diversity indexes (fwd)
Coral Health and Monitoring Program
coral at coral.aoml.noaa.gov
Thu Feb 29 14:43:14 EST 1996
This message, originally sent to owner-coral-list at reef.aoml.noaa.gov,
is forwarded herewith:
---------- Forwarded message ----------
Date: Wed, 13 Mar 1996 07:16:02 -0500 (EST)
From: James C. Hendee <hendee at aoml.noaa.gov>
To: coral at coral
Subject: RE: diversity indexes (fwd)
---------- Forwarded message ----------
Date: Wed, 13 Mar 1996 16:46:00 -0800 (PST)
From: John McManus <J.MCMANUS at cgnet.com>
To: owner-coral-list <owner-coral-list at reef.aoml.noaa.gov>
Subject: RE: diversity indexes
TO:coral list
In reply to Amorim (and for others who are interested) there are several
approaches to statistically comparing diversity indices. If you have data
leading to two indices, you can calculate a variance for each index and
conduct a t-test. The procedure is in:
Magurran, A.E. 1988. Ecological Diversity and its Measurement. Croom Helm,
London. 179 p.
A more powerful approach would be to use a randomization approach.
Randomization may become a standard way to do most statistical comparisons
in the future, but is not there yet, so it might require some programming.
Neither approach makes me comfortable about comparing diversities in two
areas or one area over time, because they do not account for geographic
variability in any straight-forward way. Instead, I prefer to take several
sample units of equal size in each of the two areas (or times) and treat the
diversity indices as if they were a variable such as "fish abundance per
transect", calculating mean diversities, variances on the mean, and doing
standard statistical tests.
However, this only works for transects of the same length and width, as
corrections for size are complicated. This will tell you if there is a
difference in diversity "per transect" between areas or times.
The pros and cons of using the Shannon versus other indices are covered in
Magurran's book, which is highly recommended. I like to define the Shannon
value as "diversity" and then to analyze the changes in diversity over time
or space in terms of changes in abundance, richness, species per 1,000
individuals and evenness (H'/log(s)). That way I identify a pattern and
then seek to explain it. Examples are found in our book "The Resource
Ecology of the Bolinao Coral Reef" which is unfortunately out of print, but
in the collections of some coral reef scientists. If you send us an
address, we can send you photocopies of the relevant pages. The whole book
is available as a photocopy from ICLARM for $17.50.
Sincerely,
Dr. John W. McManus
Program Leader, Aquatic Environments Program
Project Leader, ReefBase Project
International Center for Living Aquatic Resources Management (ICLARM)
205 Salcedo Street, Legaspi Village, Makati, Metro Manila 1229 Philippines
Tel. No. (63-2) 8180466/Fax No.: (63-2) 8163183
E-Mail: J.McManus at cgnet.com
----------
From: owner-coral-list
To: coral-list
Subject: diversity indexes
Date: Monday, March 11, 1996 10:40AM
Dear all,
I'm doing a research work on comparing coral reef fishes in two
areas, using a video camera.
What I need to know, urgently, is how to compare, statisticly,
diversity indexes to see if they are significant.
Are there any scientific papers on similar studies?
I would appreciate it if you would help me. Thanks!
Sorry for any duplication!
--
amorim
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