Boundaries

The ecoregion includes drainages along the eastern slopes of the Andes above 800 m that drain into the Amazon Basin. It extends from the Río Caguán in Columbia south to the Río Grande, a tributary of the Mamoré in Bolivia.

Topography

The topography of the Andes is complex and dramatic, punctuated by steep ranges that demarcate the western boundary of the Amazon Basin. Compared to the Guiana and Brazilian shields, the Andes are geologically young and tectonically active. The ecoregion includes much of the central and eastern slopes that extend from roughly the 800 m elevation contour to over 5000 m asl. Some peaks, like Nevado Ausangate in the Cordillera Vilcanota near Cusco, Peru, exceed 6000 m. Soils are composed of inceptisols, ultisols, mollisols, and exposed rock (at high elevations >4000 m asl).

Freshwater habitats

Most Andean streams are fast-flowing and are marked by rapids, waterfalls, gorges, and rocky beds. They are clear during the dry months and become turbid during heavy precipitation. There are also a number of alpine lakes filled with snowmelt. Glacial waters from Nevado Mismi flow into the Río Apurímac and are considered the headwaters of the Amazon. The four major Andean tributaries (with headwaters above 500 m) that intersect with the Amazon main stem are the Solimões, Iça (Putumayo), Japurá (Caquetá), and Madeira. Together their mean annual flow is 90,000 m³/s, which is roughly half of the Amazon’s mean annual discharge. Even though the Andes supplies less than 25% of the water volume to the Amazon, it supplies a disproportionate amount (more than 90%) of suspended sediments. Many high-altitude rivers have a pH greater than 7.0, with some as high as 8.75. They also tend to have high conductivity levels and high dissolved oxygen levels.

There are a number of Ramsar sites in the ecoregion, including Laguna de la Cocha; Ñucanchi Turupamba wetland complex; Complejo Llanganti, a complex of glacial lagoons; Lagunas Las Arreviatadas, a wetland complex with glacial lagoons; Reserva Nacional de Junín, a high-altitude freshwater lake; and Humedal Lucre – Huacarpay, a high-altitude wetland.

Terrestrial habitats

The Andes are considered to be one of the most diverse areas on earth. Terrestrial habitats in the ecoregion are roughly divided into submontane forest (700-2000 m), montane forest (2000-2500 m), cloud forest (2500-3500), and puna (3500-5000 m). The montane and cloud forests are very diverse and form a transition between the Amazonian lowland forests and puna.

Description of endemic fishes

There are 17 recorded endemic fish in five families. Of these, more than 70% occur in three genera: Orestias, Trichomycterus, and Astroblepus. The high Andean lakes and streams are home to a handful of endemic Orestine fish (O. gymnotus, O. jussiei, O. mundus, O. polonorum, and O. empyraeus) and a few endemic pencil (Trichomycterus) and climbing (Astroblepus) catfishes.

Other noteworthy fishes

Astroblepid catfishes (comprising a single genus) have specially adapted suckermouths and pelvic fins that enable them to climb up the faces of waterfalls.

Ecological phenomena

Justification for delineation

This ecoregion falls within the North Andean ichthyographic province defined by Ringuelet (1975), and within the Andean ichthyographic region defined by Gery (1969). Because astroblepid catfishes are distinct components of high-elevation freshwaters along the Andes forefront, that family’s distribution was critical to informing the delineation of the high Andean ecoregions. It is also distinguished by rivers that drain into the Amazon Basin.

Level of taxonomic exploration

Poor