Hi all,

Just to give a proper background I will briefly explain what I am working on. I am running currently analysing the data from a project that aims to estimate lizard density on several sites, over a 5-month period. I have 14 sites (grouped in 3 main study areas), which I have visited twice per month (5 sessions, 2 occasions). Half of these sites correspond to capture locations within the area of an invasive predator, the other half are control sites. Within the invaded sites, I have an extremely low number of lizard captures. Therefore, to ensure model convergence I ran separate models for each area, indicating that each site was a separate session. To reduce computational burden, and work with 'closed' populations, I further subdivided data in sessions, so that I finally ran 3x5 models (for each study area and session combination). I ran all models maximizing conditional likelihood (CL=T) to save some time, and finally retrieved site-specific density using 'derived' function, and that's where my problem begins.

When I look at the estimates from derived function, I get some extremely odd results. Density looks like a really huge number (something like 9.402571e+15), whereas the esa is extremely small (3.349110e-08). At first glance, I thought this could mean that results are on the link scale and needed to be back-transformed. After that I started wondering if there could be any chance that the derived function changed the units (lizard/km^2, for instance). Another alternative (likely the most plausible) is that my model is wrong. After reading some papers I noticed secr models require a certain amount of recaptures to attain reliable results. I have 40-50 recaptures in the overall study, but after breaking up my dataset I am clearly below the safe minimum for secr models (10 recaptures per model). In spite of that, my CVD looks really good, with an average value of 9.02 for all models. Furthermore, when I run the models mximizing the full likelihood (CL=F) density estimates look much more decent (around 20 lizard/ha), although density in invaded sites is below zero, which is really weird. Right now I am struggling to understand whether the model is ok and I just missed something, or if should just migrate to non-spatial open-population models in openCR. Any feedback would be really helpful.

Thanks in advance!