“As the cold came on, and each of the more southern zones became fitted for arctic beings and ill-fitted for their former more temperate inhabitants, the later would be supplanted and the arctic species would take their places…. As warmth returned, the arctic forms would retreat northward, closely followed up in their retreat by species of the more temperate regions.” – Charles Darwin, On the Origin of Species

By DR. CAMERON BARROWS

Here Darwin described how species responded to changing climates, an idea that was revolutionary during his time when species were then thought to be stable, staying the same both in form and place, back in time and into the future. Then the idea that species could go extinct was being hotly debated, even as fossils representing animals no one had ever seen alive were being unearthed. Those on the species-stability side of the debate assured the others that somewhere, someday explorers would find a thriving population of living woolly mammoths. Thomas Jefferson, then the third U.S. President, sent Meriwether Lewis and William Clark on a continental-wide journey to find a navigable river to the Pacific Ocean to foster exploration and colonization, to record the indigenous people they encountered, and to find some mammoths. They failed to find mammoths or the navigable river. But they did, thanks in no small part to their indigenous guide, Sacagawea, encounter many indigenous tribes and were able to glimpse their pre-European-contact lives and culture. They also provided a first-time detailed account of the biological richness of North America, yet to be colonized by European settlers.

Today we are all too aware that animals and plants can and do go extinct. We also know that there have been at least five major, worldwide extinction events, events in which 75-95% of Earth’s life was extinguished, and then, over time, new forms evolved. 

The most recent mass extinction occurred 65 million years ago when an asteroid slammed into the Earth, and most dinosaurs disappeared. Only the smaller, feathered dinosaurs survived; today we call them birds. The extinction of larger carnivorous dinosaurs opened the door for mammals to move out of the shadows and beyond their burrows to radiate into the myriad of forms, including ourselves, that we see today. Although there were different causes for each of the five extinction events, in all cases there was believed to be a relatively rapid climate shift. This has left some to speculate that with our current climate changing trajectory, perhaps we are on the precipice of yet another worldwide extinction event.

The previous climate changes Darwin referred to were the result of our planet shifting and tilting its orbit either closer to or away from the sun. Today we are facing a new changing climate, departing from the climate which we and other species have experienced for roughly the past 15-20 thousand years. Except this time there is no shift or tilt in our orbit. This time it is the result of our success at harnessing and employing fossil fuels for transportation, electrical energy, food and industrial production, resulting in increasing the amount of carbon dioxide and methane in the Earth’s atmosphere. This time the climate is changing faster, and we have created barriers to species movements in the form of cities, freeways, and agriculture, landscapes that species cannot easily negotiate. For our desert adapted plants and animals, modeled climate scenarios have shown that for them to stay within their current preferred climate “window” they will likely need to shift incrementally up into our desert sky-island mountains. Another alternative is that they adapt to the increasingly warmer and drier climate. In other words,  move upslope, adapt (evolve) new tolerances, or face extinction. With the rate of climate change we have seen to date we won’t have too long to wait to see which alternative occurs.

Collecting the data that will let us know if animals and plants are moving upslope, adapting in place, or slowly going extinct is ideally suited to volunteer community scientists. The reasons are several. First, to come up with clear answers will take many years, even decades. Academic scientists, with their publish-or-perish pressures, do not have the luxury of taking that long to come up with answers. Second, the answer will emerge only after collecting data across many locations to ensure the results represent general patterns, not idiosyncratic, site-specific responses. Academic scientists and their students don’t have the decade-long time and funding to devote, no matter how important the answer is. Community scientists don’t have these time and funding constraints.

Our results so far illustrate the inherent complexities of trying to answer these questions. What we have seen is that during prolonged drought, at lower elevations there is increased shrub mortality and lower lizard population sizes compared to conditions at higher elevations. But then a tropical storm happens followed by a monsoon, or then El Niño conditions result in a wetter year. Then there are new shrub seedlings and hatchling lizards everywhere. If warmer temperatures, both over the desert and in the ocean, catalyze stronger monsoons and more tropical storms, maybe on average species will not need to move or adapt to drier world because those periodic wetter conditions will act as “rescue events”, and so on average maintaining the status quo.

Our multiple site approach should help sort out these complexities. The eastern locations tend to get more of the monsoon influence, whereas the western and northern sites get more of the El Niño effect. That should allow us to parse out the relative impacts of summer versus winter precipitation. One early result is that winter rain tends to germinate more non-native, invasive annual plants compared to sites that get mostly summer rain. Perhaps more winter rain, with more weeds, is less of a rescue event than summer rains with less weeds. If so, then the lizards and their food plants should be more stable on the more eastern sites. Thanks to the efforts of our community scientists, we will be able to answer this question.

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