Hi,
I write a brief note from an e-mail exchange with Prof. Efford that some users might find useful. I found a new problem and I think it would be better to continue the debate on the Forum.
I originally wanted to compare lizard density across three islands using SECR model. Each island has a different detectors’ grid and there are no movements of individuals across grids. Among the possible solutions, Prof. Efford suggested me to enter each island as a separate session and enter the trap ID-files in three different files (the order needs to match the one in the capture file). To import the data the syntax is
island<-read.capthist('capturefile.txt', c('traps1.txt','traps2.txt','trap3.txt'), detector='proximity')
The island effect can be tested by simpy comparing the two models:
fit0 <- secr.fit(island, model = D~1, buffer = 25)
fit1 <- secr.fit(island, model = D~session, buffer = 25)
This worked perfectly and I hope other users might find it useful as I did.
Now, however, a have a new problem. The models above assumed g0~1 (the same g0 across islands). When trying to change this I have an error message
fit2 <- secr.fit(island, model = D~session, g0~t, buffer = 25)
no verify method for objects of class formula
Error in if (notOK) stop("'verify' found errors in 'mask' argument") :
argument is of length zero
The same happened with g0~session
I do not know how to impose a g0 variable over the sessions and the islands.
Any suggestion?
Thank you very much in advance
Giacomo