Ecoregion Description

164: Rio Santiago

Major Habitat Type:

tropical and subtropical coastal rivers

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 ecoregion lies on the Pacific coast and includes the Islas Marías. The ecoregion covers the states of Durango, Nayarit, Jalisco, Zacatecas, Aguascalientes, and Guanajuato.

Drainages flowing into:

Drainages of this ecoregion flow into the Pacific Ocean.

Main rivers or other water bodies:

The extent of this ecoregion is largely defined by the watersheds of the Río San Pedro, the Río Santiago, and their tributaries, including the Río Mezquital, Río Grande de Santiago, Río BolaZos, and Río Juchipila. Río Santiago drains Lake Chapala, part of the Lerma – Chapala ecoregion [165].

Topography:

The topography is defined primarily by deep canyons of the Sierra Madre Occidental as well as the Trans-Mexican Volcanic Belt in the east. Elevations range from sea level to over 3000 m.

Freshwater habitats:

Freshwater habitats include major rivers with sand and rocks. This region is distinguished in part by its subterranean ecology. Aguascalientes is a warm aquifer located in the Mexican state that bears its name. It harbors unique populations of aquatic invertebrates such as rotifers.

Terrestrial Habitats:

Terrestrial habitats include mangroves and dry forests along the coast, Sierra Madre Occidental pine-oak forests at higher elevations, and matorral and Bajío dry forests in the interior. Characteristic species of the Bajío dry forest include Bursera, Ipomoea, and Ceiba.

Fish Fauna:

The fish fauna of this ecoregion is impoversihed, although it is rich in the atherinopsid Chirostoma and the poeciliid Poeciliopsis, with species such as charal (C. jordani), largetooth silverside (C. arge), shortfin silverside (C. humboldtianum), Lerma livebearer (P. infans), Sinaloa livebearer (P. presidionis), blackstripe livebearer (P. prolifica), and chubby livebearer (P. viriosa). Some species, including the blackfin silverside (Atherinella crystalline), Pacific molly (Poecilia butleri), Sinaloa livebearer, blackstripe livebearer, chubby livebearer, green guapote (Cichlasoma beani), and mountain clingfish (Gobiesox fluviatilis), are shared between the Río Santiago and lower Río Mezquital.

Description of endemic fishes:

The Santiago ecoregion is located on the western slope of the Sierra Madre Occidental and harbors relatively few known endemic aquatic species. Strict endemics to the ecoregion include the remote chub (Algansea avia), mountain chub (Algansea monticola), and Chapala catfish (Ictalurus ochoterenai). Some of the near-endemics include the spottail chub (A. tincella), Jalisco chub (Yuriria alta), yellow shiner (Notropis calientis), Lerma catfish (Ictalurus dugesii), largetooth silverside, shortfin silverside, olive skiffia (Skiffia lermae), spotted skiffia (Skiffia multipunctata), Lerma livebearer, blackstripe livebearer, and chubby livebearer.

Evolutionary phenomena:

Some species of the all-female Poeciliopsis genus are present in the ecoregion.

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.  In this ecoregion there was a high number of near- endemics, especially in Rìo Santiago.

Level of taxonomic exploration:

Relatively poor, due to inaccessibility.

References/sources:

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

Barbour, C. D. (1973). "The systematics and evolution of the genus Chirostoma Swainson (Pises: Atherinidae)" Tulane Stud. Zool. Bot. 18 97-41.

Contreras-Balderas, A. J.,Contreras-Balderas, S. (1988). "Los peces de Aguascalientes" México: Publ. Biol.. U. A. N. L..

Crossin, R. S., Soule, O. H., et al. (1973). "Biotic relationships in the Canon del Rio Mezquital, Durango, México" Southwest. Nat. 18(2) 187-200.