Sharp altitudinal gradients in Magellanic Sub-Antarctic streams: patterns along a fluvial system in the Cape Horn Biosphere Reserve (55°S)

Abstract

Magellanic Sub-Antarctic streams run through steep, low-altitude mountainous gradients characterized by a topography that supports a mosaic of evergreen, mixed, and deciduous forests, peat lands, and scrublands. Here, the macroinvertebrate fauna and their ecological interactions are poorly known. This study linked the distribution, community composition, and functional feeding structure of benthic macroinvertebrates with physicochemical and thermal patterns along the altitudinal gradient of a Magellanic Sub-Antarctic watershed. Invertebrates were collected during the austral summers of 2008, 2009, and 2010 at five different altitudes. Our results indicate that benthic macroinvertebrate community distributions are predominantly affected by temperature and certain species show distribution restrictions through the altitudinal gradient studied. Temperature profiles indicate that this Sub-Antarctic watershed is characterized by a sharp thermal gradient, in which cumulative degree-days (°C) per year sharply increase through a relatively short altitudinal gradient (0–600 m above sea level). With the results from this study, we can now study thermal tolerances of altitude-restricted species or project changes in their distributions and voltinism patterns according to climate change scenarios. Ecosystems at higher latitudes and altitudes are experiencing some of the fastest rates of warming on the planet, and Magellanic Sub-Antarctic watersheds could be considered as “sentinel systems,” providing early warning of wider scale change.