of
gradient values, and expands the species scores that they have the
same weighted variance as the species scores would have in
correspondence analysis. If a correspondence analysis axis is given as
a gradient, same species scores will be found as in
decorana
. Another major difference is that
decorana
never rescales site scores. It rescales
species scores instead, and always finds the site scores as direct
weighted averages of species scores. Function hillscale
rescales gradients. This difference is so significant that a rescaled
correspondence analysis axis will be different in hillscale
and
decorana
.
Both functions return an object of class "hillscale"
with
following items:
grad |
Rescaled gradient in |
Hill.1 |
Hill index 1 (mean weighted sd). |
Hill.2 |
Hill index 2 (weihted variance of species scores). |
zv1 |
The smoothed values of Hill.1 on 20 segments. |
zv2 |
The smoothed values of Hill.2 on 20 segments. |
rug |
21 rug tics equally distributed on the original gradient. |
cycles |
The number of rescaling cycles. |
gradname |
The name of the gradient variable. |
Call |
The function call. |
Jari Oksanen
Hill, M.O. (1979) DECORANA: a FORTRAN program for detrended correspondence analysis and reciprocal averaging. Cornell University, Ithaca, NY.
Hill, M.O. & Gauch, J.G. (1980) Detrended correspondence analysis: an improved ordination technique. Vegetatio 42, 47-58.
betadiversity
, gradscale
,
decorana
.
1 | ## None yet (no suitable data in the package)
|
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