Nonlinear Species Accumulation Curves

[daniel guertin]

Hello Folks,

I have river otter diet data obtained from analyzing 33 fecal samples from 3
different study areas. I am trying to make species accumulation curves for
each area to show that I have a large enough sample size to detect
differences in prey species between areas.

For each study site, I have plotted the cumulative number of species found
per unit sample (for example: if sample 1 had 4 species the first point
would go at X=1, Y=4.  If sample 2 had 4 species but 3 were the same species
found in sample 1 and 1 species was new, the point would be plotted at X=2,
Y=5, and so on).  I can see graphically that there is a nonlinear
relationship.  Thus, to fit a curve to my data, I need use a nonlinear
exponential model.  I have to provide the starting values for the
exponential model based on my plots.

Now to my problem...I have only plotted the data once to examine the
relationship and fit a curve. I would like to select samples to add to the
curve in a random order (about 100 times,) calculate the species
accumulation for each randomization and average the resultant curves. This
is what I can't figure out how to do in the SPSS interface.

I hope that made some sense. Any help would be greatly appreciated.

Thanks so much,
Dan

[Maguin, Eugene]

Dan,

Unless you have the answers that you need, could you say more about these
'species accumulation curves'. I think I understand the issue. You wish to
show that type or the number and type of prey animals differs between the
three sites. Each scat sample yields a list of prey animals. For each site
you can make a prey profile by summing and plotting the number of times each
prey type is found.

That said, it seems that given the 11 samples from each site, you want make
100 draws of a sample selection order that you will then use to compute and
plot your curves. There is also a requirement that a specific sample not be
drawn twice in a given order.

Let's start there. Is the preceding paragraph correct?

Gene Maguin