Ecoregion Description

166: Llanos El Salado

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

Salvador Contreras Balderas, Universidad Autónoma de Nuevo León. Additional text was modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment

Countries:

Mexico

Boundaries:

This interior ecoregion lies in central Mexico, primarily in San Luis Potosí, as well as Zacatecas, Nuevo León, Tamaulipas, and Guanajuato.

Drainages flowing into:

The Llanos el Salado is an endorheic basin—streams flowing into the basin have no outlet to the ocean. Instead, the water is lost primarily through evaporation. This type of drainage is fairly common throughout very arid, mountainous regions of the world.      

Main rivers or other water bodies:

The ecoregion contains only a few springs and short spring runs.

Topography:

Llanos el Salado lies on the Mexican Plateau and is mostly flat to hilly, with few mountains except along the ecoregion boundary. Elevations range from 400 to over 3400 m, grading down toward the Rio Grande/Río Bravo in the northeast and the Río Pánuco in the southeast. There is less drainage toward the Río Lerma in the southwest.

Climate:

The ecoregion experiences a semiarid climate. Mean annual temperature ranges between 11 and 23 ºC. Mean annual precipitation varies between 200 and 960 mm within the ecoregion, but averages around 425 mm.

Freshwater habitats:

There are primarily isolated springs, with no permanent runs. The basins are mostly arheic, with no signs of surface flows.

Terrestrial Habitats:

The terrestrial habitats are primarily comprised of dry scrub of the Meseta Central matorral and Central Mexican matorral, with pockets of Sierra Madre Oriental pine-oak forests.

Fish Fauna:

The ecoregion contains only a handful of species, including the Catarina pupfish (Megupsilon aporus) and members of the genus Cyprinodon in the Cyprinodontidae family and the relict splitfin (Xenoophorus captivus) and jeweled splitfin (Xenotoca variata) in the Goodidae family.

Description of endemic fishes:

The harshness of the habitats, the tectonism of the rock upon which these basins often sit, and the relative genetic isolation of the aquatic species of the basins has lead to the development of a highly specialized and unique fauna. The Llanos el Salado’s species richness is fairly low, but its endemism is high. Seventy-five percent of the fish species that are found in the area are endemic. These are restricted to members of theCyprinodontidae family, and include the Potosi pupfish (Cyprinodon alvarezi), Villa Lopez pupfish (C. ceciliae), Charco Azul pupfish (C. inmemoriam), La Palma pupfish (C. longidorsalis), Charco Palma pupfish (C. veronicae), and Catarina pupfish.

Other noteworthy aquatic biotic elements:

There is one endemic crayfish, Procambarus sp. 

Evolutionary phenomena:

The genus Cyprinodon represents an endemic monophyletic lineage with microgeographic speciation in a set of close springs within the single Sandia pluvial lake. These are closely related to the species in Potosí. Endemic genera are known from Potosí spring and the Venado-Moctezuma, Illescas, and Santa Maria group of springs. The fish fauna is highly relict, related to three different basins: Rio Grande for Cyprinodon, Pànuco for Xenoophorus, and Lerma for Zoogoneticus.

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. This ecoregion has high endemism in a highly fragmented environment, composed mainly of small springs or groups of springs.

Level of taxonomic exploration:

Good

References/sources:

Abell, R. A., Olson, D. M., et al. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.

Lozano-Vilano, M. L.,Contreras-Balderas, S. (1993). "Four new species of Cyprinodon from Southern Nuevo León, México, with a key to the C. eximius complex (Teleostei: Cyprinodontidae)" Ichthyol. Explor. Freshwaters 4 295-308.

Miller, R. R. (1976). "Four new pupfishes of the genus Cyprinodon from México, with a key to the C. eximius complex" Bull. So. Calif. Acad. Sci. 75 68-75.