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black moonscape. Out on the low, low ridges, mineshaft entrances, and other refuges
from the shimmering heat rarely exceed shoulder height, as if we are lumbering giants;
creosote bushes encroach from the surrounding flats, lending flowers and fragrance to
a withering cinderland. Although no dunes interrupt the rubble, sand accumulates with-
in shallow interior pockets, and in them grass blades droop and twirl like drafting com-
passes, their circular tracks enhanced by afternoon shadows. Within an hour of our ar-
rival I'd glimpsed melanistic creatures scuttling over the rocks, as if they too had burst
from some fiery cauldron.
Well-camouflaged reptiles had initially attracted Stebbins, a gifted artist as well
as herpetologist, to Pisgah. In this environment, conspicuous animals are more vul-
nerable to loggerhead shrikes and other predators. Thus black chuckwallas and side-
blotched lizards blend into monochrome territories, the dark-hued flow, while black
desert horned lizards look like lava stones in the sandy patches through which they for-
age. Conversely, tan side-blotched and desert horned lizards inhabit the surrounding
scrub and hardpan where darker ones would be obvious, selection presumably favoring
each version in its respective homeland. The foot-long western shovel-nosed snakes,
however, vary kaleidoscopically, encompassing morphs that elsewhere typify entire re-
gions—gray, salmon, or yellow with black bands, sometimes orange- or black-blotched
within the light hues. Even such small snakes wander more widely than many lizards,
and perhaps here they traverse so many backgrounds that no one version can prevail.
Diversity is higher in this volcanic Shangri-La than elsewhere in California because
typically juxtaposed habitats intermingle, so Pisgah also fueled my interest in ecological
communities. Side-blotched lizards, Great Basin collared lizards, and chuckwallas de-
fend rocky redoubts while desert iguanas, zebratails, long-nosed leopard lizards, desert
horned lizards, and tiger whiptails patrol the flats. Long-tailed brush lizards favor
shrubs and Mohave fringe-toed lizards own the sandy pockets, coexisting such that,
along with secretive western banded geckos and desert night lizards, a dozen species
might compete for food and other resources. Southwestern speckled rattlesnakes and
Baja California lyresnakes prowl ledges above sand-loving western shovel-nosed snakes,
spotted leaf-nosed snakes, glossy snakes, and sidewinders, each of them encountering
generalist western threadsnakes, desert nightsnakes, gopher snakes, long-nosed
snakes, and coachwhips. I never figured out if the occasional desert tortoise was
scratching out a living on the flow or just passing through.
Natural selection was evidently powerful under such harsh circumstances, and
two Berkeley grad students pursued that topic, inspired by our trips to Pisgah and
Stebbins's favorite reptile. Claudia Luke examined the natural history of fringe-toed
lizards globally and showed that their foot specializations arose twenty-six times, in
predictable relationships with habitats. 8 Sand dwellers in Old and New World
deserts—iguanas, geckos, skinks, and so forth—have triangular fringes, whereas water-
running Neotropical basilisks and Asian water dragons independently evolved squarish,
flaplike projections. Meanwhile, John Carothers mimicked a variable population of Mo-
have fringe-toed lizards by clipping the namesake scales off some individuals, then used
a miniature racetrack to prove that on sand they ran slower than unaltered animals. 9
Although Claudia and John hadn't demonstrated ancient differential reproduction—the
actual process of selection—they'd made a strong indirect case for fringed toes as loco-
motor adaptations.
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