Donkeys and wild horses use their hooves to dig wells up to two meters deep in search of water. These wells are then reused by other species and encourage vegetation development. A team of scientists led by Erik Lundgren, a research biologist at Sydney University of Technology, investigated this curious phenomenon. This type of behavior had already been noticed by biologist Erick Lundgren while working in western Arizona, where he was studying river systems at the time.
Originally, a species considered invasive
In these arid ecosystems, which make up a third of the Earth’s surface, water remains the most limited resource. Its availability shapes the distribution of species, but also their development, and thus the overall structure of the food chain that rules there. The ability of animals to improve water availability by bringing it to the surface has so far been of little interest. Already observed in Australia and North America, it has never been rigorously studied.
Europeans introduced by coming to America, donkeys and horses have long been used as a means of transportation. But in the deserts they were quickly abandoned, when their use was no longer needed, and then they were considered invasive species. What makes their contribution to these deserts even more interesting, “because donkeys and horses are considered agents that harm biodiversity”, who is not a species native to the region, he said.
On Tkings of the year of study, 57 different species drank from wells
To study the impact of ungulate abysses on ecosystems, a team of scientists studied the Sonoran and Mojave deserts in North America. These two deserts, located in the western United States, have a total area of approximately 350,000 km². At these research sites, researchers mapped the distribution of rivers and wells dug by ungulates, and then over three summers observed cameras moving species in each of these sites.
Theirs observations demonstrate the usefulness of these wells, which not only improve the amount of water available, but also reduce the distance between two water points. At the highest heat, in the middle of summer, horse wells even served as the only source of water supply in some dry places. On average, the density of available water was multiplied by three compared to constant water points and could reach 14 times the initial density without wells.
A deer hemion and her calf drink from a well dug by a horse. Credit: Erick J. Lundgren
A total of 57 drinking species were recorded near the source, including lynx, coyotes, birds, and even a black bear. The daily diversity of species compared to control sites was up to 64% higher than that at dry control sites. Wells “they’ve been used by almost every species you can imagine, including some surprising ones like black bears, which you wouldn’t expect to see in the desert.”, he explained.
These wells dug by ungulates also favor vegetation. Many coastal trees have grown near abandoned wells in the Sonoran Desert. Between them, Populus fremontii or “California black poplar,” and Salix gooddingii, called “Gooding’s willow,” two coastal species found only in this region. Their germination requires a moist substrate without competitive vegetation provided by abandoned wells. In addition, Mr.Thanks to the data collected, the scientists found a higher sowing density in equidae than in neighboring wet coastal areas, a difference that persisted beyond the summer periods. Their results therefore suggest that horse wells serve both flora and fauna.
Increasingly important behavior
The ecological importance of this phenomenon seems to depend on the availability of alternative water sources. Intermittent streams, which are the most common type of streams in almost half of the Earth, were the ones in which horse wells had the greatest impact on water availability. Currently, the intermittency of streams increases as perennial rivers and streams lose flow. Dry areas are expanding due to groundwater abstraction, agriculture and climate change. These reductions in water availability, associated with rising temperatures, will have significant effects on biodiversity and ecosystem functioning. A study conducted by Erick Lundgren and his team shows that the behavior observed in equidae could mitigate these changes, whether native or introduced on the continents.