[R-sig-eco] Individual growth rate in a population with repeated sampling and overlapping cohorts

[GiulianoC]

Dear all,

I am trying to infer the average individual rate for two different
populations of iguanas. The two populations were established in 2002. Since
then I have samples from the first borns in 2002 and then 2003, 2004, 2005,
2007, and 2009. Every time we sampled we caught as many individuals as
possible. For the first 3 years of sampling it is fairly easy to assign
individuals to the right cohort. For the remnant years I am not 100%
positive to which cohort the newly captured individuals belong if they are
larger than expected at hatching time. 

At each capture I take standard morphological measures (SVL in mm, mass in
grams, head width and head length in mm). Since my samples sizes are not
huge (52 in one pop and 140 in the other) I was planning to retain all my
samples, even the recaptures over time.

So, I was thinking about applying a non-linear mixed model to infer a rate
of individual growth, but I am a little concerned about the overlapping
cohorts issue.

Any thought or suggestion is more than welcomed.
Also, please let me know if I need to expand on my problem.

Sincerely

Giuliano Colosimo
PhD Candidate in Conservation Genetics
Dept. Biological Science
Mississippi State University   



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