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Hi Julia,<br>
<br>
That's a good question, and probably very common as many GPS devices
are programmed to go to sleep during certain intervals to save
battery power. I don't think the omission of night time locations
would cause much of a problem in terms of generating a space use
model with T-LoCoH per say, but it would affect what you can claim
about your space use model (including the 'homerange' which is a
subset or product of a space use model).<br>
<br>
First thing to note is that when there is no sampling at night, the
estimated utilization distribution (isopleths) should be interpreted
as the UD of the sampled data, and not necessarily the individual as
a whole. Take for example a dataset where the sampling is once an
hour during the day, but the GPS unit goes to sleep from 6pm to 6am.
Now consider a nest, where the individual was recorded at 6pm, and
again at 6am, because it never moved during the night. If the goal
is to construct a utilization distribution that represents the
overall relative intensity of habitat use, then that nest should
really be represented by 13 locations, not 2. So we couldn't claim a
space-use model generated from those data represent that, but what
we can say more confidently is that the isopleths generated from our
data represent how space is used during the day, and that based on
our knowledge of the species, the overall pattern of space use will
be encompassed in the day time space use (although that may not be
true for all species). Whether or not that more conservative claim
about our analysis is an issue for the study as a whole depends on
the research question. If our research question only requires an
outline of the core area (50% isopleth), or the 'homerange' (95%
isopleth), and the gradient of use within the core or homerange
doesn't really matter, then this is probably not that big of a deal.
On the other hand if we're going to feed our UD into another level
of analysis where the gradient of the intensity of use matters, for
example a parameter estimation for a resource selection function or
volume intersection with another UD, then the omission of night time
points might be more of a deal breaker.<br>
<br>
Secondly, if you are generating time-use metrics (nsv and mnlv), you
certainly wouldn't want the intervisit gap period to be shorter than
the period the device was programmed to go to sleep, otherwise it
would appear as though a stationary individual (in the extreme case,
dead) was making multiple visits to the nest, when in fact it hadn't
moved at all. Does that make sense?<br>
<br>
If the omission of night time points is a deal-breaker for your
analysis, you could potentially model the missing data (i.e., insert
fake nightime points) based upon the assumption that the individual
didn't move during the night. T-LoCoH doesn't have a function to do
this, but it wouldn't be hard to make one. You could also test
whether the insertion of fake points is reasonable or not by
computing the distance between the last location of each day and the
first location of the following day, and see if indeed the distances
are actually close to zero.<br>
<br>
Hope this helps. I invite others to chime in, as these are issues
that affect not just T-LoCoH but any kind of space-use modeling
method.<br>
<br>
Andy<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 9/10/2014 10:13 AM, Julia Krejci
wrote:<br>
</div>
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<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB">Hi,
thank you for your quick answer!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB">I
have another question, not really related to the one below:
My transmitters were switched off during the night to save
energy and because the birds I investigate are only active
during the day. This creates a gap in the data, which is
also visible in the </span><span style="color:windowtext"
lang="EN-GB">lxy.plot.freq(my.lxy, deltat.by.date=T) </span><span
style="color:#1F497D" lang="EN-GB">function. I’ve attached
an example. Does this in any way affect the analysis? What I
want is basically home range and core area, nsv and mnlv. Do
I have to account for that in any way? <o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB">Thank
you,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB">Best
wishes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB">Julia
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-GB"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF
1.0pt;padding:3.0pt 0cm 0cm 0cm">
<p class="MsoNormal"><b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:DE-AT"
lang="EN-GB">Von:</span></b><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:DE-AT"
lang="EN-GB"> Andy Lyons [<a class="moz-txt-link-freetext" href="mailto:lyons.andy@gmail.com">mailto:lyons.andy@gmail.com</a>] <br>
<b>Gesendet:</b> Mittwoch, 10. September 2014 11:56<br>
<b>An:</b> Jul</span><span
style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;mso-fareast-language:DE-AT"
lang="DE">ia Krejci<br>
<b>Cc:</b> <a class="moz-txt-link-abbreviated" href="mailto:Tlocoh-info@lists.r-forge.r-project.org">Tlocoh-info@lists.r-forge.r-project.org</a><br>
<b>Betreff:</b> Re: [tlocoh-info] WG: nsv and mnlv<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Julia, <br>
<br>
Good questions. See some comments below. Also take note:<br>
<br>
1) Version 1.17 of the T-LoCoH package has a bug. If you
updated to that version, <b>please update to v1.18</b> (which
was posted today)<br>
<br>
<tt><span style="font-size:10.0pt">update.packages(oldPkgs="tlocoh",
repos=<a moz-do-not-send="true"
href="http://R-Forge.R-project.org">"http://R-Forge.R-project.org"</a>)</span></tt><br>
or<br>
