[R-sig-eco] Standardizing data

[Peter Solymos]

Bruce,

Standardizing might not be the best way to go if you have low counts.
You can possibly assume that events follow a homogeneous Poisson
process and rate varies with night length (linear or quadratic) [Y|x ~
Poisson(phi); log(phi)=f(x)]. You can estimate corresponding
coefficients by glm(). I think controlling for night length
differences work even if you throw in other covariates as additive
effects on the log scale.

You can get sunrise /sunset times from maptools::sunriset, be careful
with timezones though.

Cheers,

Peter

--
Péter Sólymos, Dept Biol Sci, Univ Alberta, T6G 2E9, Canada AB
solymos at ualberta.ca, Ph 780.492.8534, http://psolymos.github.com
Alberta Biodiversity Monitoring Institute, http://www.abmi.ca
Boreal Avian Modelling Project, http://www.borealbirds.ca


On Wed, Jan 23, 2013 at 7:16 PM, Bruce Miller <batsncats at gmail.com> wrote:
> Hi all,
>
> Posting this query again as no one replied.
>
> I need to create a way to standardize bat sampling data in northern
> latitudes not only by the Activity Index standardized by sample time
> (unit effort) but by the constantly changing night length.
>
> This was easy in the tropics with a straight forward application of my
> Acoustic Activity Index (AI) [Miller, B. W. 2001. A method for
> determining relative activity of free flying bats using a new activity
> index for acoustic monitoring. Acta Chiropterologica. 3: 93-105].
>
> This uses the occurrence of each species by 1-minute time blocks and is
> then standardized by "Unit Effort"  which is the total sample time each
> night in hours. With a night length that was fairly standard with only a
> small ą of 1 hr or so for seasonal variation and very small
> night-to-night change this seem OK.
>
> However looking at data from here in the northern latitudes,I need
> something else in addition.   The night length not only changes rapidly
> night-to-night during the summer, but has a very wide ą.  So using only
> AI -occurrences per each 1-minute time interval standardized by sampling
> time previously used in the tropics may not reflect a realistic
> comparison measure up here in the north.
>
> So my question is how to incorporate the length of each night into the
> AI standardized by sample time?
> How best to integrate the night length since that is one of the key
> factors constraining bat activity?
>
> */R/* seems awesome for running repetitive calculations once one has the
> code line script.  So I am trying to see how to develop such a new
> standardized /R/ code for two data sets, one a DF with the simple AI
> values that have already been standardized by unit effort and another
> that includes the ever changing sunset-sunrise data.
>
> For working out GGplot temporal activity plots by minute for each night
> it took bit of hand holding by Hadley as R does not (or at lead did not)
> "do time well".  Not sure what can be done with standardizing the data
> with changing night lengths form one night to the.   The crossover
> midnight may not be an issue for this calculation since we just need a
> total night length in decimal hours.
>
> Moon phase and % illumination is yet another issue, but not relevant at
> the moment.:-)
>
> Any and all suggestions welcome and the bats will depend on it.
>
> Bruce
>
> --
> Bruce W. Miller, Ph.D.
> Conservation Ecologist
> Neotropical Bat Projects
>
>
> office details
> 11384 Alpine Road
> Stanwood, Mi. 49346
> Phone (231) 679-6059
>
>
>
>         [[alternative HTML version deleted]]
>
>
> _______________________________________________
> R-sig-ecology mailing list
> R-sig-ecology at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
>