Detection species interaction factor

questions concerning analysis/theory using program PRESENCE

Detection species interaction factor

Postby Karla_Garcia » Thu Aug 31, 2017 6:03 pm

Hello!
I'm using two-species multi season occupancy models to study species interaction with the psiBa/rBa parameterization. I have 33 sampling points, that have been surveyed 3 times within each season during year. I have built models testing different scenarios, evaluating within-season effects and an individual detection covariate.

I initially limited the analyses to patterns of detection because the site spacing was not distant enough to ensure spatial independence between survey units for species A. For this reason, parameters for occupancy probabilities (i.e. ΨA, ΨBA and ΨBa) were modelled independently. However, I'm not sure if it's right to build models testing different scenarios for psiBA and psiBa, given that for species B was ensure spatial independence between sampling points.

I built models that assumed that the detection probability of the subordinate species was influenced by the presence (pB≠rBa; pB≠rBA) or detection (rBa≠rBA) of the dominant species or was independent of the dominant species (pB = rBa = rBA). I also evaluate a set of models where, give than both species are present, the detection of the dominant species was influenced by the detection of the subordinate species (pA≠ rA) or independent (pA= rA). Preliminary results showed that the detection of the both species was independent of the detection of the other species (i.e., pA = rA, pB=rBa=rBA). However, I found no consistent interaction in the detection process at sites occupied by both species (δ = 0.29). I calculated the detection species interaction factor (δ) adapted from the formula for phi from Richmond et al (2010):

δ=(rA*rBA)/(rA*((rA*rBA)+((1-rA )*rBa))

It’s right? /Is there any other way of obtaining detection species interaction factor?

Thank you very much in advance for any comment!
Karla_Garcia
 
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Re: Detection species interaction factor

Postby jhines » Tue Sep 12, 2017 3:37 pm

Hi Karla,

The formula for delta looks correct.

What do you mean by "no consistent interaction in the detection process" with delta=.29? I assume that value came from a model where rBA not = rBa, although you said that the results indicated that pB=rBa=rBA. A delta value of 1.0 meaans no interaction. Values < 1.0 mean the detections of both species are fewer than expected than if detections were independent.

You can have PRESENCE estimate the species interaction factor (phi for occupancy, delta for detection) by using the "phi/delta" parameterization (top option button in the run dialog window).

Jim
jhines
 
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Re: Detection species interaction factor

Postby Karla_Garcia » Mon Sep 18, 2017 10:32 pm

Thanks Jim!
In fact, the results of the best model indicated independence between the probabilities of detection (pA = rA, pB=rBa=rBA), however, when estimating delta showed a value <1.0, suggesting that the detections of both species are less than expected than if detections were independent (i.e. avoidance). I don't know why this incongruity. I'll try the phi/delta parameterization option.
Karla_Garcia
 
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Joined: Wed Jan 22, 2014 5:28 am


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