<tt><span style="font-size:10.0pt">install.packages("tlocoh",
repos = <a moz-do-not-send="true"
href="http://R-Forge.R-project.org">"http://R-Forge.R-project.org"</a>)</span></tt><br>
<br>
2) There's a new tip sheet about time-use analysis on the
website that you might find useful, see <a
moz-do-not-send="true"
href="http://tlocoh.r-forge.r-project.org/tips_faqs.html">http://tlocoh.r-forge.r-project.org/tips_faqs.html</a>.<br>
<br>
Other comments below:<o:p></o:p></p>
<div>
<p class="MsoNormal">On 9/9/2014 6:33 AM, Julia Krejci wrote:<o:p></o:p></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<p class="MsoNormal"><span lang="EN-GB">Dear tlocoh-list,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">I’ve calculated
revisitation rate and mean duration of visit for some
birds I put GPS-transmitters on. I chose an
inter-visit-gap of 12 hours. Maybe I’m already work-blind,
but I can’t seem to understand the intervals the output
gives me. </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">If I display the nsv
data, it shows me all points which are considered as
consecutive visits to a hull, right? And the colour code
shows if the individual was there rarely or often. The
intervals of my output are:</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">1 – 11.6 </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">11.6 – 22.2 </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">22.2 – 32.8 … and so
on.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">So, this means, the
individual revisited this hull once or 22 times during one
inter-visit-gap? That doesn’t seem right. I’m quite sure
I’m missing something.</span><o:p></o:p></p>
</blockquote>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><br>
</span><span style="font-size:12.0pt;font-family:"Times
New
Roman","serif";color:blue;mso-fareast-language:DE-AT">nsv
stands for number of separate visits, where a visit is
defined as not being away from the hull for 12 hours or
more. So the hull where nsv=22 doesn't mean the individual
visited 22 times during one intervisit gap period, but
rather it was there and left for more than 12 hours and then
came back, 22 times.<br>
<br>
nsv values will of course be integer values. Those ranges
you show I presume are from the plot legend, which R
computes by taking the range of values and chopping it up
into equal intervals. But the nsv values themselves should
be all integers<br>
</span><span style="font-size:12.0pt;font-family:"Times
New
Roman","serif";mso-fareast-language:DE-AT"><br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"> It is the same for the
mean duration of visit. This means the mean number of
records taken of an individual during one visit to the hull,
right? But the output gives me</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">1.30 – 11.56</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">11.56 – 21.82 and so on
up to 52.60. </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">This cannot mean the
bird stayed in this hull for 52 records. My GPS interval is
one hour and the transmitters are shut down during the night
to save energy, so they don’t record over night. Maybe I
have to keep that in mind?</span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><br>
</span><span style="font-size:12.0pt;font-family:"Times
New
Roman","serif";color:blue;mso-fareast-language:DE-AT">A
hull where the mnlv=52 means the animal was within the hull
for 52 locations during at least one visit, where a visit
again is defined by a period of separation. Hence that "one
visit" could theoretically go on for several weeks, if for
example the individual left and returned every 11 hours like
clockwork, it would all be considered one visit because your
inter-visit period is 12 hours. That of course is very
unlikely, more probably the hull where mnlv=52 could also
contain a bunch of closely spaced locations, perhaps a site
where it stayed for a long time or returned at intervals
shorter than your ivg value, etc. The tip sheet on the
website illustrates how you can investigate the time use
metrics of individual hulls.<br>
</span><span style="font-size:12.0pt;font-family:"Times
New
Roman","serif";mso-fareast-language:DE-AT"><br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"> I tried to send you a
sample image for illustration</span><span
style="color:#1F497D" lang="EN-GB"> </span><span
lang="EN-GB">but it seems to be too big to be sent. </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">I hope my explanation is
understandable. I’d be very grateful for some advice.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">Thank you and best
wishes,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB">Julia </span><o:p></o:p></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><br>
H</span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";color:blue;mso-fareast-language:DE-AT">ope
this helps. Let me know what other questions you come across</span><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT">.<br>
<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><br>
<br>
<o:p></o:p></span></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>Tlocoh-info mailing list<o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="mailto:Tlocoh-info@lists.r-forge.r-project.org">Tlocoh-info@lists.r-forge.r-project.org</a><o:p></o:p></pre>
<pre><a moz-do-not-send="true" href="http://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/tlocoh-info">http://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/tlocoh-info</a><o:p></o:p></pre>
<p class="MsoNormal"><span
style="font-size:12.0pt;font-family:"Times New
Roman","serif";mso-fareast-language:DE-AT"><o:p> </o:p></span></p>
</div>
</blockquote>
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