Dear Mathieu,
Thanks a lot for your answer!!! I did something similar like you
suggested: I subsampled my data and tested if there still is a relation:
1) First I subsampled each month for each animal.
2) I took the animal with the lowest number of fixes. For each other
animal I randomly chose as many fixes as the animal with the lowest
number had.
I repeated that 20 times.
3) Then I calculated the UD for each of subsampled data.
4) I compared the UD results of those random chosen fixes to the one of
the original data which used many fixes. I used linear regression to
compare the results.
5) Still there a relation
So I do have a problem because there is a relation of the number of
fixes and the UD size. Are there any other ideas than subsampling by
hourly data?
Help would be very much appreciated!
Dagmar
Am 27.08.2017 um 15:07 schrieb Mathieu Basille:
Hey Dagmar,
What do you mean by "testing if the UD size is related to the number of
fixes"? Did you model UD size as a function of number of fixes using all
fixes for all animals? If that's what you did, you could also check if
it's
true by animal too. One way to do it would be to compute UDs for each
animal over samples of fixes for instance every 10, 20, 30, 40, 50 and 60
minutes, and see if there is any relation here. If there is, you may not
have other option than subsampling at the hour scale to compare all
animals
(but what does the UD mean if there is such variation related to
sampling?
I'm not familiar enough with BRBs to comment here). If there is no
relationship per animal, then you simply have animals with high number of
fixes AND large UDs!
Hope this helps,
Mathieu.
On 08/23/2017 03:59 PM, Dagmar wrote:
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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AniMov mailing list
[email protected]
https://lists.faunalia.it/cgi-bin/mailman/listinfo/animov
Am 27.08.2017 um 15:07 schrieb Mathieu Basille:
Hey Dagmar,
What do you mean by "testing if the UD size is related to the number of
fixes"? Did you model UD size as a function of number of fixes using all
fixes for all animals? If that's what you did, you could also check if it's
true by animal too. One way to do it would be to compute UDs for each
animal over samples of fixes for instance every 10, 20, 30, 40, 50 and 60
minutes, and see if there is any relation here. If there is, you may not
have other option than subsampling at the hour scale to compare all animals
(but what does the UD mean if there is such variation related to sampling?
I'm not familiar enough with BRBs to comment here). If there is no
relationship per animal, then you simply have animals with high number of
fixes AND large UDs!
Hope this helps,
Mathieu.
On 08/23/2017 03:59 PM, Dagmar wrote:
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!!!
_______________________________________________
AniMov mailing list
[email protected]
https://lists.faunalia.it/cgi-bin/mailman/listinfo/animov
_______________________________________________
AniMov mailing list
[email protected]
https://lists.faunalia.it/cgi-bin/mailman/listinfo/animov
