The system I'm working with is a comparison of habitat in ditches and
channelized streams. Over time, the channel is encroached on by plants,
which lay down sediments, which sucks up channel volume and makes people
think the ditches aren't "working" as a ditch should. As this encroachment
develops, I've noticed the channel takes on aquatic ecosystem
characteristics, rather than a culvert that's just lined with hard clay.
However, the standing agricultural logic is that the device is no longer
"working" and the ecosystem component goes away as soon as the ditch is
"cleaned". It comes back over time, as similar processes commence the
minute the backhoe is out of the channel, but the disturbance sends
literally tons of sediment downstream, and removes any potential
filtering/buffering capacity the encroached land and plants may have.
I am looking to the fish community as a response variable to encroachment
within the channel, or what I'm really after, how well the manufactured
system is behaving like a less disturbed system.
We've figured out a simple way to quantify the habitat as either
heterogeneous or homogenous. Now we're trying to determine if a significant
relationship in this habitat corresponds to the various types of habitat.
As Dave mentioned, biotic "diversity" is strongly correlated with habitat
diversity (heterogenity) is a topic agreed on by most ecologists. It's just
been troublesome to find a statistical metric to explain something as simple
as:
Habitat Type 1: 6/152, 9/144, 7/102 (species/individuals)
Habitat Type 2: 4/10, 4/48, 3/29 (species/individuals)
These are all tolerant species. These are all compromised systems. The
perspective is from a human standpoint, and one that hopefully acts like a
grade card on the reach of our ag activity in this area. More stable,
robust fish community, less impact off the fields. We're trying to find a
statistic to dimension words like "stable" and "robust".
Application in the real world? Well, I got paid to look at fish! :) But
more seriously, if it's just a matter of accounting for lost in-channel
volume to make a difference at the point of source that allows a fully
fledged vertebrate community to develop, and reduce downstream non-point
source ag pollution coming from first and second order "stream" sources...
We've got something to present to agencies that has some statistical bite,
and paired with some education and interpretation to farmers than "you've
got better bug community in your ditch".
So it's not really a "condition"... It's more like "what is which/what" and
"what does that tell us".
Might be nothing, if I can't figure this out :) And it will probably be a
solution that only works in the Glacial Lake Maumee basin. At least,
that'll cap the potential universe I have to fight with.
Todd
----- Original Message -----
From: <dlmcneely at lunet.edu>
To: <nanfa-l at nanfa.org>
Sent: Thursday, September 29, 2005 4:41 PM
Subject: Re: NANFA-L-- Diversity Indicies
> Irate, I did not identify the "condition," partly because Todd did not
> do so, and in fact, it was somewhat presumptuous of me to suggest he
> might be interested in something other than diversity, since that's
> what he asked about.
>
> Yes, diversity is beyond richness, and includes a component called
> evenness. Evenness refers to the degree to which the individuals in a
> sample are distributed across the species present. If a sample
> contains the same number of each of the species included, that sample
> has maximum evenness compared to samples with varying numbers of each
> species. The idea is that a sample with, say 996 of one species and 1
> each of each of another 4 species is almost the same as one that has
> simply 1000 of one species, whereas a sample that has 200 of each of
> five species is quite different from the unispecific sample of 1000.
>
> Now, does all this mean anything, or is it just an exercise?
>
> Some ecologists have attempted to use the concept of diversity to
> consider why some systems might be more resistant to degradation, or
> more resilient to degradation, or more capable of surviving
> degradation, or related matters, than other systems. Others have used
> diversity as a stand-in for state of degradation, almost as, well, an
> index, usually presumed to be inverse to degradation. But of course,
> very simple systems may not be degraded, as I mentioned in my earlier
> post. One thing that a fair number of ecologists have agreed on is
> that biotic diversity is strongly correlated with habitat diversity in
> undegraded systems, and that agreement is the result of a good many
> data sets. A classic early paper (1970s) in this field showed that the
> increase in species diversity with stream order is a correlate of
> habitat complexity. That was actually a starting point for James Karr,
> one of the co-authors of that work, to develop the IBI.
>
> Some other ecologists, like Hurlbert as mentioned by Bruce, have
> questioned whether "diversity" has any meaning whatsoever. Some have
> simply advocated using richness alone when one is interested in these
> sorts of things.
>
> There are lengthy discussions of these matters in ecology texts these
> days, and a whole series of competing mathematical ways of calculating
> diversity based on the number and distribution of species in a sample.
> The effort in developing such devices seemed to peak in the sixties of
> the last century, and application of them may have peaked soon after
> that. But maybe engaging in such matters is why we get so little done,
> and the natural world is falling apart while we dither? If you are
> interested further, consult any of the excellent laboratory manuals for
> a graduate level general ecology course (actually they are introduced
> in undergraduate courses for that matter) like Southwood, or Krebs.
>
> At any rate, literally thousands of reports have included diversity
> indices as a part of their data set.
>
> Dave
>
> David L. McNeely, Ph.D., Professor of Biology
> Langston University; P.O. Box 1500
> Langston, OK 73050; email: dlmcneely at lunet.edu
> telephone: (405) 466-6025; fax: 405) 466-3307
> home page http://www.lunet.edu/mcneely/index.htm
>
> "Where are we going?" "I don't know, are we there yet?"
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