Do I need animal numbers detecte to calculate population density?

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xiangjun zhou

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May 2, 2022, 1:16:57 AMMay 2
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Hi, when calculating the population  density of animal, I did not import animal number detected, only  importing "Stratum , Area, Transect, Length,  Distance" . but I found that population density result were gived automatically, I want to know what is the reason? If that was not reasonable, I want to know when diatance analysis was finished,how to calculate population density and  population size, thank you!

Eric Rexstad

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May 2, 2022, 3:01:59 AMMay 2
to xiangjun zhou, distance-sampling
I don't know that I understand your question, but I have two suggestions.

If you want to know how the programme knows the number of detections, that is simply the number of distances you provide in the imported file.  Alternatively, if your question relates to animals that occur in groups (herds), then you should add an additional column to the file you import that records the number of animals in each detected group.

If neither of these answers address your question, please ask again.

From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of xiangjun zhou <zhouxia...@gmail.com>
Sent: 02 May 2022 06:16
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Hi, when calculating the population  density of animal, I did not import animal number detected, only  importing "Stratum , Area, Transect, Length,  Distance" . but I found that population density result were gived automatically, I want to know what is the reason? If that was not reasonable, I want to know when diatance analysis was finished,how to calculate population density and  population size, thank you!

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xiangjun zhou

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May 2, 2022, 8:36:19 AMMay 2
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Sorry, my english is not good, so may be  I expressed very bad. my question: when distance software finished all work, I found that estimated density have already given, but I don not import ant animal detected number, so the estimated density   represent   which density.  

xiangjun zhou

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May 2, 2022, 8:42:31 AMMay 2
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Snipaste_2022-05-02_20-33-46.jpg

Eric Rexstad

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May 2, 2022, 8:47:43 AMMay 2
to xiangjun zhou, distance-sampling
I apologise for not understanding your question.  Adding the output is helpful; I see you are using the bootstrap to estimate precision from the output you provided.  Do you want to know the units in which the density estimate is given?

On the page labelled "Density Estimates/Global", you will find the units of measure printed:

Is that helpful?

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xiangjun zhou

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May 2, 2022, 9:12:18 AMMay 2
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D represent estimated density, but I did not  provide any animal number detected, so I  don know  how "estimated density"  came from?  and  if not I have to calculate animal density with D= f(0)  N/2L,thank you

xiangjun zhou

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May 2, 2022, 9:19:05 AMMay 2
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sorry, I want to know why  "density" in that picture were created because I did not inport any anmimal  quantity which I detected in  Field investigation
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xiangjun zhou

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May 2, 2022, 11:24:14 AMMay 2
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It seem to be understand partly by me, do you mean: if I found many animals at same site in one transect line, I have to import them into distance software line by line or  separately ? thanks a lot.
在2022年5月2日星期一 UTC+8 15:01:59<Eric Rexstad> 写道:

Stephen Buckland

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May 2, 2022, 12:02:11 PMMay 2
to xiangjun zhou, distance-sampling

There are 2 cases.

 

  1. Animals occur singly.  In this case, you should have entered one distance for each animal, which allows the software to determine the number of animals detected.  If multiple animals were detected on a single transect, you will then have multiple rows in your data for that transect.  (You also need to include transects with no animals detected, so no distance recorded.)
  2. Animals occur in groups, and you record the distance of the group from the line, rather than of individual animals.  In this case, you will have an extra field for each detection, which is group size.  So for each distance recorded, you will have a field that tells the software how many animals were at that location.

 

Steve Buckland

xiangjun zhou

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May 2, 2022, 12:49:48 PMMay 2
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thanks a lot. I understand a lot. if single animal and groups all occur at the same time in certaintransecr line, how to deal with that? thanks a lot

Stephen Buckland

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May 2, 2022, 3:12:54 PMMay 2
to xiangjun zhou, distance-sampling

Treat as groups.  Single animals will have group size 1.

 

Steve

xiangjun zhou

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May 2, 2022, 11:17:12 PMMay 2
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thanks a lot, you are a good man ,wish you good day

Eric Rexstad

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May 4, 2022, 1:32:31 AMMay 4
to xiangjun zhou, distance-sampling
Perhaps you will need to show further input.  I presume you have entered or imported a file containing detections and effort (as you mentioned in an earlier email).  The software uses the data you provided to fit a detection function (providing the basis for the "f(0)" in the formula).  The number of detections constitutes the "n" in the formula and "L" in the formula is the total length of all replicate transects.


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xiangjun zhou

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May 4, 2022, 1:54:02 AMMay 4
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ok, I see. thanks a lot
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