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Started by Mark Andersen
Thu, 06 Aug 1992 19:35
Geostatistics and the desert tortoise.
Author: Mark Andersen
Date: Thu, 06 Aug 1992 19:35
Date: Thu, 06 Aug 1992 19:35
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I have been asked to help analyze some data being collected on desert tortoises. Among other things, a goal of the study is to estimate the number of tortoises living in a 70 sq. mi. area in the Mohave desert here in southern California. Data are being collected on the number of "tortoise signs" (i.e., tracks and feces) in fixed triangular transects (four per square mile); these data will be converted to numbers of tortoises using standard conversions. My idea was to fit an interpolated surface of tortoise population density (via kriging), then integrate this surface over the study area to obtain an estimate of tortoise numbers. Obviously, there's more to this than just what I've presented here, but this is the crux of my question. Is it considered OK to use the integral of an interpolated surface as an estimate of population size in a study region in this way (seems reasonable to me)? Does anyone know of experiences that others have had in using this sort of procedure to estimate wildlife populations? Right now, I reading books on spatial statistics by Ripley, Haining, Cressie, Cliff&Ord, and Upton&Fingleton. Is there some other essential reference that I need? Thanks in advance for any and all help. Does Noel Cressie read this list? A former Masters' student of his (Mark Bryan) is a good friend of mine. Mark Andersen manderse@orion.oac.uci.edu Dept. of Ecology and Evolutionary Biology
Re: Geostatistics and the desert tortoise.
Author: Douglas M. Hawkins
Date: Thu, 06 Aug 1992 21:56
Date: Thu, 06 Aug 1992 21:56
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In article <2A817F03.29491@noiro.acs.uci.edu> manderse@orion.oac.uci.edu (Mark Andersen) writes:
>I have been asked to help analyze some data being collected on desert
>tortoises. Among other things, a goal of the study is to estimate the
>number of tortoises living in a 70 sq. mi. area in the Mohave desert
>here in southern California. Data are being collected on the number
>of "tortoise signs" (i.e., tracks and feces) in fixed triangular
>transects (four per square mile); these data will be converted to
>numbers of tortoises using standard conversions.
>My idea was to fit an interpolated surface of tortoise population
>density (via kriging), then integrate this surface over the study
>area to obtain an estimate of tortoise numbers. Obviously, there's
>more to this than just what I've presented here, but this is the
>crux of my question. Is it considered OK to use the integral of an
>interpolated surface as an estimate of population size in a study region
>in this way (seems reasonable to me)?
>
>Mark Andersen manderse@orion.oac.uci.edu
>Dept. of Ecology and Evolutionary Biology
This is a natural application for block kriging rather than the
point kriging you seem to have in mind. The attraction of
using block kriging directly rather than the approach you
outline is that you will be able to get a standard error
to go with your estimate of the total numbers. You will not
get this by using point kriging and integrating the result.
Doug Hawkins
------------
########## Douglas M Hawkins Dept of Applied Statistics
## ## ## University of Minnesota
###### ## ###### Voice (612) 625-8159 352 COB, 1994 Buford Ave
## ## ## ## ## Fax (612) 624-2719 St Paul
###### ## ## ## Internet: doug@umnstat.stat.umn.edu MN 55108-6042
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