“I want to realize brotherhood or identity not merely with the beings called human, but I want to realize identity with all life, even with such beings as crawl on earth.” — Mahatma Gandhi

"Nature, red in tooth and claw." — Alfred, Lord Tennyson

Change in nature is sometimes imagined as competition between species, winners and losers, “nature red in tooth and claw." 

There is some of that, the best examples being the introduction of invasive species. Successful invasive species win the competition for space and for water. Sahara mustard and tamarisk produce more seeds and grow faster than the native plant species, and so crowd the natives out, sometimes eliminating them altogether.  Then, what follows has been termed the “domino effect” or a “trophic cascade," pollinators and herbivores that were adapted to using the native plant species may find nothing of value in those new interlopers, and so their populations decline in step with the loss of native plants. The falling dominos then extend throughout the food web.

Without a newly arrived species upsetting the status quo, nature red in tooth and claw may not be the primary catalyst of change. There are ebbs and flows of one species or another, but rarely does one eliminate another, even more rarely is there a trophic cascade. 

Then there is change that is typically catalyzed by something at a scale much larger than a turf war between species. Think climate change, either resulting from natural orbital shifts, or, as in the current warming, as a result of human activities. When conditions to which species have adapted to rapidly shift to something hotter or colder, drier or wetter, those fine-tuned adaptations no longer serve those species well. By comparing historical records dating back a century or more from naturalists such as Joseph Grinnell and others, today scientists have identified substantial declines in the abundance and species richness of Mojave Desert birds. On the average they found a 43% loss in bird species richness at sites across the Mojave. Declines were greatest on drier sites, less so where perennial water was still present. Only one native bird species appeared to be more abundant — ravens. Ravens have been the beneficiaries of human garbage and road-killed mammals and reptiles. 

Are those findings for desert birds paralleled by declines in reptiles and mammals? Certainly, desert tortoise populations are far less abundant than back in Grinnell’s day. The reasons for their decline include climate change, but also involve habitat fragmentation by roads and associated road mortality, and those ravens. Some ravens have learned to specialize on eating baby tortoises.  For other reptile species the changes that have occurred so far appear to have been more subtle. It seems that being exposed to the sun and heat 24/7 (birds) has disadvantages compared to species who hide in burrows and rock fissures when temperatures and overall conditions (aridity) are less than optimal. The one advantage birds have is their mobility. When conditions get bad, they fly elsewhere – unless the conditions are bad everywhere. Dr. Lori Hargrove and I overlapped in time as PhD students at UC Riverside. She was and is a bird biologist, focusing on studying desert birds. Perhaps the quintessential desert bird is the black-throated sparrow, and Lori focused much of her research on that species. What she found was that the sparrows moved around depending on aridity. In wet years they nested at lower elevations, in dry years at higher elevations, or not at all.

Reptiles typically do not have that kind of mobility. What they do have is the ability to “shelter in place” to survive “bad” years.  That ability to shelter in place is often a function of their size; smaller species such as the seemingly ubiquitous side-blotched lizards can shelter for days or weeks, but they are short-lived, usually individuals not surviving more than 1-2 years, so to survive as a species they must breed every year.  Larger species such as chuckwallas, desert iguanas or collared lizards live for a decade or maybe even two decades. Breeding every year is not essential, and so they can shelter for a year or two or more to wait for better conditions. Between 2012 and 2016 it was dry, really dry, here in the Coachella Valley, with very few new green plants for vegetarian lizards such as desert iguanas to eat. We survey the lizard populations on the dune remnants every year, and the iguanas disappeared from almost every site that lacked palatable deep rooted perennial shrubs, such as indigo bush, during that drought. Then, in 2017 it was a wet year with plenty of green plants and flowers, and the iguanas returned. They never left, they just sheltered down in their burrows until better forage was available.

What we are seeing with the side-blotched lizards is that their populations are shifting to higher elevations where they can find dependably better conditions. They still occur at the lowest elevations but compared to middle and higher elevations their numbers are very low. What we are seeing now is an incremental shift up the mountains. On two separate trails near the Idyllwild region in the San Jacinto Mountains we have conducting annual surveys every year since 2013. At the beginning we found the highest side-blotched lizards at elevations of 1600-1700 m. Last year in 2020 the highest side-blotched lizards were at 1800-1900 m. To be clear, the individual lizards are not climbing up the mountain; what is happening is that their breeding success is higher at higher elevations, and dispersing hatchlings are allowing this lizard year be year “inch” up the slope. It is not nature red in tooth in claw that allowed these lizards to move, it is simply differential breeding success — better at middle and higher elevations, less so at the lowest elevations.

We are also seeing a similar upslope climb in desert horned lizards. Horned lizards eat ants and ants are good at surviving, even during dry periods. However, ants, and so horned lizards, still do better with more dependable conditions at middle to higher elevations.  It is not a totally fair comparison (small sample size) but take a look at the condition of a desert horned lizard Cathy Wiley found in the Indio Hills (390 m) versus one I found at 700 m on the Art Smith trail, both last week.  Sometimes pictures speak volumes.

Moving upslope through differential recruitment at the higher ends of species’ ranges is a strategy many of our lizards are employing. But what about the dune lizards? There are no dunes up in the mountains, so the dune lizards have nowhere to go. It is wetter and cooler on the dunes at the western end of the valley. And dune sand holds on to rainwater better than do alluvial sands. The question then is whether that will be enough for them to sustain populations until we get climate change stabilized and reversed?  

Nullius in verba

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