Abstract

Plant species distributed along the altitudinal gradient above treeline are adapted to a wide range of temperature conditions over a short physical distance, these telescoping conditions found over many degrees of latitude.Given that species with wider altitudinal ranges exhibit broader temperature niches than altitudinally narrowly distributed species, the probability of successful colonization/migration should be greatest in species with broad altitudinal ranges (Increased colonization probability hypothesis). Using presence and abundance records for 100 m altitudinal intervals on four mountains located at increasing distances eastward of the Southern Patagonian Icefield at the same latitude, we tested the hypothesis that alpine species with broader altitudinal ranges on the eastern source mountain for postglacial colonization are more likely to be successful colonizers on mountains closer to the Patagonian icefield exposed for less time since the retreat of the ice. Altitudinal range size was significantly correlated with number of mountains recolonized, but local abundance on the putative source mountain was not. These results suggest that niche breathe rather than source size determines colonizing ability. With these results in hand, we began investigating the increased colonization probability hypothesis at a biogeographical scale using georeferenced data base herbarium records for the genus Senecio, the largest genus in the alpine zone in the South American Andes. In Senecio, available data suggests that latitudinal range (a proxy of colonization success) is positively correlated with altitudinal range in puna species. The results in Senecio are interesting given that altitudinal and latitudinal ranges obtained from herbarium data base records are imperfect. That the tendency in Senecio was found in a pool of species which necessarily represent different evolutionary ages suggests the possibility of a hitherto undetected ecological rule in the alpine. Studies on many other genera and for a random sample of the high elevation flora are needed to confirm the generality of these findings, a goal that is attainable given the existence of electronic data bases such as the Chilean flora data base, and TROPICOS.