This is less an R question and more a request to the community for
literature references and the like.

I'm interested in the following inferential question.  What's the max
likelihood estimate for a path of travel of a point across a plane
having stable, smooth densities of two separate variables given two time
series of their values at the point as it moves?   Suppose all that's
available is the ratio of the variables?  

This is motivated by problems of inferring movement of biological
specimens between nesting and migratory regions, or the problem of
recovery of travel given the technique described here:

    http://www.pnas.org/cgi/content/abstract/105/8/2788

Despite that, are there R packages which might help this?  I ask because
I often find real gems buried within many R packages, gems which aren't
obviously related to their primary subject.

Thanks much.

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