Abstract
A natural laboratory is a place supporting the conditions for hypothesis testing under non-anthropogenic settings. Located at the southern end of the Magellanic sub-Antarctic ecoregion in southwestern South America, the Cape Horn Biosphere Reserve (CHBR) has one of the most extreme rainfall gradients in the world. Subject to oceanic climate conditions, it is also characterized by moderate thermal fluctuations throughout the year. This makes it a unique natural laboratory for studying the effects of extreme rainfall variations on forest bird communities. Here, we monitor the bird species richness in the different forest types present in the CHBR. We found that species richness decreased with increasing precipitation, in which an increase of 100 mm in average annual precipitation showed about 1% decrease in species richness. Similar patterns were found among different forest types within the CHBR. These results provide a baseline to investigate the interactions between physical and biotic factors in a subpolar region that climatically contrasts with boreal forests, which is subject to continental climatic conditions. This research highlights the importance of ecological and ornithological long-term studies in the CHBR, which can contribute both to a higher resolution of the heterogeneity of climate changes in different regions of the world, and to orient conservation policies in the Magellanic sub-Antarctic ecoregion in the face of growing development pressures.
Highlights
A natural laboratory is a place that is sustained by multiple social, cultural and institutional dimensions, but a key feature is holding a unique set of geographic and/or biophysical attri-Communicated by Adeline Loyau
The Cape Horn Biosphere Reserve (CHBR) protects 50,000 km2 of which 19,172 km2 are terrestrial ecosystems (Rozzi et al 2006). It is located at the southern end of the sub-Antarctic ecoregion (Rozzi et al 2012), where the dominant habitats are represented by forests of coigüe (Nothofagus betuloides), lenga (N. pumilio), ñirre (N. antartica), mixed Nothofagus forests, Magellan tundra complex (Sphagnum spp.), high-Andean regions, rocky outcrops, glaciers and scrublands, the latter predominantly composed of Berberis sp., Ribes magellanicum, Embothrium coccineum, Drimys winteri, Chiliotrichum diffusum and Gaultheria XXXucronate (Pisano Valdés 1977; Rozzi and Jiménez 2014)
More generalist species were found in 100% of the monitoring sites, such as the Thorn-tailed Rayadito (Aphrastura spinicauda), Patagonian SierraFinch (Phrygilus patagonicus), Rufous-collared Sparrow (Zonotrichia capensis chilensis), White-crested Elaenia (Elaenia albiceps chilensis), Dark-bellied (Cinclodes patagonicus) and Buff-winged Cinclodes (Cinclodes fuscus), Black-chinned Siskin (Spinus barbatus), and Austral Thrush (Turdus falcklandii magellanicus)
Summary
A natural laboratory is a place that is sustained by multiple social, cultural and institutional dimensions, but a key feature is holding a unique set of geographic and/or biophysical attri-Communicated by Adeline Loyau. In this article we focus on an outstanding attribute, which has not been sufficiently investigated so far, the extreme rainfall gradient. This gradient span west to east, ranging from > 5,000 mm to < 500 mm of rainfall per year (Aguirre et al 2021). This represents a unique situation worldwide, where in a west-east distance of 500 km of fjords, channels and islands, from the Pacific Ocean towards the Atlantic Ocean, rainfall decreases by an order of magnitude (Rozzi et al 2004; Tuhkanen et al 1990)
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