[R-sig-eco] Detecting outlier sample sites

[Keith Larson]

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I have binomial frequency data for an allele associated with
populations living in mountainous. These mountains run north to south
where sites are nearly fixed for this allele and lowland sites to the
east that lack the allele. At the south end of the mountains is a
hybrid zone. Despite the mountains continuing south through the hybrid
zone, the allele frequency shifts from nearly fixed to nearly absent.
This suggests that despite the assumed benefit for this trait in the
mountains, that there is a barrier for it in the hybrid zone
preventing its spread south in the mountains.

I have used a simple glm approach in R to identify that altitude is a
significant predictor of the allele frequency north of the hybrid
zone. If I include hybrid zone sites in the model, altitude is less
significant. If I add a hybrid zone dummy variable to the model and it
is also significant. I would like to find a statistical approach to
identify these "outlier" mountain sites in the hybrid zone both
statistically and graphically.

*******************************************************************************************
Keith Larson, PhD Student
Evolutionary Ecology, Lund University
Sölvegatan 37
223 62 Lund Sweden
Phone: +46 (0)46 2229014 Mobile: +46 (0)73 0465016 Fax: +46 (0)46 2224716
Skype: sternacaspia FB: keith.w.larson at gmail.com