Dear Magnus,

1. I think there is no diversity index that more appropriate for small 
species richness. If I'm wrong, someone will correct it.

2. You can calculate expected species richness for the same sample size 
(should be equal to or lower than the lowest sample size to avoid 
extrapolation) using rarefaction (see rarefy function in vegan package). 
In fact, it is equal to Hurlbert's diversity whose scaling parameter 
(m=2) is the sample size. Using low scaling parameter values (m>=2) may 
also be meaningful. Higher values of m makes the index more sensitive to 
rare species. For m=2 it is equal to the Simpson index. Advantage of 
Hurlbert-diversity is that it has unbiased estimator that consider the 
sample size (I'm not sure that it is used in rarefy function or not).

Best wishes

Zoltan

2013.02.19. 19:25 keltezéssel, Magnus Magnusson írta:
> Hi,
>
> I need help with a problem since I can't find an exact answer by
> reading/searching the internet.
>
> I have a dataset with 58 landscapes where  7 species in total may co-occur.
> However, some sites have different sampling efforts. I would like to
> calculate a diversity index value for each landscape so I can sort out
> landscapes with high diversity/poor diversity. The next step is to try to
> explain these diversity differences with e.g. degree of forest
> fragmentation in each landscape.
>
> So my question is:
> 1. Which diversity index would be most appropriate when having only 7
> species to consider?
> 2. How do I account for variable sampling effort in my count data when
> calculating a diversity index such as Simson's diversity index in the vegan
> package?
>
> /Magnus
> PhD-student in Umel', Sweden
>
> 	[[alternative HTML version deleted]]
>
>
>
> _______________________________________________
> R-sig-ecology mailing list
> R-sig-ecology@r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-ecology


-- 
Botta-Dukát Zoltán
--------------------------------
Ökológiai és Botanikai Intézet
Magyar Tudományos Akadémia
Ökológiai Kutatóközpont
--------------------------------
2163. Vácrátót, Alkotmány u. 2-4.
tel: +36 28 360122/157
fax: +36 28 360110
botta-dukat.zoltan@okologia.mta.hu
www.okologia.mta.hu


Zoltán BOTTA-Dukát
--------------------------------
Institute of Ecology and Botany
Hungarian Academy of Sciences
Centre for Ecological Research
--------------------------------
H-2163 Vácrátót, Alkomány u. 2-4.
HUNGARY
Phone: +36 28 360122/157
Fax..: +36 28 360110
botta-dukat.zoltan@okologia.mta.hu
www.okologia.mta.hu


	[[alternative HTML version deleted]]

