Biotic Communities

Flowery rhetoric often gives birth to new terms that convey images and concepts, lead to inspiration and initiative. On the 1892-1894 expedition to resurvey the United States-Mexico boundary, Lieutenant David Dubose Gaillard described the Arizona-Sonora borderlands as “bare, jagged mountains rising out of the plains like islands from the sea” (Mearns 1907; Hunt and Anderson 2002). Later Galliard was the lead engineer on the Panama Canal construction project.

The Monte Desert of Argentina and the Sonoran Desert of North America are very similar in most aspects of their physical environments. The origins and the degree of affinity of thefaunas of three classes of vertebrates in the two deserts are discussed. Heterotherms show high endemism, with 72 0 % of the Monte species either endemic to the Monte or with Monte-Chaco distribution and with 61-4% of the Sonoran Desert heterotherms endemic to deserts of the southwest. Mammals show low endemism and theirdesertinhabitantsgenerallybelongto wide-ranging species.

An ecologically based classification system, when accompanied by digitized maps of biotic communities, has been shown to be useful for plotting and assessing affinities of plants and animals in the southwestern United States and northwestern Mexico. Because these maps show ecological relationships of plants and animals with their environment, maps of biotic communities can be especially informative when delineating and describing affinities of habitats.