GEM (Geographically explicit Event Model) is a method for phylogenetic biogeography to infer both biogeographic events (vicariance, full copy sympatry, point sympatry, and founder event) and geographic ranges at the internal nodes of a tree, if you have the explicit geographic ranges of the terminals.
GEM is based on Hovenkamp's ideas [1, 2] on using explicit distribution ranges in biogeography, on Ronquist's DIVA [3] on using and scoring events, as well as in the implementation of the Spatial analysis of vicariance [4], on geographic data models and algorithm mechanics.
It provides further development of the ideas presented in [4], and supersedes my older program, VIP
GEM is implementated in two pilot programs available as Windows and Linux executables, as well in source code (available under BSD-2 license).
[1] Hovenkamp, P. 1997. Vicariance events, not areas, should be
used in biogeographical analysis. Cladistics 13: 67. DOI:
10.1111/j.1096-0031.1997.tb00241.x.
[2] Hovenkamp, P. 2001. A direct method for the analysis of
vicariance patterns. Cladistics 17: 260. DOI:
10.1006/clad.2001.0176.
[3] Ronquist, F. 1997. Dispersal-Vicariance Analysis: A new
approach to the quatification of historical biogeography. Systematic Biology
46: 195-203. DOI:
10.1093/sysbio/46.1.195.
[4] Arias, J.S., Szumik, C.A., Goloboff, P.A. 2011.
Spatial analysis of vicariance: A method for using direct geographical
information in historical biogeography. Cladistics 27: 617-628. DOI:
10.1111/j.1096-0031.2011.00353.x.