species diversity gradient problem

[Mike Crisp]

Currently I am dealing with a similar problem to that of Peter Schuchart
(below).  I am trying to relate species richness and endemism of plants in
Australia to climatic variables, latitude, etc.  Our data are scored in 1
degree grid cells, and we too have a problem of sampling artifacts, eg the
deserts are not well explored.  If sampling were not an issue, regression
is an obvious method to use, but it is very sensistive to sampling
artifacts.  Moreover, Peter Schuchart indicates that his search effort is
directly related to the variable he is testing, ie depth.  Separating these
in his data will be a big problem, maybe impossible.

There is a well known inverse relationship between species richness and
latitude, and a large literature about this.  These folk must have had to
deal with sampling problems.  See, eg, Brown, J. H., and Lomolino, M. V.
(1998). 'Biogeography.' 2nd edn. (Sinauer Associates: Sunderland,
Massachusetts.), chapter 15, and references therein.

I too would be interested in how other Taxacomers have dealt with the
'search effort' problem.

Mike Crisp
____________________________________________________
Peter Schuchart wrote:

>dear collegues
>could anyone give me some hints on publications
>with studies comparable to my case decribed below?
>
>I have identified all marine hydroids down to 2400 m depth from
>a collection made in a defined region. I would now like to
>know how species diversity decreases with depth.
>
>However, there are two ways of analysing this, and I don't know
>which one is more appropriate.
>
>First, I can define equal depth intervals of 100 m and then
>count the species present in the individual intervals. But this will
>lead to unequal sample sizes (unequal search effort).
>
>The other solution is to define depth intervals which have
>the same number of samples taken. This will lead to rather unequal
>intervals.
>
>I assume, that species diversity is both dependent on
>search effort and area (= depth interval).
>
>Both approaches give a decreasing species number with depth,
>but the first method gives a much more dramatic result.
>
>Any idea?
>cheers,
>Peter

_____________________________________
Dr Michael D. Crisp
Reader in Plant Systematics
Division of Botany and Zoology
Australian National University
Canberra ACT 0200 Australia

Phone + 61(0)2 6249 2882
Fax   + 61(0)2 6249 5573
E-mail mike.crisp at anu.edu.au
http://online.anu.edu.au/BoZo/crisp.html
_____________________________________