ISJ =
___a___
a+b+c
Jaccard’s similarity index:
a = number of species in common between
the stands
b = number of species unique to the first
stand,
c = number of species unique to the second
stand.
Jaccard’s indices are based on presence/absence of
species that are shared between samples of vegetation and
species that are unique to each sample.
For Shannon index see the following
website:
It has examples of how to calculate!
http://www.mdsg.umd.edu/Education/biofilm/diverse.htm#3
Shannon-Wiener Index
This diversity measure came from information theory and
measures the order (or disorder) observed within a particular
system. In ecological studies, this order is characterized by the
number of individuals observed for each species in the sample plot
(e.g., biofilm on a plexiglass disc).
Similar to the Simpson index, the first step is to calculate Pi for
each category (e.g., species). Pi is the number of a given species
divided by the total number of organisms observed. You then
multiply this number by the log of the number. While you may use
any base, the natural log is commonly used (ln). The index is
computed from the negative sum of these numbers. In other words,
the Shannon-Wiener index is defined as:
H = -sum(Piln[Pi]) (natural log)
Why do you take the negative of the sum(Pilog[Pi])?
Since Pi is the proportion of a given category, its maximum value
is 1 and its minimum approaches 0. For any base, the log of 1 is 0
and the log of any value between 0 and 1 is a negative number. By
reversing the sign, the index becomes positive and is easier to
understand.
What are the minimum and maximum values for the
Shannon-Wiener index?
Minimum value: 0
Maximum value: log(1/# of categories)