Deserts teem with biodiversity, if you know where to look

California, or rather the California Floristic Province, is a global biodiversity hotspot. That means it hosts an incredibly large number of species of plants and animals found nowhere else on the planet. It is also threatened by environmental degradation. The same is true of the Tropical Andes, Brazil’s Cerrado, the island of Madagascar, and the mountains of Central Asia, a range the early Persians referred to as the “roof of the world.” Notably absent from most lists of biodiversity hotspots? Deserts.

At first, that is perhaps understandable. Deserts are typically thought of as lifeless wastelands, low in diversity both of plants and of animals. Life requires water, and deserts don’t have much. But the truth is that deserts teem with life, if you know where to look, and, critically, when to look. The problem with most common approaches to identifying biodiversity hotspots is that they are defined at the global or continental levels. While deserts can be home to a tremendous amount of endemic species, they’re usually clustered in very small localities, often around ephemeral sources of water.

Take the Sahara Desert, the largest warm desert on the planet. Together with the neighboring Sahel Desert, the Sahara-Sahel ecosystem hosts an impressive number of endemic species. The problem is they’re restricted to a number of small and fragile humid habitats, tiny oases of life punctuating the vast expanse of desert. And human activities threaten those oases, seasonal rivers, and lakes. And that, in turn, threatens the species that have come to rely on them. “As such, those within the Sahara-Sahel may constitute local hotspots of biodiversity under threat,” writes graduate student researcher Cândida Gomes Vale in a recent issue of PLoS ONE. Together with her colleagues, she’s hoping to characterize the importance of mountain rock pools, called gueltas, in Mauritania.

Gueltas are tiny. They can be as small as just 100 square meters or so, and water is only present during the wet season, from July through September. Severe droughts in the 1970s have already rendered many of the northernmost gueltas in Mauritania completely dry year-round. As a result, many of the once-nomadic humans have become more sedentary around more predictable gueltas. That exacerbates the shortage of water in the dry season and results in fecal contamination by domestic animals. The wildlife that’s come to rely on gueltas for survival is increasingly threatened.

Over several years, Vale assessed 69 different gueltas. Each guelta got a complete vertebrate biodiversity workup by no fewer than three researchers, along with nets, traps, and cameras. In addition to animals themselves, they took note of tracks, prints, burrows, and fecal deposits. Because animals don’t usually sit still in one spot, the monitoring “zone” around each guelta extended two kilometers for fishes, amphibians, and reptiles, and five for mammals. The “surrounding area” extended fifty kilometers from the gueltas, thereby capturing information from mountain-dwelling animals who could potentially reach gueltas, corresponding to the likely maximum dispersal distance of any species occurring around the water. In addition, relying on a set of guidelines developed by the IUCN, Vale quantified both the type and number of threats affecting each individual guelta.

In all, Vale recorded 59 vertebrate species using gueltas, and there were no significant differences in animal presence from mountain to mountain. A whopping 78% of Mauritania’s endemic species – those that are found there and nowhere else – were recorded visiting the gueltas. While they did not observe any species that the IUCN has classified as threatened, most of the species that use gueltas remain “Not Evaluated” by the IUCN, making the IUCN list fairly useless when it comes to identifying the conservation status of those animals. That’s to say nothing of all the invertebrates, or the bats, which are also associated with the gueltas.

To put the numbers into perspective, four in five of the country’s endemic species are contained in an area representing just 0.00004% of the country’s surface area. “Gueltas are local hotspots of biodiversity deserving global attention,” write the researchers. Only two-thirds of the gueltas the researchers visited had any sort of legal protection. Of those sites that the researchers deemed as conservation priorities, those numbers were worse: 80% are currently unprotected.

The problem is that Mauritania is also considered a “Low-Income Food-Deficit Country.” Livestock play a crucial role for the people of the country, and they need land and water. So the solution is not to simply encircle all the gueltas in a national park. To simultaneously protect biodiversity and to enhance sustainable development, the researchers argue that the gueltas of highest conservation priority deserve protection, while channels could direct water to troughs further away, reducing both human and livestock pressure on them. “Such infrastructures would also allow decreasing [fecal] contamination of the water, contributing to public health,” they say, as well as to wildlife health. And since the most easily accessible gueltas have crocodiles, the most charismatic of reptiles, there is a possibility for organized ecotourism as a means of infusing the area with added revenue.

The gueltas of the Sahara-Sahel are disproportionately important reservoirs of global biodiversity for their size and will likely become increasingly important refuges for wildlife in the face of climate change. Given that, perhaps they ought to be considered when making decisions about conservation priorities at the global or continental levels. – Jason G. Goldman | 13 March 2015

Source: Vale C.G., S.L. Pimm & J.C. Brito (2015). Overlooked Mountain Rock Pools in Deserts Are Critical Local Hotspots of Biodiversity, PLOS ONE, 10 (2) e0118367. DOI: 10.1371/journal.pone.0118367.

Header image: Camels in a guelta in Chad, via Wikimedia Commons/Dario Menasce.

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