Fit two different functions for two strata

[Dayron Lopez]

Hello everyone,

I have data for a bird species in a reserve where two main habitat types are found (these are the two strata) and I would like to ask if and how is it possible to fit two different functions for the two habitats.

Do I have to change something in the model definition properties or elesewhere? What?

For another bird species I didn't have this problem because the same function was performing well for both strata but in this case it isn't.

Thanks a lot for your attention

Dayron Lopez 

[Eric Rexstad]

Dayron

Yes, it is possible to fit separate detection functions to each of two geographic strata (habitats).  You can demonstrate to yourself using the "minke" data set in the Distance package.  The data are of a stratified survey with a northern and a southern stratum.

minke.trunc <- 1.5
# Create dataset for South 
minke.S <- minke[minke$Region.Label=="South", ]
# Fit df to south
minke.df.S.strat <- ds(minke.S, key="hr", adjustment=NULL, 
                       truncation=minke.trunc)
summary(minke.df.S.strat)
# Create dataset for South 
minke.N <- minke[minke$Region.Label=="North", ]
# Fit df to south
minke.df.N.strat <- ds(minke.N, key="hr", adjustment=NULL, 
                       truncation=minke.trunc)
summary(minke.df.N.strat)

To do the equivalent in Distance for Windows, watch the video and conduct the analysis described in our online training materials here:

https://workshops.distancesampling.org/online-course/syllabus/Chapter5/#stratification-exercise
Chapter
 5 Stratification, clusters and covariates
In
 this chapter we introduce more challenging designs and analyses. The study area may be subdivided into smaller regions (strata) and density/abundance estimated within each strata.
workshops.distancesampling.org

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of Dayron Lopez <dayroni...@gmail.com>
Sent: 29 October 2021 13:38
To: distance...@googlegroups.com <distance...@googlegroups.com>
Subject: [distance-sampling] Fit two different functions for two strata

 

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