"The best scientists are open to the possibility that they may be wrong, and they are willing to change their minds in the face of new evidence." — Richard Feynman

"Science is …. about being willing to ask … questions and follow the evidence wherever it leads." — Neil deGrasse Tyson

What separates science from other approaches aimed at explaining patterns in nature is that the scientific method requires beginning with a hypothesis and then attempting to prove whether it might be wrong before coming to any conclusion of being right. That requirement requires identifying measurements (variables) that can shed light on the veracity of the hypothesis, making predictions based on that hypothesis, and testing (collecting data) to determine whether those predictions are occurring. A standard approach is to create controlled experiments, experiments where just one variable is changed between trials. For instance, if the question is whether a plant or lizard is sensitive to increases in temperature, a scientist could rear their organisms in a climate-controlled laboratory, with half the individuals kept at an expected preferred temperature and the other half reared in a series of chambers along a warming temperature gradient. Other possible variables, genetics (all test subjects typically have a homogeneous genome), soil, nutrients, lighting, and a lack of interaction with other species, are all kept constant. At the end of the experiment characteristics between the groups are measured, maybe growth rate, seed production, or maybe stress hormones, to see if there are differences. If there are differences you can accept the hypothesis that your species is sensitive to the temperature levels you tested; if no differences are found, then at least at the temperatures you tested, no sensitivity exhibited. Simple, but maybe not as effective at explaining patterns in nature as it might seem.

The problem is that those experiments in climate-controlled laboratories are not proxies for what those species experience in nature. As the botanist and conservation biologist Frank Egler once stated: “Nature is not more complicated than you think, it is more complicated than you CAN think.” Individuals within a natural population are genetically diverse and so respond to their environment as individuals not as carbon-copy replicates. They are subjected to year-to-year differences in predation, parasites, competitors, feast and famine, cold and hot temperature fluctuations, droughts, floods, and perhaps countless other variables that might influence growth, stress hormones, and ultimately population increases or declines. Lizards might adjust their activity times to avoid stressful temperatures. They also exist in diverse landscapes where large boulders might act as thermal buffers, moderating the temperature for those organisms living within rock crevices or nearby. Or they may take advantage of differential water availability due to earthquake faults, or rainfall streaming over the aforementioned boulders, creating higher moisture availability that might then allow for higher temperature tolerances than elsewhere across this hypothetical landscape. Nature is not a controlled laboratory, its messy. Controlled laboratory experiments can provide insights regarding physiological thermal responses, but not necessarily how those tolerances translate into what we see in nature. Given that reality, can we do meaningful science that would inform us as to whether the environmental change humans have catalyzed is impacting nature?

The answer is yes. An alternative approach is to document what is happening in nature over enough time and across enough different locations to see if there are consistent patterns that emerge. If a warming planet is affecting the distribution of our desert species, then on those sites that are warmest and driest (lower elevations), that change should be most pronounced. In contrast, changes at higher elevations with cooler temperatures and often higher precipitation levels should be less if at all. However, the complexity inherent in nature potentially confounds any clear conclusions.  To minimize that problem, we select sites (trail surveys) that are similar in most respects, for instance upland habitats away from wetter areas such as washes with occasional water flow and permanent wetlands. We have found that areas that have higher levels of permanent or seasonal water appear to act as climate refugia, areas that buffer against the impacts of increased temperatures. These are important sites to identify, but they muddy any between site comparisons of upland habitats. So, to the extent possible, we stick to upland habitats so that the site comparisons are closer to an apples-to-apples evaluation.

The time element means that this approach is not something that can be readily concluded within the tenure of a graduate student’s university career. It is, however, something a dedicated team of volunteer community scientists can do, and we have shown that they are doing it very well. Using the long-term weather records collected at the Indio Fire Station, from 1906 through 1985 the average annual temperature was a consistent 73˚ F. From 1986-1995, the annual average increased to 75˚ F. From 1996-2019 it increased again to almost 77˚ F, and from 2020 to 2023 the average is now 77.6. There is no question that it has become warmer, and there is no indication that trajectory is changing anytime soon.

In our case, we are asking the question of whether a warming planet is changing the distribution of native plants and animals, potentially putting some at risk of no longer being able to exist here at all. So far, the data in hand supports our predictions that on the warmest-driest sites lizard populations are shifting to higher elevations. This does not mean that individual lizards are actively traveling to higher elevations. Rather it indicates that those lizards already occurring at those higher elevations are likely reproducing with higher success than those at lower elevations. These findings apply to side-blotched lizards, small, sometimes abundant, but short-lived insectivores, and for chuckwallas, large-bodied vegetarians. The ability to track preferred climate conditions as those conditions retreat from the lowest elevations and extend to higher elevations is a means for these species to adapt and survive in a changing world. The alternative is extinction.  

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.