Southwest Deserts 
Although the Southwest Deserts are characterized by severe conditions of low rainfall, periodic drought, high winds and daily fluctuations of extreme cold and heat, they also contain rich biodiversity and species uniquely adapted to deserts. Four unique desert communities—the Sonoran, Mojave, Chihuahuan, and Great Basin deserts—span Nevada, Arizona, New Mexico and southern California. The Sonoran Desert alone contains approximately 5,000 plant species, 600 species of vertebrates and thousands of invertebrates, including 1000 native bee species. More than 500 of the world’s 1,500 cacti species are in the Chihuahuan desert. In North America, the region’s threat from global warming is second only to the Arctic, and the ecosystem’s fast growing urban areas and increased use of severely limited water are forcing many species to the brink of extinction.
A Home for Threatened and Endangered Species
The Southwest deserts are a hotspot for endemism (species found nowhere else) and are home to an incredible diversity of threatened and endangered plants and animals—23 species in just one Sonoran desert county alone. Because many species are adapted to very specialized niches, their survival is fragile. The Desert tortoise and Sonoran pronghorn antelope depend on this ecosystem. Declines in endangered long-nosed and long-tongued bats, essential for pollination of the agaves, may put the long-term survival of the agaves at risk. Arid-adapted rodents, kangaroo rats, kangaroo mice and pocket mice, found in all four deserts, are threatened or endangered. One endangered plant, six threatened plants, four species of endangered pupfish and one threatened aquatic beetle live in the Great Basin desert’s Ash Meadows National Wildlife Refuge.
Aquatic species inhabit marshes and pools, fed by rainfall and springs, that dot the landscape. Forty-two imperiled freshwater mollusks called springsnails, which are key to food production, water chemistry, and nutrient cycling, live in the Great Basin and Mojave deserts. If these small species were to disappear, the effect would be catastrophic for the food chain.
Climate Change Threats
The temperature increase and precipitation changes in Southwest deserts is the most severe in the United States. The increase in duration and severity of droughts threaten to make the Dustbowl and 1950’s drought climates the new norm, threatening both terrestrial and aquatic species. For instance, the Quitobaquito pupfish, found only in a 1/2-acre Arizona pond, could see its home heat up or dry up. Desert pupfish can survive in 110-degree, saline water, but their eggs may not survive the increased temperatures. Desert tortoises already face numerous threats, and they cannot tolerate the additional stressors of droughts, heat waves and changing vegetation brought about by climate change. With a wild population that has fluctuated around 100 in Arizona, the Sonoran pronghorn antelope is threatened by the increased droughts, which limit surface water and eliminate food resources.
Needed Conservation Measures
The Desert National Wildlife Refuge Complex—including four wildlife refuges in southern Nevada—is part of the U.S. Fish and Wildlife Service’s new Landscape Cooperative Conservation initiative. (The initiative forms management-science partnerships to inform resource management for climate change and other stressors.) However, existing refuges are inadequate for this ecosystem. Ongoing threats come from urban sprawl, cattle grazing, mining, dam building, and off-road vehicles. And climate change is worsening invasive species impacts. Highly combustible invasive plants in the drier conditions are leading to greater fire frequency and severity, which harm the ecosystem and its species, such as fire-intolerant native cacti. Furthermore, unsustainable water use from explosive population growth combined with the increasing drought severity threatens to leave desert ecosystems
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