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In the desert, donkeys and wild horses play an essential role

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Wild donkeys and horses reintroduced to the desert regions of southwestern North America dig wells for water. In reality, they do much more than that, supporting the resilience of many species.

Large terrestrial herbivores suffered extensive extinctions from the end of the Pleistocene. While climate change at the end of the last ice maxima may have played a contributing role, researchers now agree on one fact: most prehistoric losses are due to human activity.

In tropical and temperate ecosystems, we know that these animals played essential roles in their ecosystem. Less is known, however, about how megafauna may have shaped arid ecosystems. However, the latter represent one third of the earth’s surface.

As part of a study recently, researchers have focused on the main limiting and essential resource of these arid zones: water. The team focused on two equines, the wild donkeys and horses that regularly dig wells that can go two meters deep to get water and drink. The aim was toassess the effects of these well digging on the local ecosystem.

The study focused on four rivers fed by groundwater from the sonorous desert. Data was collected every two to four weeks for three summers.

Credit: Sciencemag

Equines maximize water availability

This work has really brought to light the importance of these wells dug by donkeys and wild horses. On each site, the researchers in fact mapped the “background” water (already on the surface) and the water dug by equines. Not surprisingly, wells were especially important for the water supply in midsummer. During this period, temperatures rise sharply and the water table level decreases.

The wells for donkeys and horses have also greatly reduced (up to 65%) the distances between each aquatic area, thus allowing animals to travel fewer kilometers to drink.

An impact on flora and fauna

To understand if these wells were of value to other species, the researchers deployed several camera traps. Thanks to this data, they were able to estimate the daily richness of the species attracted by these wells, but also the frequency and duration of these visits. These results were then compared to the same data collected from sites offering background water, but without wells and adjacent dry “control” sites.

Overall, the researchers detected 59 species of vertebrates in equine wells, of which 57 were recorded drinking. Daily cash wealth was respectively more than 50% higher near wells than near other sites. Likewise, the length of visits was on average 620% longer, and the frequency of visits was at least 60% higher.

The digging of these wells also influences the vegetation. On a dyked perennial river in the Sonoran Desert, abandoned equine pits shelter numerous riparian trees (mainly Populus fremontii and Salix gooddingii).

Here, researchers recorded more seedlings than in adjacent riparian areas. Again, this is good news as the conservation of these fast growing species, whose germination requires a moist substrate without competing vegetation, is considered a regional priority.

For the authors, the finding is clear: although introduced megafauna has primarily been studied as a threat to conservation goals, a growing body of evidence suggests that they can replace lost ecological functions.

In this case, here, the study emphasizes that wild equines can increase water availability in arid areas with associated effects on a variety of animal and plant species.


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