Author's personal copy Polar Biol DOI 10.1007/s00300-015-1746-4 ORIGINAL PAPER Sharp altitudinal gradients in Magellanic Sub-Antarctic streams: patterns along a fluvial system in the Cape Horn Biosphere Reserve (55°S) 1,2,3,6 1,2,3,4 1,2,3,5,6 Tamara Contador • James H. Kennedy • Ricardo Rozzi • Jaime Ojeda Villarroel1,2,3,6 Received: 17 July 2014 / Revised: 20 June 2015 / Accepted: 22 June 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract Magellanic Sub-Antarctic streams run through Antarctic watershed is characterized by a sharp thermal steep, low-altitude mountainous gradients characterized by gradient, in which cumulative degree-days (°C) per year a topography that supports a mosaic of evergreen, mixed, sharply increase through a relatively short altitudinal gra- and deciduous forests, peat lands, and scrublands. Here, the dient (0–600 m above sea level). With the results from this macroinvertebrate fauna and their ecological interactions study, we can now study thermal tolerances of altitude- are poorly known. This study linked the distribution, restricted species or project changes in their distributions community composition, and functional feeding structure and voltinism patterns according to climate change sce- of benthic macroinvertebrates with physicochemical and narios. Ecosystems at higher latitudes and altitudes are thermal patterns along the altitudinal gradient of a Mag- experiencing some of the fastest rates of warming on the ellanic Sub-Antarctic watershed. Invertebrates were col- planet, and Magellanic Sub-Antarctic watersheds could be lected during the austral summers of 2008, 2009, and 2010 considered as ‘‘sentinel systems,’’ providing early warning at five different altitudes. Our results indicate that benthic of wider scale change. macroinvertebrate community distributions are predomi- nantly affected by temperature and certain species show Keywords Altitudinal gradient Benthic distribution restrictions through the altitudinal gradient macroinvertebrate Sub-AntarcticÁ Functional feeding Á Á studied. Temperature profiles indicate that this Sub- group Climate change Á Introduction Electronic supplementary material The online version of this article (doi:10.1007/s00300-015-1746-4) contains supplementary The Sub-Antarctic Magellanic ecoregion, immersed within material, which is available to authorized users. the South American temperate forest biome, has been identified as one of the 24 true wilderness areas remaining & Tamara Contador [email protected]; [email protected] on the planet. More than 70 % of the original vegetation cover is still extant, over an area greater than 10,000 km2, 1 Universidad de Magallanes, Avenida Bulnes, which lacks significant industrial and urban development 01855 Punta Arenas, Chile (Mittermeier et al. 2003). It spans a myriad of archipela- 2 Sub-Antarctic Biocultural Conservation Program, goes from 47°S to 56°S unique in the world, in a latitudinal Punta Arenas, Chile range of almost 10° well to the south of the southernmost 3 Omora Ethnobotanical Park, Puerto Williams, Chile forests in New Zealand and Australia (Rozzi et al. 2012). 4 Department of Biological Sciences, University of North Furthermore, South American Sub-Antarctic ecosystems Texas, Denton, TX, USA sharply contrast with their northern hemisphere latitudinal 5 Department of Philosophy and Religion Studies, University counterparts in terms of the land-to-ocean ratio, generating of North Texas, Denton, TX, USA sharp inter-hemispheric climatic and biotic differences in 6 Instituto de Ecologı´a y Biodiversidad-Chile, Santiago, Chile temperate and subpolar latitudes (Rozzi et al. 2012). 123 Author's personal copy Polar Biol Southern South America’s Sub-Antarctic freshwater the heterogeneity in habitats and marked gradients in ecosystems temperature and rainfall over a relatively small land area (Rozzi et al. 2012). Among the freshwater fauna, inverte- South America’s Sub-Antarctic freshwater ecosystems are brates are strongly affected by thermal variation across positioned in a region shaped by the glacial erosion of the latitudinal and altitudinal scales (Sweeney et al. 1990). The continent during the Last Glacial Maximum, between thermal environment directly affects their metabolism and 23,000 and 19,000 BP (Hulton et al. 2002). In contrast with growth rates, and hence their ability to survive when high-latitude environments in the northern hemisphere, temperature variation exceeds their range of thermal tol- these ecosystems present marked changes in microclimate erance (Ward and Stanford 1982). Thus, obtaining basic with small changes in elevation. The modulating effect of information about the diversity, distributions and life his- the ocean drastically diminishes with altitude, and the tree