A dynamic perspective of shallow lakes of arid Patagonia as habitat for waterbirds

Abstract

In arid regions, where water availability imposes significant constraints onmany species, shallow lakes and ponds have a particularly importantecological role. Meanwhile, these aquatic environments have been listedamong the most threatened habitats of the world. With an area of over6.000.000 km2, the Patagonian steppe is one of the largest arid extensions ofSouth America. Running intermittently along the steppe, a system of basalticplateaus or mesetas, holding thousands of lakes and ponds, provides primaryhabitat for numerous species, including a rich waterbird community andnumerous endemism. We characterized the array of shallow lakes of theStrobel meseta, analyzing their dynamics along temporal and spatial gradients.Using multivariate analyses, based on limnological, topographic, andgeographic variables of 32 water bodies, we identified four lake types: largeunvegetated, large vegetated, turbid, and ponds. Based on 114 bird censuseswe evaluated the relative importance of each lake type as waterbird habitat.Ponds hold the highest density of waterbirds and, together with large vegetatedlakes, the highest number of species. Using satellite images corresponding toperiods with contrasting precipitation, we analyzed the hydrologic dynamic bylake type and by location throughout the meseta. Whereas most lakes,including large ones, are concentrated on the west side of the meseta, above900m of elevation, ponds are distributed throughout the whole area, but areless stable from a dynamic point of view. The total area covered with water onthe meseta is strongly affected by seasonal and inter-annual changes inprecipitation. During dry periods, most ponds, and particularly those located atlower altitudes, undergo a drastic reduction in water level or even dry out.Variations in water level impinge on the limnological configuration of lakesand ponds, particularly on the emergence of macrophytes, a key habitatattribute for most species of waterbird. Given this strong dependency ofhydrology and habitat provision on precipitation, temperature, and wind,meseta shallow lakes and the communities they sustain appear particularlyvulnerable to climate change.