Size ratio model is a data frame where each row is a different species and each column is a different site. In the size overlap analyses, each entry represents the body size of a particular species in a particular site. In phenology analyses, each entry represents the peak flowering time of a particular species in a particular site. EcoSimR comes with an example data set from Brown (1975).

Sizes of desert rodents
species Sonoran
Perognathus_flavus 7.2
Reithrodontomys_megalotis 11.4
Perognathus_penicillatus 17.1
Peromyscus_maniculatus 24.3
Dipodomys_merriami 45.3
Dipodomys_spectabilis 120.0

Using the defaults you can run a model with a uniform size algorithm and a variance ratio metric

rodentMod <- size_null_model(dataRodents)
summary(rodentMod)
## Time Stamp:  Tue Mar 31 22:24:01 2015 
## Reproducible:  FALSE 
## Number of Replications:  1000 
## Elapsed Time:  0.15 secs 
## Metric:  var_ratio 
## Algorithm:  size_uniform 
## Observed Index:  0.25135 
## Mean Of Simulated Index:  3.6846 
## Variance Of Simulated Index:  21.524 
## Lower 95% (1-tail):  0.31041 
## Upper 95% (1-tail):  13.572 
## Lower 95% (2-tail):  0.23314 
## Upper 95% (2-tail):  17.999 
## Lower-tail P =  0.032 
## Upper-tail P =  0.968 
## Observed metric > 32 simulated metrics 
## Observed metric < 968 simulated metrics 
## Observed metric = 0 simulated metrics 
## Standardized Effect Size (SES):  -0.74

Get a standard histogram plot of output.

plot(rodentMod, type="hist")

Plot observed vs simulated body size data.

plot(rodentMod, type="size")

References

Brown, J. H. 1975. Geographical ecology of desert rodents. Pages 314-341 in M. L. Cody and J. M. Diamond, eds. Ecology And Evolution Of Communities. Harvard University Press, Cambridge.