[tlocoh-info] Seasonal differences

[Andy Lyons]

Hi Michelle,

That's a good question. Expressed slightly more generally, it seems 
you're dealing with a dataset that has long temporal gaps in it, and 
wondering how those gaps will affect the construction of hulls and 
subsequent isopleths. Presumably you want to avoid generating hulls that 
cover areas where the individual wasn't seen, especially areas between 
two clusters of locations recorded at two different time periods.

A few lengthy time gaps in a dataset shouldn't necessarily create 
spurious cross-overs in space use. You can of course analyze groups of 
points recorded at different seasons separately (e.g., rainy season year 
1, rainy season year 2). Alternatively, you can analyze all the rainy 
season locations across multiple years as one group. If time is excluded 
in nearest neighbor selection (let s=0), hulls will be constructed 
around each point and the closest points in space (regardless of which 
year they fall in). If you include time, the points within the same 
season will be favored as nearest neighbors, because the temporal 
difference between two points collected a year apart will probably swamp 
out the distance in space (although it depends on the value of s of 
course). This will give you hulls that are local in space and time. In 
either case, the adaptive method for nearest neighbor selection will 
reduce the number of points used in hull construction in areas where the 
point density is low (e.g., outlying areas).

Hope this helps. If you're getting results that don't look right, there 
might be another issue going on. Long time gaps, for example, can also 
create what appear to be outlying points merely because sampling was cut 
off before the individual had a chance to spend much time in the area.  
Good luck and let me know if you have any other questions.

Best,

Andy



On 5/1/2014 3:01 AM, Michelle Kastern wrote:
> Hello tLoCoH list,
>
> I have a very basic question that I am hoping one of you might be able 
> to help with. I would like to know the seasonal differences of the 
> home range distribution of the collared individuals in the study I am 
> working on. However, I do not know if running tLoCoH with the time 
> gaps is showing incorrectly areas where individuals spent long periods 
> of time (dark blue spots). Basically I want to show dry and wet season 
> over two years. Currently I have just split the data and ran the 
> script but I think the 6 month gaps are affecting the hulls. Have any 
> of you tried this or have suggestions on how best to deal with 
> seasonal differences.
>
> Any help will be much appreciated.
>
> Kind regards,
>
> Michelle
>
>
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-- 
*Andy Lyons, PhD*
Department of Environmental Science Policy and Management
137 Mulford Hall #3114
University of California at Berkeley
Berkeley, CA 94720-3114

Phone: +1-510-325-5860
ajlyons at berkeley.edu <mailto:ajlyons at berkeley.edu>

http://www.andylyons.org
http://tlocoh.r-forge.r-project.org
http://www.novamodeler.com

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