A data set, along with a rough manuscript draft and the beginning of an analysis was handed off to me to finish up. The data is straight forward: Every year, for 12 years, 500 chicks were captured and marked on an island used by a nesting colonial waterbird. “Recaptures” were done using re-sightings of those chicks as adults (>1 year) in subsequent years.
The analysis the co-authors would like to do is the Pradel model ‘Survival and recruitment’ in MARK, along with estimating the derived lambdas (Chapter 13 in the MARK book). The main question being: How have the annual population dynamics of this colony changed on this particular island?
I’ve spent some time reading through the MARK book along with other papers that describe and/or use variations of the Pradel model. While I understand the basic concept, conceptually these is a lot going on for me. I want to make sure the analysis is appropriate and I understand the results. Forgive my ignorance, I’m still trying to wrap my head around all of this.
1) Is there an issue with all marked individuals being first year (juvenile) birds? I know Pradel models use reverse time of the full encounter history, but in the case of this data any zeros before the initial banding are true zeros.
2) We know there are differences in survival between juveniles and adults, but the Pradel model does not allow for such effects. Chapter 7.1 in the MARK book describes how to do this with the CJS model and I understand that. How will this influence the final results of the Pradel model?
3) Would creating a grouping variable based on each cohort make sense or be informative? Perhaps it would do something to address the above?
4) If I were to run the Pradel ‘survival and recruitment’ model on all the data, with full time (year) dependency, what would the resulting estimates tell me? In the MARK book “lambda from time-symmetric models is the realized growth rate of the age class from which the encounter histories were generated”. Does this mean growth rates (and recruitment rates) are only specific to juveniles in the population, and not the colony itself? This statement confuses me because juveniles do grow into adults as the study progresses. There is a good chance I am not interpreting correctly.
Any guidance and feedback is very much appreciated! Population modeling is somewhat new to me, and I’m learning as I go. Thank you.