“A million years is a short time - the shortest worth messing with for most problems. You begin tuning your mind to a time scale that is the planet's time scale. For me, it is almost unconscious now and is a kind of companionship with the earth.” ― John McPhee

By DR. CAMERON BARROWS

Perhaps when we consider rocks, anything less than a million years is a mere eye blink, but when we consider life, the creatures we see around us today and the ones that were here before them, then thinking in thousands or even hundreds of years can be significant. Just 20,000 years ago the desert around us was a very different place. Mammoths, mastodons, ground sloths, camels, dire wolves, saber-toothed cats, bison, and cheetahs all roamed what we now call the Mojave and Colorado Desert, including the Coachella Valley. Our earth was nearing the end of an “ice age” and there were signs of warming, but ice sheets still covered Canada and the northern tier states of the U.S. No permanent ice this far south, and at these latitudes it wasn’t that the low temperatures were colder, but the high temperatures were much cooler. And it was wetter. North of here it was colder still; animals and plants that had moved north before the most recent ice age neared its peak, 50,000 years ago, had again been pushed south in search of a milder climate, and they found it here.

Ice ages can be particularly tough on reptiles, and especially lizards, a group that depends on warm sunny days to warm their bodies to be able to move fast enough to avoid predators, and to warm their core to be able to digest their food. Even today, lizards barely extend more than a hundred miles or so into Canada. It’s just too cold too much of the year. One of those lizards whose range almost reaches Canada is the common or northern sagebrush lizard, Sceloporus graciosus. The most northern of common sagebrush lizards exist within a mere hundred miles of Canada in the states of Washington, Montana, and North Dakota. Their southern limits extend down the Sierra Nevada Range in California, the Colorado Plateau, and across the Great Basin Desert. They are absent from North America’s warm deserts; apparently tolerating cooler climates has left them intolerant of very warm climates. But, during the coldest periods of the ice ages common sagebrush lizards were pushed south, at least as far south as northern Baja California to southern New Mexico and Texas. Here across these southern latitudes the sagebrush lizards found refuge from the biting cold in the north during the depths of the ice ages. This pattern was repeated by lodgepole pines, limber pines, Douglas fir, mountain mahogany, Great Basin sagebrush, and countless other plants and animals.

Eventually the earth’s orbit and tilt shifted again, bringing our northern hemisphere closer to the sun once again. Close enough to melt the ice sheets covering Canada and Alaska, and warm enough to allow the warm deserts to occupy the spaces we know today. For those species that liked cooler climates and had found refuge from the ice ages’ severe cold in the southern latitudes, there were four options. Follow their preferred climates as they shifted back north, climb up into the cooler “sky island” mountains that were otherwise surrounded by warming deserts, physiologically adapt to warmer climates, or go extinct. We know what happened to the mammoths, mastodons, ground sloths, camels, dire wolves, and saber-toothed cats. The sagebrush lizards followed three options. Many incrementally shifted north to their current distribution. They accomplished this not by migrating north, but through differential reproductive success; they produced more offspring along the northern portions of their refugia in the south (and conversely less in the southern latitudes), incrementally shifting their population north. Rather than shift north, one portion of their population adapted to warmer climates, sand dune habitats in southeastern New Mexico and southwestern Texas, along the northern edge of the Chihuahua Desert. This population became isolated from their brethren as their cousins shifted north. Through that isolation and adaptation to both warmer conditions and life on sand dunes, these lizards eventually became a separate species, Sceloporus arenicolus, the dunes sagebrush lizard. This species was just recently listed as endangered by the U.S. Fish and Wildlife Service, largely due to habitat alteration resulting from oil well construction throughout their remaining habitat.

A third option was taken by sagebrush lizards occupying habitats adjacent to sky islands. As with better reproductive success in the northern latitudes, they also had better reproductive success as they moved to higher elevations in the sky island mountains. Eventually, as with the dunes sagebrush lizard, these mountain populations became genetically isolated from their northern cousins. Thousands of years of isolation, and adaptations for living in the mountain forests (rather than sagebrush steppe habitat of the Great Basin Desert) eventually resulted in they too evolving to be a different species, Sceloporus vandenburgianus, the southern sagebrush lizard. The name vandenburgianus commemorated the lifelong work of naturalist and herpetologist, John Van Denburgh (1872-1924). Among Van Denburgh’s accomplishments was recreating the California Academy of Science’s herpetology collections that were destroyed during the San Francisco earthquake (1906).

As our climate continued to warm as it left the last ice age behind, and now is warming again due to the highest levels of carbon dioxide in our atmosphere recorded in the past hundreds of thousands of years, southern sagebrush lizards may be shifting to still higher elevations. As of now there are isolated populations in the Big Bear region of the San Bernardino Mountains, on the slopes of Mount San Jacinto, the Santa Rosa Mountains, and the Sierra San Pedro Martir in Baja California, Mexico. These are the lizards that greet you as you disembark from the Palm Springs Tramway at 8,600 feet and walk down the path to Long Valley. In between these taller mountains there are a few small populations, hanging on by occupying cooler north-facing slopes, deep, moist canyons, and beneath the canopies of dense black oak, fir, and pine forests. Otherwise at elevations below about 6,000 feet they are few and far between.

The increasing levels of isolation between the southern sagebrush lizard populations on those aforementioned +8,000 feet high mountains beg the question as to whether their genetics are shifting, rendering them now or in the future as separate subspecies, or even full species. No one has yet endeavored to measure the genetic differences between these isolated populations. However, as genetic analyses are becoming increasingly less expensive and more precise, eventually someone will take this on as their graduate research. In doing so, they just might be able to glimpse the process of how and at what speed new species are forming.

Nullius in verba – Go outside, tip your hat to a chuckwalla (and a cactus), and think like a mountain