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Equids engineer desert water availability

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Science  30 Apr 2021:
Vol. 372, Issue 6541, pp. 491-495
DOI: 10.1126/science.abd6775

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Digging for water

Water is scarce in dryland ecosystems. Some larger animals in these regions dig wells that may provide water to other species. This behavior may have been common among megafauna that are now extinct, especially in North and South America, where megafaunal extinctions were the most severe. Lundgren et al. tested whether feral equids (horses and donkeys) reintroduced to desert regions in the North American southwest dig wells that provide ecosystem-level benefits. They found that equid-dug wells increased water availability, were used by a large number of species, and decreased distance between water sources. Abandoned wells also led to increased germination in key riparian tree species. Such equid-dug wells improve water availability, perhaps replacing a lost megafaunal function.

Science, this issue p. 491

Abstract

Megafauna play important roles in the biosphere, yet little is known about how they shape dryland ecosystems. We report on an overlooked form of ecosystem engineering by donkeys and horses. In the deserts of North America, digging of ≤2-meter wells to groundwater by feral equids increased the density of water features, reduced distances between waters, and, at times, provided the only water present. Vertebrate richness and activity were higher at equid wells than at adjacent dry sites, and, by mimicking flood disturbance, equid wells became nurseries for riparian trees. Our results suggest that equids, even those that are introduced or feral, are able to buffer water availability, which may increase resilience to ongoing human-caused aridification.

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