Dear all,
I want to compare the homerange size between animals based on GPS data
but it seems not to work.
Here is what I did:
I calculated the homeranges using the Biased random bridges from
adehabitat HR.
Animal_ltraj <- as.ltraj(animalxy, animaltime, id=TierID)
D_Animal <- BRB.D(Animal_ltraj, Tmax=21600, Lmin=36)
Animal_Grid <- ascgen(allanimals_xy, cellsize=32) # I chose 32 because
it was the smallest cellsize chosen automatically. I thought to compare
homerange size between animals I must use the same grid for all of them.
Animal_BRB <- BRB(Animal_ltraj, D=
D_Animal,type=c("UD"),Tmax=21600,Lmin=36, hmin=100,grid=Animalgrid)
kernel.area(Animal_BRB, unout=c("km2"))
My problem:
I have very different sample sizes (i.e. number of fixes): Most animals
were located hourly but two animals were located about each 5 min. This
results in sample sizes of about 150 fixes per animals and some animals
do have almost 10.000 fixes for the same periods of time.
Because I want to compare the resulting home range sizes I tested if the
UD size is related to the number of fixes and unfortunatly (!!) they are.
That means that I cannot compare homerange sizes between my animals
My question:
- did I do something wrong?
- is that problem known and is there a way to solve it?
The only way that I find is to reduce the number of fixes of my
frequently located animals artificially / randomly to start with the
equal number of fixes for all animals. This would be a shame though!
Help would be very, very, very much appreciated!!!
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