How should K be defined when using chopped transects from the same colony?

[Julia Braga Morais]

Hi all,

I've been using the pcount function (unmarked) to model detection and abundance of penguins. My data consists of transects from a single colony, but for analysis, I split these transects into smaller "sites" (i.e., spatial subsampling within the same colony). I’m unsure whether K (the upper bound on abundance) should be lowered to reflect the maximum counts observed within these smaller transects, or if it should remain high to reflect the maximum expected abundance at the colony level, since the transects are not independent colonies but spatial replicates.

Is K site-specific in this context, or should it reflect the total abundance possible within the larger unit (i.e., the colony)? Technically all penguins could be in one of the transects, as the transects are continuous and the penguins can move, but that is not very likely at all.

Thanks in advance for your insights!

Best, 

Julia

[Jeffrey Royle]

hi Julia,

 Generally K should be set high enough so that the MLEs don't change when you increase the value of K a little bit. So you have to check this by trial and error, and don't really need to think about it beyond that.  I would suggest using the default value in unmarked as a starter (I think that's 100 + max count but you can check that).  So run it with that default value and then add 10 or something to check that the MLEs are the same.

regards

andy

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