Track Analysis Reveals the Composite Nature of the Andean Biota

Abstract

The Andean subregion corresponds to south-western South America below 30˚S latitude, extending through the Andean highlands north of this latitude, and comprises five provinces: Subantarctic, Central Chilean, Patagonian, Puna and Paramo. Based on a track analysis of the Andean biota, three main types of distributions were found: (1) no relationship of the Andean subregion with other areas (Andean endemic distributions); (2) relationships with one area or subregion, namely (a) Austral, (b) Tropical and (c) Amphitropical distributions; and (3) relationships with more than one subregion (cosmopolitan distributions). These relationships were described and mapped as individual tracks, based on data from plant and animal taxa. Coinciding individual tracks constitute generalised tracks, which follow three basic patterns: Andean endemic, Austral and Tropical. The first pattern is represented by three generalised tracks, namely (a) along the Puna, Central Chilean, Subantarctic and Patagonian provinces; (b) along the Central Chilean, Patagonian and Subantarctic provinces; and (c) in the Subantarctic and Patagonian provinces. The second pattern (Austral) is represented by two generalised tracks: (a) along the Subantarctic province of South America, south-eastern Australia, and New Zealand and (b) along the Subantarctic province and New Zealand. The third pattern (Tropical) is based on three generalised tracks joining (a) all the Andean subregion with the Neotropical subregion; (b) Paramo and Puna provinces, and the Neotropical subregion; and (c) Patagonian province and Neotropical subregion. The Austral pattern reflects the existence of an ancient Austral biota, with Gondwana events likely to have played a major role in its evolution, whereas the origin of the Neotropical pattern is probably linked to a more recent history, especially the uplift of the Andes and further glaciations. Both of these patterns reveal that the biota of the Andean subregion has a complex or hybrid origin where two different ancestral biological and geological worlds met and combined. The Puna, Patagonian, and Subantarctic provinces appear as panbiogeographic nodes, because of the numerous tracks that cross them, probably due to complex geological events. It is possible that the patterns analysed are the consequence not only of vicariant events promoted by tectonic phenomena, but also of dispersal and/or extinctions that have concealed these events.