Lessons of Extinction Told Through 2 California Desert Animals

Sonoran mud turtle | Photo: Richard Bonnett/Flickr/Creative Commons License

The sad end of Lonesome George, the last remaining Pinta Island Galapagos Tortoise, is dominating the endangered species news this month, but there's also some related news closer to home: a species native to the California Desert has been added to the "Red List."

The species, the Amargosa springsnail, was added to the Red List within the last year along with about 1,900 other species worldwide. Another California desert species, the Sonoran mud turtle, had its Red List condition upgraded from "Vulnerable" to Near Threatened." That's happier news on the face of it, but with implications worth looking at carefully. Both are threatened by human activity, and the Sonoran mud turtle may well have been eradicated from California. The snail's addition to the list and the turtle's status adjustment both offer lessons about how extinctions, like that of Lonesome George's family, take place.

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The ominous Red List, compiled and maintained by the International Union for Conservation of Nature, includes species and subspecies that have been deemed at risk of extinction by a cooperating consortium of scientific organizations. More than 66,000 species and subspecies are included, assigned threat assessments ranging from "Extinct" to "Least Concern" -- that last meaning "not in trouble the last time we checked."

The Sonoran mud turtle, Kinosternon sonoriense, was once reasonably common in wetlands fringing the western shore of the Colorado from Needles to Mexico. They also lived in irrigation canals in Imperial County. The last report of a Sonoran in California was from the vicinity of Laguna Dam in 1962, and a combination of competition with invasive species and our little bout of building dams on every last mile of the lower Colorado is probably what did California's Kinosternon sonorienses in. Little is known about the California population's behavior. The Arizona population, still more or less intact, may well offer some clues. Adult Sonoran mud turtles reach about 7 inches in length, with high-domed shells ranging from dark gray-brown to a lighter olive color.

Unlike their neighbors the desert tortoise, mud turtles live in water. In fact, that's the distinction between turtles and tortoises in general, a natural history fact that you will remember forever if you listen to this short song by Parry Gripp:

Sonoran mud turtles aren't picky about their watery habitats: they're found in everything from free-flowing rivers to stagnant stock tanks. They may eat a bit of plant material, but they primarily subsist on meat: insects and their larvae, frogs, fish and crayfish, and occasional carrion make up the majority of a mud turtle's diet.

The turtle's adaptability, and its having been found in a number of new places since its addition to the list in 1996, is what prompted its happily upgraded status. But the IUCN minces no words about the long-term threats to the turtle's survival as a species:

The Amargosa springsnail's addition to the list is, of course, sadder news. Known to malacologists as Pyrgulopsis amargosae, this springsnail is known from just five locations in the lower Amargosa River basin, including Saratoga Springs in Death Valley.

Saratoga Springs in Death Valley | Photo: Mike Baird/Flickr/Creative Commons License

This species is one of 133 species in the genus Pyrgulopsis, the largest genus of freshwater gastropods (snails and slugs) in North America. Pyrgulopsis species live in fresh and brackish water across the western part of North America; 38 of them are threatened enough to have made it onto the Red List.

Amargosa springsnails, like their cousins, sustain themselves on algae and other microorganisms, as well as any detritus they may find. That detritus has to be pretty small for an Amargosa springsnail to eat it: the species doesn't get much bigger than about a tenth of an inch long, which might be why it wasn't discovered until the 1980s.

Pyrgulopsis amargosae | Photo: Robert Hershler, Proceedings of the Biological Society of Washington, 102(1), 1989

The IUCN's prognosis for the Amargosa springsnail:

In other words: Urban and industrial growth in places like Pahrump, NV is depleting the Amargosa's aquifer, off-road vehicle intrusion into the Amargosa's wetlands (now illegal, but still taking place) destroys habitat, and hikers pose the risk of bringing pathogens and eggs of competing species in the dried mud on their hiking boots. All these issues pose a threat not only to the springsnail but to the other animals that share its habitat, including at least one other native snail and the Saratoga Springs pupfish. Which is why, if you get stranded in southern Death Valley and head for Saratoga Springs with your last burst of energy to drink some of the brackish water there, you're greeted by signs like this:

Saratoga Springs sign, amended | Photo: Ron Gilbert/Flickr/Creative Commons License

Desert wetlands are rare and widely separated pretty much by definition. Aside from birds, bats, flying insects, and large animals that can move from one oasis to another without much trouble, animals that rely on them are thus vulnerable by definition. Tying your future to a wetland in the desert means you're vulnerable to every earthquake that changes water flow, every flash flood that fills your home with silt, and every starry-eyed human booster who decides to drill a well into your aquifer. The Amargosa springsnail is known from just five locations, meaning it may well be just five minor catastrophes away from being wiped off the face of the planet.

That's how extinction works. A species loses a population, just like the Sonoran mud turtle lost its California population: that population is now extinct. If somebody lets a springsnail predator loose in Grimshaw Lake near Tecopa, then the Grimshaw Lake population of Amargosa springsnails might go extinct. We don't tend to get too upset, as a society, when individual populations of species wink out of existence.

But each local extinction means a loss of that bit of genetic diversity, a loss of that cast member in the local ecosystem. The main difference between extinctions like that of California's Sonoran mud turtles and this past week's passing of Lonesome George is that Lonesome George just happened to be the last one in the queue.




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