Ecoregion Description

163: Mayran - Viesca

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:

The Mayrán-Viesca ecoregion is located in north-central Mexico, and crosses the states of Chihuahua, Coahuila, Durango, Zacatecas, San Luis Potosí, and Nuevo León. It is bounded to the west by the Sierra Madre Occidental and to the east by the Sierra Madre Oriental.

Drainages flowing into:

This ecoregion is a large endorheic basin located in north-central Mexico. It includes closed basins that once formed part of the Rio Grande/Río Bravo complex during pluvial times.

Main rivers or other water bodies:

This ecoregion is composed of the following interior basins: Río Nazas-Laguna Mayrán, Río Aguanaval-Laguna Viesca, Laguna Tlahualilo, Parras, upper Río Mezquital, and Laguna de Santiaguillo.

Topography:

The topography of the ecoregion ranges from flat plains in the interior of the ecoregion to peaks reaching upwards of 3500 m in the Sierra Madre Occidental. Additionally, the Continental Divide borders the ecoregion in the southwest.

Climate:

This ecoregion experiences a predominantly arid and semi-arid climate, with a mean annual temperature of 18 ºC, and mean annual precipitation around 380 mm.

Freshwater habitats:

This ecoregion is characterized by closed-basin streams and spring environments, all associated with high levels of endemism. Unique and isolated environments encourage the development of highly specialized biota and speciation by extant species to fill ecological niches.

Terrestrial Habitats:

Most of the ecoregion occurs within the Chihuahuan desert, which is one of the most biologically diverse arid ecoregions in the world. The Sierra Madre Occidental pine-oak forests in the western part of the ecoregion are also exceptionally diverse, and are characterized by species such as Lumholtz\' pine or pino triste (Pinus lumholtzii). Pockets of Sierra Madre Oriental pine-oak forest also occur throughout the ecoregion. The southern portion of the ecoregion is characterized by Meseta Central matorral.

Fish Fauna:

The ecoregion’s freshwater biodiversity is characteristic of endorheic basins, with a relative paucity of species, but high endemism. Species here are likely derived from the Rio Grande drainage to the east. The fish of the area are similar to those of the Rio Grande, but have adapted to the different ecological pressures of an endorheic system.

Description of endemic fishes:

Endemics to the ecoregion include the Nazas sucker (Catostomus nebuliferus), bold characodon (Characodon audax), Tepehuan shiner (Cyprinella alvarezdelvillari), Gibbous shiner (C. garmani), Mezquital pupfish (Cyprinodon meeki), Nazas pupfish (C. nazas), Nazas chub (Gila conspersa), Durango shiner (Notropis aulidion), and Nazas shiner (N. nazas). The bold characodon, Mezquital pupfish, and Nazas shiner are restricted to the upper Rìo Mezquital. Other species, such as the Nazas pupfish and Gibbous shiner, are shared with the Parras basin. The stumptooth minnow (Stypodon signifier) and Parras pupfish (Cyprinodon latifasciatus) are restricted to the Parras basin.

Other noteworthy aquatic biotic elements:

One endemic crayfish and one endemic species of aquatic herpetofauna (the salamander, Pseudoeurycea galeanae) occur here.

Ecological phenomena:

This ecoregion includes fish fauna of the upper Rìo Mezquital above the canyons (composed of Rio Grande derived fishes [cyprinoids, catostomids, a pupfish, and one percid]) and the Parras basin. Species divergence has taken place due to the fragmentation and isolation of the basins, particularly in the Parras basin, and the derived upper Rìo Mezquital sections.

Evolutionary phenomena:

Some of the local populations of apparently shared taxa may constitute valid species, still undescribed. The ecoregion also has the endemic genus Stypodon.

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 includes a high number of endemic taxa, including one genus (Stypodon). The basins of this ecoregion formed a tributary to the former pluvial Rio Grande basin, where its fauna is considered derived.

Level of taxonomic exploration:

Rather complete, except in higher headwaters.

References/sources:

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

Contreras-Balderas, S., Lozano-Vilano, M. L., et al. (2005)"Historical changes in the Index of Biological Integrity for the Lower Río Nazas, Durango, México" In Hughes, R.;Rinne, J.N. (Ed.). Fish assemblages in large rivers. Chicago: University of Chicago Press.

Contreras-Balderas, S.,Lozano-Vilano, M. L. (1994). "Cyprinella alvarezdelvillari, a new cyprinid fish from Río Nazas of México, with a key to the lepida clade" Copeia 1994(4) 897-906.

Contreras-Balderas, S.,M, A. M. Maeda (1985). "Estado actual de la Ictiofauna nativa de la cuenca de Parras, Coah., México" Mem. VIII Cong. Nal. Zool. (Méx.) 1 59-67.

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.

Smith, M. L.,Miller, R. R. (1986)"The evolution of the Rio Grand Basin as inferred from its fish fauna" In Hocutt, C.H.;Wiley, E.O. (Ed.). The zoogeography of North American freshwater fishes. (pp. 457-485) New York, New York, USA: Wiley.