To my fellow occupancy analysts,
I'm trying to aproximate the co-occurrence of two species using MacKenzie's 2-species model, and am interested in assessing to what extent (if any) the species are in competition with one another. I'm specifically interested in looking at the influence of biotic interactions on co-occurrence. Therefore, I included covariates in my models to assess the importance of difference biotic interactions (abundance of competitors, abundance of predators, etc). However, I'd also like to be able to directly assess whether there is competition is occurring between the two species for whom I'm modeling co-occurrence.
I'm well aware that the parameter, φ , provides you with some of idea of whether the occurrence of both species is purely random or not. However, this parameter is obviously not a direct measure of competition. To directly infer that competition was actually occurring, I've included a binary covariate indicating sites where both species were present and then observed whether any of my best models contained this covariate. My concern, is that there is a limited number (roughly 20%) of sites where the species do co-occur. Therefore, my expectation is that this covariate will falsely describe much more of the variance than it normally would assuming there were more sites where the species co-occurred. Any helpful suggestions on how I might get around this problem?
Thanks,
Josh