Simpson's Diversity Index and Single Individuals

[ac2012]

Hello,

I'm trying to calculate the Simpson's Diversity Index (D), which I then convert to the reciprocal (1-D). I'm using the method described in "Measuring Biological Diversity" by Anne Magurran.

The problem is that many of my samples have only one individual of each species present in them.
I've noticed that when this is the case, no matter how many species are present 1-D = 1, which seems to suggest that diversity is at the maximum level possible.

In the spreadsheet I've put a link to below I've calculated an example containing 7 species and an example containing just 2 species.

It seems strange that the resulting 1-D should be the same for both of these.

I was wondering whether I should accept this as correct, and record 1-D as 1 for both of these cases, regardless of how strange it seems.

If anyone could let me know what is normally done in this situation I'd be very grateful.

Thank you very much.

https://www.dropbox.com/s/uivowprjfym1gjz/simpsons.png

[ac2012]

Sorry, that should have been the "complement" not the reciprocal. (1-D)