Re: NANFA-L-- Diversity Indicies

Todd D. Crail (tcrail at UTNet.UToledo.Edu)
Thu, 29 Sep 2005 12:44:56 -0400

Yeah IBI isn't going to work. I didn't describe my situation very well,
sorry about the argument there.

So if I'm understanding what I'm reading about Hill's, it will account for
the discrepantcy in the biomass? I'm just looking for a simple way to
compare multiple yet similar sites within a watershed, using the fish
community sampled as the response variable.

The problem I'm running into is something like this:

One of my sites consisted of:
green sunfish(1)
least darter(95)

If I caluculate Simpsons on that site alone, I get 1.15, in part, because
least darter are so proportionately more represented than other species when
you compare it to another replicate site:

fathead (1)

...which comes out 1.28.

The second site is more "diverse"? It's definately more even, but c'mmon!
And we also loose the fact the least darter is a large proportion of the
individuals found at the first site, and more aggrivatingly, is a SSC fish.
The whole diversity issue irons out when all the replicates are taken in
consideration, but I'd rather drive my point home with a hammer, rather than
some feather-like p value that doesn't make any sense to anyone besides the
0.05% I work with lol.

What I'd really like to do is find a way to compare each site against the
whole of the sample, where each replicate receives a score against the
whole. I would think there'd be some way to compare stream segments along a
gradient (perhaps by stream order?) but I guess everyone has been too busy
counting mayflies and snails they can't speciate to look at something easier
to identify, like fish.

I dunno. I dunno if this works for on-list traffic either. I guess I
rationalize it that if there isn't an easy way to compare parts of streams
by a response variable such as fish community, then the NANFA list is making
something useful and doesn't require understanding how greek symbols relate
to each other to figure out if part of a stream fares better than another
part of the same system. It sure seems can't voice my opinion here at
school... Apparently masters students are to only be seen and not heard. Oh
bondage... {obscure x-ray specs reference}

Thanks for your help and continued tolerance :)

----- Original Message -----
From: "Bruce Stallsmith" <fundulus at>
To: <nanfa-l at>
Sent: Thursday, September 29, 2005 10:48 AM
Subject: Re: NANFA-L-- Diversity Indicies

> For more statistically rigorous and informative index values, check out
> various Hill's diversity numbers, especially the second diversity number
> (N2), which is the inverse of Simpson's index. That N2 value gives you the
> number of very abundant species, which use can be argued for on a variety
> practical and theoretical grounds. I'm happy to hand out references
> off-line.
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