BIOGEOGRAPHY OF CHILEAN ICHNEUMONID FLIES (HYMENOPTERA: ICHNEUMONIDAE)
BIOGEOGRAFIA DE LOS ICHNE UMONIDAE CHILENOS (HYMENOPTERA: ICHNEUMONIDAE)
Author
Porter, Charles C.
Abstract
from the 24lh to the 18lh parallel (continuing northward almost to the equator as the Peruvian CoastalDesert and Precordillera) and (2). The Neantartic Realm including all Chile south of the 25lh parallel aswell as a narrow strip of western Argentina south or the 38,h parallel.Below 3000 m, the Northern Province is an almost absolute desert, where life is confined to rivervalleys and oases. These lowland refugia are inhabited by a depaupérate biota with few endemic butmany Neotropic, Andino-Patagonian, and Cosmopolitan genera although with numerous endemicspecies. Between 2000-3500 m most of the Neotropic genera disappear, but from 3000 m to theshowline annual precipitation increases and allows development of a diverse Andino-Patagonian floraand fauna similar to that of the central Andes in Perú and Bolivia but with a large component ofendemic species and subspecies.The Neantarctic Realm embraces habitats from semidesert in the north through sclerophyllwoodland at intermediate latitudes to humid Nothofagus Forest below the 38lh parallel. TheNeantarctic biota differs strongly from that in the rest of South America and can not be included as asubelement of the Neotropic. It has 121 ichneumonid genera of which 39 (32%) are endemic, 31 (26%)Cosmopolitan, 20 (16.5%) Holarcticor Holarctic-Oriental, 17 (14%) Neotropic, 8 (6.6%) Andino-Patagoniawith frequent representation in the Coastal mountains of south Brasil, 4 (3,3%) transantarcticwith species in Neantartic Chile as well as in Australia and sometimes also New Zealand, and with 3genera (2.4%) widely but disjunctly distributed in both the Northern and Southern Hemispheres.Clearly, the outstanding anomalies of the Neantarctic ichneumonid fauna are its exceptionally highnumber of endemic genera and its surprisingly few Neotropic genera for an area in geographicproximity to the American Tropics.It is hypothesized that the main lineages within the Ichneumonidae were already present in theCretaceous, at a time when the world’s continents were still united by land bridges and the globalclimate was rather uniformly humid and much warmer than at present. A diverse biota evolved onAntartica at this time and was extensively shared with Southern South America and Australia up to theEocene. The aberrant and endemic biota of Neantarctic South America probably represents survivorswhich moved north from Antartica before that continent’s glaciation. By the middle Tertiary,mountain building, desertification, and coid climatic pulses had isolated the Neantarctic Realm allalong its eastern and northern boundaries, so that its biota has evolved in isolation for perhaps the last40 million years. Lack of biotic continuity between Neantarctic semideserts and the spatially adjacentNorth Chilean and Peruvian Coastal Desert seems hard to explain. How Southern AntofagastaProvince between 24-24 degrees south is extremely dry and is occupied by several mountain chainsaveraging 2-3000 m in altitude and extending almost to the coast. This is the only barrier of its kindalong Pacific South America between the equator and Tierra del Fuego. During later Tertiary andPleistocene coid periods, these mountains must have been glaciated, or both very coid and very dry, sothat the Neantarctic biota could retreat no farther north at times of clima-deterioration from otherSouth American lineages, locked by physical and climatic barriers into a narrow strip along the PacificCoast and west of the Andes between Tierra del Fuego and Antofagasta.