How does one measure a dynamic phenomenon with a static measure?
WT
----- Original Message -----
From: "Steve Brewer" <[email protected]>
To: <[email protected]>
Sent: Friday, January 30, 2009 6:04 AM
Subject: Re: [ECOLOG-L] Analysis of habitat specificity and circular logic
Brian,
I agree that the approach you described is circular and troublesome.
For what its worth, I recently published an article (Brewer and
Menzel, 2009. A method for evaluating outcomes of restoration when no
reference sites exist. Restoration Ecology 17:4-11) that might be of
some interest to you. It uses multivariate statistics to convert
presence/absence data of plant species in communities listed and
described in flora manuals for a given region to quantitative
habitat fidelity or indicator scores. These indicator scores can then
be used to calculate weighted averages of abundance or occurrence
within given localities to determine the extent to which the
community at a given site given contains species indicative of a
given habitat interest (e.g., mature forest, anthropogenically
disturbed communities, etc.).
One potential problem I've encountered in recommending this approach
to animal ecologists is that plant manuals tend to be more precise in
the description of the plant communities in which each species occurs
(e.g., calcareous hardwood forests, longleaf pine savannas, etc. as
opposed to "fields, "forests", "open areas"). At least that's what
I've been told by bird and arthropod biologists. This may be because
many animal species tend to cue in on structural characteristics of
the habitat as opposed to precise compositional characteristics.
Also, with birds (and some arthropods), you have the additional
complicating factor of migration.
Steve Brewer
At 4:18 PM -0500 1/29/09, Brian D. Campbell wrote:
Dear listserv members:
I've been reading a lot of literature recently on the effects of
fragmentation and land-use conversion from forests to agroforests and have
been really troubled by what seems a pervasive issue (at least in my
mind);
defining the biodiversity value of a human-modified habitat type (e.g.
either fragment or agroforest). Almost all studies I've reviewed
partition
bird communities into categories of "forest species", "rainforest
specialists", "agricultural generalists", among others, and proceed to
compare these among different land-uses. This is not my issue per se, but
rather, I find it very circular if one uses the data/observations they
collected in a study to define these groups; e.g. all species encountered
in
a "control" site of extensive forest were defined as forest species.
These
make useful and note-worthy observations but if one then proceed to
include
control sites in a statistical comparison then I think there is major
issue
with circularity. This also seems to me a very different approach than
having defined a priori (e.g. from distribution lists or other literature)
a
set of forest-candidate species which may or may not be present in any
given
site surveyed. Have others here found similar issues when reviewing papers
dealing with the biodiversity values of secondary forest and agricultural
habitats?
Brian Campbell
--
Department of Biology
PO Box 1848
University of Mississippi
University, Mississippi 38677-1848
Brewer web page - http://home.olemiss.edu/~jbrewer/
FAX - 662-915-5144
Phone - 662-915-1077
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