diversity indexes (fwd)

[Coral Health and Monitoring Program]

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