Ecoregion Description

168: Ameca - Manantlan

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:

This ecoregion encompasses a small part of southern Nayarit, southern Jalisco, northwestern Michoacán, and the entire state of Colima. Its extent is determined by the watersheds of the Río Ameca in the north and the Río Ahuijallo in the south.

Drainages flowing into:

Drainages flow into the Pacific Ocean.

Main rivers or other water bodies:

There are several minor basins from the Río Ameca in the north to the Río Ahuijallo in the south, with each an independent basin draining into the Pacific Ocean.

Topography:

The ecoregion is mountainous, and traversed by numerous canyons. Elevations range from sea level to nearly 4000 m.

Climate:

The mean annual temperature of the ecoregion is 22 °C. The annual precipitation ranges between 630–1880 mm, with a mean of 1100 mm. In Colima, most of the rainfall occurs between August and September.

Freshwater habitats:

Freshwater habitats are characterized by coastal or short course rivers, with narrow or non-existent floodplains, especially in the northern areas.

Terrestrial Habitats:

Terrestrial habitats include primarily dry forests and pine-oak forests, with stands of mangroves along the coast.

Fish Fauna:

This ecoregion represents a transition between the Río Santiago [164] in the north and Río Balsas [169] in the south. The Río Ameca, the northernmost basin within the ecoregion, and the Armerìa, the southernmost basin, each have their own endemics, and share some species with the Santiago [164] or Balsas [169] ecoregions, respectively. However, they and the basins in between contain a shared fauna that slowly changes from north to south. For example, the range of the blackfin goodea (Goodea atripinnis) stretches north to the Río Santiago [164] ecoregion, whereas the ranges of the banded allotoca (Allotoca goslinei), blackspot allotoca (A. maculata), and Cichlasoma istlanum extend south to the Río Balsas [169] ecoregion.

Species of Allodontichthys, Ilyodon, Poecilia, Poeciliopsis and Xenotoca are common in the waters of Río Coahuayana and Río Armeria, and the leopard splitfin (Xenotaenia resolanae) is located in Río Ayuquila, Río Armeria, and Sierra de Manantlán.

Description of endemic fishes:

The Ameca-Manantlán is distinctive because of its endemism, especially among fish. Over half of its fish are endemic, and it has one endemic species of aquatic herpetofauna. Endemics usually occupy only one of the small basins within the ecoregion, except for Poeciliopsis, which is known to extend throughout the ecoregion in highly saline waters. There are a large number of endemic splitfins (Goodidae), including whitepatched splitfin (Allodontichthys hubbsi), finescale splitfin (A. polylepis), tuxspan splitfin (A. tamazulae), bandfin splitfin (A. zonistius), butterfly splitfin (Ameca splendens), goldbreast splitfin (Ilyodon furcidens), Limones splitfin (Ilyodon xantusi), golden skiffia (Skiffia francesae), leopard splitfin (Xenotaenia resolanae), black splitfin (Xenotoca melanosoma), and Tequila splitfin (Zoogoneticus tequilae). Some endemics in the Poeciliidae family include dwarf molly (Poecilia chica), golden livebearer (Poeciliopsis baenschi), and blackspotted livebearer (P. turneri). An endemic minnow, Algansea aphanea, is also found in the ríos Coahuayana and Armerìa.

Evolutionary phenomena:

The ecoregion is noted for speciation in the poeciliid genus Poeciliopsis and the goodeid Allodontichthys, and to a lesser extent in the genus Ilyodon.

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 represents a transition between the Río Santiago [164] to the north and Río Balsas [169] to the south. It also harbors a number of endemics.

Level of taxonomic exploration:

Poor, until recently. Explorations are continuing in the ecoregion.

References/sources:

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

Lyons, J., Gonzalez-Hernandez, G., et al. (1998). "Decline of freshwater fishes and fisheries in selected drainages of west-central Mexico" Fisheries 23(4) 10-18.