Rio San Juan (Mexico)
Salvador Contreras Balderas, Universidad Autónoma de Nuevo León. Additional text modified from Abell et al. (2000).
Major Habitat Type
Xeric freshwaters and endorheic (closed) basins
Drainages flowing into
The Río San Juan originates in the mountains of the Sierra Madre Oriental and the Altiplanicie Mexicana, and flows eastward onto the coastal plains of eastern Mexico, where it converges with the Rio Grande (Río Bravo) on the U.S.-Mexico border.
Main rivers to other water bodies
Main rivers in the ecoregion include the Río San Juan and Río Álamo, both which flow into the Rio Grande/Río Bravo.
Part of the Rio Grande complex, the Río San Juan stretches from southeastern Coahuila through central Nuevo León, and northwestern Tamaulipas to the Rio Grande (Río Bravo) River.
Headwaters of the Río San Juan originate in the Sierra Madre Oriental (mostly within Área Natural Protegida Cumbres de Monterrey). The topography throughout the lower course is hilly in the piedmont and grades to plains toward the confluence with the Río Grande/Río Bravo.
Freshwater habitats in the ecoregion include springs, mountain creeks, plains rivers, and a few lagoons. There are some semi-isolated springs (such as Apodaca, Mezquital, Infiernillo, Huasteca, and others that have dried out) with strictly Neotropical species. However, most headwaters are Nearctic, with only one or two Neotropical species.
The ecoregion includes the following terrestrial ecoregions: Sierra Madre Oriental pine-oak forests, Chihuahua desert, Tamaulipan mezquital, and Tamaulipan matorral.
Description of endemic fishes
Like many xeric regions, the Río San Juan exhibits high endemism among its freshwater fauna. The only strict endemic to the ecoregion is Membras vagrans, although the Mexican red shiner (Cyprinella rutila), Salinas chub (Gila modesta), and Monterrey platyfish (Xiphophorus couchianus) are near-endemic. There are no known endemics from the Río Álamo sub-basin, although there is one distinctive form of ghost shiner (Notropis buchanani), as well as the northernmost population of shortfin molly (Poecilia Mexicana).
Justification for delineation
Ecoregion delineations were based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government. The delineation of this ecoregion was based on several endemics, as well as a high presence Notropis species.
Level of taxonomic exploration
Excellent for southern tributaries, but poor for northern ones.
- Abell, R. A.,Olson, D. M.,Dinerstein, E.,Hurley, P. T.,Diggs, J. T.,Eichbaum, W.,Walters, S.,Wettengel, W.,Allnutt, T.,Loucks, C. J.;Hedao, P. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.
- Smith, M. L. and Miller, R. R. (1986). "The evolution of the Rio Grand Basin as inferred from its fish fauna" C. H. Hocutt and E. O. Wiley (Ed.) The zoogeography of North American freshwater fishes ( pp. 457-485 ) New York, New York, USA: Wiley.
- Contreras-Balderas, S. (1967). "Lista de Peces del estado de Nuevo León" Monterrey, México: Cuad. Inst. Invest. Cient., Universidad de Nuevo León.
- Miller, R. R. and Smith, M. L. (1986). "Origin and geography of the fishes of central Mexico" C. H. Hocutt and E. O. Wiley (Ed.) The zoogeography of North American freshwater fishes ( pp. 487-517 ) New York, New York, USA: Wiley.
- Meek, S. E. (1904). "The freshwater fishes of Mexico north of the Isthmus of Tehuantepec" Field Col. Mus. Publ., 93, Zool Ser 5 pp. 1-252.
- Mayden, R. L. (1989). "Phylogenetic studies of North American minnows, with emphasis on the genus Cyprinella (Teleostei: Cypriniformes)" Misc. Publ. Mus. Nat. Hist. Univ. Kansas 80 pp. 1-189.
- Köppen, W. (1936). "Das geographische System der Klimate" Köppen W. and R. Geiger (Ed.) Handbuch der. Klimatologie ( (Vol. 1, pp. 1–44 ) Berlin, Germany: Gebrüder Borntröger.
- Kottek, M., J. Grieser, C. Beck, et al. (2006). "World Map of the Köppen-Geiger climate classification updated" Meteorologische Zeitschrift 15 pp. 259-263.
- Hijmans, R. J., S. Cameron and Parra., J. (2004) \WorldClim, Version 1.4 (release 3). A square kilometer resolution database of global terrestrial surface climate\ "<"[http://www.worldclim.org]">" (16 July 2009)