tory of freshwater benthic macroinvertebrates associated line appears at only 600 m above sea level (Rozzi et al. with Magellanic Sub-Antarctic rivers are extremely 2010). These steep altitudinal gradients are characterized important to assess the possible implications of climate by a diverse topography that supports evergreen forests, change in this region of the world. mixed evergreen/deciduous forests, peat lands, grasslands, The goals of this study were to: (1) provide a concise and scrublands over a relatively small area (Pisano 1980). description of the benthic fauna associated to the steep Marked topographic and climatic barriers have isolated this altitudinal gradient of a Sub-Antarctic fluvial system in the austral vegetation from the nearest subtropical forests by Cape Horn Biosphere Reserve, Chile (55°S); (2) to assess 1500–2000 km, generating high levels of endemism and a the relationships between richness, density, and distribution unique biodiversity of vertebrates, invertebrates, and non- of benthic macroinvertebrates with temperature and other vascular and vascular plants (Armesto et al. 1998; Rozzi physicochemical variables along the altitudinal gradient; et al. 2012). For example, close to 90 % of woody plant and (3) to provide the basis for future research regarding species, 33 % of woody genera, and about 60 % of bryo- southern South American Sub-Antarctic freshwater phyte species (mosses and liverworts) are endemic to this ecosystems in the context of climate change. region (Rozzi et al. 2012). Indeed, the Sub-Antarctic ecoregion is a ‘‘hotspot’’ of bryophyte biodiversity, one factor that led UNESCO to declare the territory and its Materials and methods waters the Cape Horn Biosphere Reserve. Overall, though, despite the unique biogeographic setting and the high fre- Study area quency of endemisms encountered to date, the biological richness of the Cape Horn archipelago and the Magellanic The Ro´balo River (54°S, 067°W), with an extension of Sub-Antarctic ecoregion is understudied (Contador et al. approximately 12 km, runs through the altitudinal gradient 2012). Many areas have not been systematically explored, of the Dientes of Navarino mountain range, located on even on small, well-defined, and accessible land masses, Navarino Island (55°S). The river provides drinking water and many of the less charismatic taxa, such as aquatic to the city of Puerto Williams, Capital of the Chilean insects, have barely been surveyed at all (Convey and Antarctic Province and the world’s southernmost town. Stevens 2007; Contador et al. 2012). Navarino Island lies south of the Beagle Channel and north Furthermore, climate change is affecting not only polar of Cape Horn (Fig. 1). The Cape Horn archipelago became regions but also subpolar regions. For example, models of the Cape Horn Biosphere Reserve (CHBR) in 2005, and it temperature change for New Zealand predict the shrinking hosts the world’s southernmost-forested ecosystem, and ultimate disappearance of South Island glaciers, encompassing all of the islands south of the Beagle resulting in the lost of habitats suitable for cold-water Channel, as well as the Chilean portion of Tierra del Fuego specialists (Winterbourn et al. 2008). Additionally, Island located south of the highest peaks in the Darwin although the system of South America’s Sub-Antarctic Mountain Range (Rozzi et al. 2010). The study site lies channels and fjords houses one of the most important ice within this biosphere reserve and the Omora Ethnobotani- fields after Antarctica, the loss of mass and freshwater cal Park, part of Chile’s long-term socio-ecological input has been dramatic in recent years due to global research sites (LTSER) network (Rozzi et al. 2010). It warming (Porter and Santana 2003). In this context, the belongs to the Magellanic Sub-Antarctic ecoregion (Mit- Sub-Antarctic islands of southern South America provide a termeier et al. 2003), which has a strong dominance of unique opportunity for understanding the past and present Austral and also Nearctic and Brasilic elements (Mis- climate change in the southern hemisphere to assess its erendino and Pizzolon 2000). consequences to the biota. Comparative studies of the The forests of this region are composed primarily of responses of the biota to climate change are facilitated by three members of the genus Nothofagus (Pisano 1980) and 123 Author's personal copy Polar Biol Fig. 1 Map of Navarino Island showing its location within the Cape Horn Biosphere Reserve. The map details the location of the Ro´balo River watershed, located on the north side of the island. Sampling sites along the watershed are shown are part of the South American temperate forest biome, Puerto Williams is 6.0 °C and 467.3 mm, respectively, and occurring