Interpreting occupancy vs. use in multiple-season models
Carolina Jankowicz
Hi, how are you?
I have a question regarding the possible interpretations of occupancy/use probability in a multiple-season model.
I have been working with single-season models, and in most cases—due to ecological and design considerations—we have found it preferable to interpret the probability as use rather than occupancy, since it was not clear that the species would be present continuously at what we defined as a site throughout the entire season.
However, I find it difficult to extend this criterion to multiple-season models. At least in the explicit modeling framework, where colonization and extinction are estimated: can I refer to a site as being “used,” and then talk about it being colonized or going extinct? I understand that, in numerical terms, if one interprets the parameter as use and estimates colonization, this would represent the rate or probability that use increases from one season to another. But ecologically, does this make sense?
In the implicit model, this feels less problematic, as I understand that I would simply be interpreting different probabilities of use that a site may have across seasons.
When it comes to designing the sampling scheme—particularly the distance between sites—it felt easier to apply a criterion in the single-season case. Even with some uncertainty about how much the species might move over certain time intervals, I could still find a way to interpret things appropriately based on the criteria used. In this case, with the added confusion about what colonization and extinction would imply under a “use” interpretation, I find it more difficult to interpret things ecologically.
I would greatly appreciate your guidance on this matter,
Kind regards,
Carolina
Josh Twining
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Carolina Jankowicz
Hi Josh,
Thank you for your response. I am working in a study area where the species was not present at the beginning of the study and colonized the area over the course of the sampling period (a process that took several years). I have sampling sites distributed across this area, and I am interested in understanding how this process unfolded: when did the species appear at each site? Is it possible to identify a spatial pattern in its return (for example, appearing first from the south)? I am not sure whether I will be able to characterize any form of intensity (i.e., few initial records vs. a higher frequency of records at the same site over time). I do not yet have those details fully defined, but broadly speaking, my goal is to characterize this type of process.
So I do expect site states to change over years, and I am interested in that change (as well as in incorporating potential covariates, e.g., distance to other potential sources). Do you think it makes sense to use a multiple-season framework?
Returning to my initial question, given the variability in the species’ movement patterns, I am not sure whether I can define a site as a unit that is either occupied or not, and I also do not think that would be particularly useful. I believe that a “use” interpretation is more appropriate. However, this is where my concerns from the initial message come into play.
Thank you very much for your time,
Carolina
Quresh Latif
Biometrician
--Joshua P. Twining, PhD,Assistant Professor,126 Nash Hall,Oregon State University,Oregon,97331Mob: (607) 220 7547
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Marc Kery
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Subject: Re: [unmarked] Interpreting occupancy vs. use in multiple-season models