Boundaries

This ecoregion extends from the Río Colorado in the north to the Tierra del Fuego in the south, including the eastern and western slopes of the southern portion of the Andes and the Atlantic drainages of Patagonia. It also includes the Falkland Islands (Isla Malvinas).

Topography

Patagonia lies on a large depression-scarred plateau that slopes gently toward the Atlantic Ocean. Tablelands, composed of basaltic plateaus and coarse grain fans originating from the Andes, are common (Llames & Zagarese 2009). Elevations rise from sea level along both coasts to peaks above 4600 m asl in the Andean Cordillera (Hijmans et al. 2004). High cliffs line the east coast, with plateaus formed by sedimentary rocks and lava flows, punctuated by hills of resistant crystalline rocks. The Andes extend down the Pacific Coast into Tierra del Fuego where the coastline is defined by inlets and fjords, as well as thousands of islands forming numerous archipelagos. Volcanoes such as Yate, Hornopirén, Michinmahuida, Corcovado, Yanteles, Melimoyu, Mentolat, Cay, Macá, Lautaro, Viedma, Aguilera, Reclus, Monte Burney, and Cook Island line the western slopes of the Andes. Many of these have a large amount of snow cover due to a cool climate and high precipitation. South of latitude 47 ºS volcanoes are more widely spaced, and much of the topography is covered by Patagonian ice fields (Clapperton 1994). The southernmost Andes consist of Late Palaeozoic to Early Mesozoic metamorphic basement (Moreno & Gibbons 2007). The northern limit comprises a complex volcanic zone called La Payunia with more than 700 volcanic cones and extensive recent lava flows cutting across the mid-upper Río Grande valley.

Freshwater habitats

Of the many rivers that once cut deep, wide valleys across Patagonia from the Andes to the Atlantic, only a few permanent streams remain, including Río Colorado, Rio Neuquen, Rio Limay, Río Negro, Río Chubut, Río Senguerr, Río Chico, and Río Santa Cruz. Most are either intermittent or completely dried out along all or part of their course, such as the Río Deseado, or otherwise end in salt flats.  

There are also many lakes of tectonic, periglacial, volcanic, eolic, or karstic origins that range from shallow to deep, and from intermittent to permanent (Markgraf 1988). The deepest lakes occur in the Patagonian Andes and range from ultraoligotrophic to oligotrophic, whereas those on the Patagonian Plateau are shallower and range from mesotrophic to eurotrophic (Quirós & Drago 1999). Most notable are glacier lakes that occur at the eastern base of the Andes. North of Lake Nahuel Huapí, most of these lakes drain to the Atlantic, whereas those to the south (including lakes Gral Carrera-Buenos Aires, Cochrane/Pueyrredón, and O\'Higgins/San Martín) primarily drain to the Pacific through short, deep canyons. Lakes Viedma and Argentino, in contrast, follow slower, longer courses to the Atlantic. Immense glaciers occur in southern Patagonia; for example, Perito Moreno is 5 km wide, 30 km long, and 60 m high (López et al. 2002).

Terrestrial habitats

This ecoregion spans a handful of terrestrial ecoregions including low monte in the northeast, Patagonian steppe through the center of the ecoregion, and Valdivian temperate and Magellanic subpolar forests along the west and southern coast. The dominant plant communities in the Patagonian steppe include semi-desert and shrubby steppe, with cushion plants and grassy steppes dominating the more humid areas. Dense graminaceous and cyperaceous prairies known as vegas grow in the valleys in the form of bogs (López et al. 2002). Halophytic species of genera like Distichlis, Nitrophila, and Puccinellina reside in saline areas (WWF 2001).

The Magellanic subpolar forests extend along the Southern Andes and Chilean Archipelago from southern Aisén to Tierra del Fuego and Isla de los Estados. The dominant plant species are evergreen Magellan’s beech (Nothofagus betuloides) in the west and deciduous Antarctic beech (N. antarctica) and lenga beech (N. pumilio) in the east. Permanent snow, ice caps, and glaciers occur at higher elevations. Magellanic moorland occurs in the colder areas to 48 ºS, and is characterized by dwarf shrubs, cushion plants, grass-like plants and bryophytes (WWF 2001).

Description of endemic fishes

The ecoregion contains one endemic genus and six endemic species that represent approximately a third of the species of Patagonia. The naked characin (Gymnocharacinus bergii) is the only species of the endemic genus Gymnocharacinus. It comes from northern Patagonia and is endangered due to the reduction of its habitat (IUCN 2010). Other endemics include the catfish Olivaichthys  viedmensis and O. mesembrinus, largemouth perch (Percichthys colhuapiensis), creole perch (P. altispinis), and the atherinopsid, Odontesthes hatcheri.

Other noteworthy fishes

The genus Percichthys is restricted to the Patagonian region in the Cuyan - Desaguadero [340], South Andean Pacific Slopes [341], Bonaerensean Drainages [347], Patagonia [348], and Valdivian Lakes [349] ecoregions. The family Diplomystidae (represented by the genus Diplomystes) is also restricted to the Patagonian region in the ecoregions 340, 341, 348, and 349.

Many of the fish of this ecoregion have suffered declines due to habitat modification as well as predation and competition for food and habitat through the introduction of salmonid species like brook trout (Salvelinus fontinalis), land-locked salmon (Salmo salar sebago), brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), and Chinook salmon (O. tshawytscha) (Arismendi et al. 2009; López et al. 2002).

Ecological phenomena

Lampreys (Geotriidae) and galaxiids (Galaxiidae) in Patagonia are characterized by diadromous species that spend part of their life cycle in the open ocean. Examples include both species of Aplochiton, which spend their juvenile period at sea; the widely distributed inanga (Galaxias maculatus), which lives at sea for months to years; and the Chilean lamprey (Mordacia lapicida), which spends several years at sea (McDowall 2002).

Justification for delineation

Patagonia falls within Ringulet’s Patagonia ichthyographic province within the Austral subregion, emphasizing a fish fauna distinct from that of the Brasilic subregion (Ringuelet 1975). Climatic conditions, recent origin, altitude, and irregular flow of rivers contribute to the depauperate freshwater fauna of Patagonia and its dissimilarity to other parts of South America (Gery 1969). It includes primitive forms that originated from southern cold waters as well as diadromous forms, such as galaxiids and lampreys (López et al. 2002).

Level of taxonomic exploration

Fair