CommunityCorrelogram (version 1.0)

lagSelect: Lag Selection

Description

Function lagSelect provides multiple community correlograms of varying lag sizes to assist in optimizing lag size and number.

Usage

lagSelect(sampleData,sampleLocation=NULL,sampleTime = NULL,LocationNames=NULL,
lagmin,lagmax,by,option=1,numTests=99,plot=T,anisotropic=F,...)

Arguments

sampleData

A matrix or dataframe with samples as rows and species or populations as columns

sampleLocation

A matrix or dataframe of xyz, xy (surface) plane and the z (depth) plane, geographical coordinates for objects in sampleData (used for spatial analyses only)

sampleTime

A numeric, date, or POSIX format vector of sample collection times for the objects in sampleData (used for temporal analyses only)

LocationNames

A character vector of location names for the objects in sampleData (used for temporal analyses grouped by location)

lagmin

Minimum lag size to compute in the units of distance (for options 1 and 3) or time (for options 2 and 4)

lagmax

Maximum lag size to compute in the units of distance (for options 1 and 3) or time (for options 2 and 4)

by

Number to increment tested lag sizes by

option

A switch specifying type of correlogram to be determined (spatial, temporal, or a combination of both). Options include: 1 = spatial analysis only (provide sampleLocation), 2 = temporal analysis only (provide sampleTime), 3 = spatial analysis grouped by sampling event (provide sampleLocation and sampleTime), 4 = temporal analysis grouped by sampling location (provide sampleTime and either sampleLocation or LocationNames). Default = 1.

numTests

Number of permutations used to calculate significance. Default = 99.

plot

A switch specifying whether to plot the community.correlogram calculated from each lag size. Default = T.

anisotropic

A switch specifying whether an anisotropic analysis should be performed. Default = F. The user is advised to consider whether an anisotropic analsysis is appropriate for their particular dataset and specify a value for anisotropic accordingly.

...

Other parameters passed to commcorrelogram

Value

Returns a list of objects of class community.correlogram, each with different lag size used to compute them.Plots of community correlogram metrics and significance values are created for each lag size tested when plot = T.

Details

Optimization of lag size is critical for geostatistical analyses (Goovaerts, 1997). This function provides correlograms over a range of lag distances within user specified minimum and maximum distances, calculated using commcorrelogram(). Some general rules of thumb exist for selection of lag size and number (Journel and Huijbregts, 1978; Legendre and Fortin, 1989):

1. The lag distance must be larger than the smallest sampling distance.

2. A minimum of 30 sample pairs per lag distance is recommended.

3. The maximum distance class should be no more than 2/3 the total sampling site distance.

It is helpful when using this function to use a small value for numTests, to improve speed and reduce computational intensity.

References

Goovaerts, P. 1997. Geostatistics for natural resources evaluation. Oxford, England: Oxford University Press.

Journel, A. G. and C. J. Huijbregts. 1978. Mining Geostatistics. San Diego, CA: Academic Press.

Legendre, P. and M. J. Fortin. 1989. Spatial Pattern and Ecological Analysis. Vegetatio 80(2): 107-138.

See Also

commcorrelogram

Examples

  ## Not run: 
#     #spatial lag selection
#       data(mite)
#       data(mite.xy)
#       lagSelect(sampleData=mite,sampleLocation=cbind(mite.xy,z=0),lagmin=0.1
#       ,lagmax=1,by=0.1,numTests=9)
#       
#       #temporal lag selection
#       data(pyrifos)
#       pyrifos.levels<-data.frame(ditch=gl(12,1,length=132),
#       dose=factor(rep(c(0.1, 0, 0, 0.9, 0, 44, 6, 0.1, 44, 0.9, 0, 6),11)),
#           week= as.numeric(as.character(gl(11, 12,
#           labels=c(-4, -1, 0.1, 1, 2, 4, 8, 12, 15, 19, 24)))))
#       lagSelect(sampleData=pyrifos,sampleTime=pyrifos.levels$week,
#       option=2,lagmin=1,lagmax=6,by=1,numTests=9)
#   ## End(Not run)