Figure 4. Effect of prairie dog presence/absence on maintenance of the grassland ecosystem.

A) Prairie dog colony in Janos, Chihuahua, Mexico, note the absence of woody plants. B) Prairie dog expansion into ephedra shrubland by physically damaging the invading shrubs. Visible in the picture is the extensive browsing of shrubs, and several burrows at the base of the shrub which exposes the roots (see also map in Fig. 2D). C) Polygon of the southern portion of the prairie dog colony of Los Ratones, which was covered by grassland in 1988, showing a 43% advance of honey mesquite (Prosopis grandulosa) and ephedra (Ephedra trifurca) shrubland after the colony was poisoned between 1988 and 1990. D) Sixteen percent expansion of the La Báscula prairie dog colony into ephedra shrubland between 2000 and 2005.