“The greatest threat to our planet is the belief that someone else will save it.” — Robert Swan

By CAMERON BARROWS

Dramatic climate shifts in the past, most recently during the Pleistocene, catalyzed ecological changes, including extinctions. Without those extinctions we would currently be sharing North America with mammoths, mastodons, dire wolves, and dozens of other “charismatic” species known to us today only as fossils. Those extinctions dominate our perceptions of what climate change can do, but do not forget every single species alive today survived those climate shifts. Understanding how those who survived and eventually thrived can provide clues to how species can survive our current climate path.

Desert regions are becoming both warmer and more arid, potentially challenging the ability of even arid-adapted species to exist within their current ranges. Faced with a still warmer and increasingly arid environment, desert plants and animals face an uncertain future for which they must either endure these new climate extremes, evolve tolerances to changing conditions, track their preferred climate by shifting their distributions, or perish. Many animal species worldwide are shifting their ranges to higher elevations including many desert lizards. Native plants across the lower elevations of the Colorado Desert of southern California are shifting their ranges to higher elevations. To be clear, individuals within a population are not moving to track their preferred environment. Rather, where there is insufficient recruitment to sustain their populations at their more arid, typically lower elevation habitats versus positive recruitment at less arid, cooler, higher elevation habitats, the population incrementally shifts to higher elevations. These upslope shifts underscore the importance of desert “sky islands,” mountains surrounded by lower, hotter, and drier desert habitats that provide a “stairway” to cooler-wetter habitats at those higher elevations.

Of the survival options, endure, evolve tolerances to new climates, or shift distributions, shifting seems to be one of the most common strategies. However, shifting upslope may have its challenges as well. Animals and plants adapted to hot, arid climates must either be able to tolerate hot temperatures or be able to avoid those temperature extremes. For plants, avoiding hot dry conditions might entail having drought deciduous leaves (dropping leaves during the summer), or in some cases having no leaves at all (such as cacti). Shifting to higher elevations may mean these plants are able to stay within their existing summer climate tolerances, but winter temperature may still be colder, with leaf-killing frosts still possible. Climate change not only means warmer conditions, but it also includes more variable, extreme weather. If a plant puts on leaves and flowers in the early spring at lower elevations, frosts could kill those leaves and flowers at higher elevations. Thick spongy stems (cacti) could be particularly vulnerable to frosts or extended periods of being blanketed by snow. Or, if the plant can tolerate those occasional bouts of extreme cold, will its essential insect pollinators be able to handle the cold?

Among reptiles, side-blotched lizards have one of the largest ranges, extending throughout each of North America’s warm deserts and well into the colder Great Basin Desert. As such, they have been survivors, sustaining populations despite all nature has thrown at them. Still, with the extreme aridity of the past couple of decades, their populations are becoming increasingly sparse and fragmented in those areas where drought has been most extreme. At the same time, we are seeing side-blotched lizards shifting to higher elevations. As with desert-adapted plants, an important question is whether chilly winter weather will “cap” the ability of these lizards to continue to move up mountains. Unlike most lizards that brumate (going into an extended period of slowed metabolic inactivity) during the cool temperatures of winter, warm desert side-blotched lizards do not brumate and so are active every winter day. Their small size allows them to warm rapidly and then take advantage of winter-active insects.

The winter of 2023 has been a “throwback” to winters of decades ago, colder and with more snow capping our desert mountains than has been seen for the nearly 40 years I have lived here. Before then, deep frosts were expected each winter even across the desert floor. Snow covered the Santa Rosa Mountains all winter long, unlike the occasional light dusting that has become the norm in recent years. But there was so much snow this year that the upper-expanding elevation edge of the side-blotched lizard range was snow-covered all winter. What became of side-blotched lizards, and all lizard species, along that upper expanding edge of their range? Based on our surveys so far this spring, the lizards, wildflowers, and pollinators are all doing well. Even during surveys conducted when temperatures barely broke the 60s, the lizards of all species were out sunning themselves on boulders. If there is a winter cold temperature “cap” or blankets of snow that might prevent incremental shifts into suitable habitat, side-blotched lizards have not reached it yet.