“Every single living thing is food to at least one living thing.” — Mokokoma Mokhonoana

Every single living thing is connected to other living things. Those connections are through parasitism, predation, herbivory, or pollination, and they are essential for sustenance, growing, and reproducing. Over past millennia, as climates changed and species moved, either previous connections between species were maintained as species shifted together, or new connections were made, or if not, species perished. Our climate is changing once again, and species are moving, trying to stay within their preferred rainfall and temperature regimes, if they can.

Sand dune species have particular challenges with a changing climate. Sand dune surfaces are in motion, requiring species to adapt and evolve to live on a hyper-arid sand that behaves like a fluid. Here lizards and beetles swim both above and below the surface, and plants appear to float above the sand that is seemingly determined to drown them. Leaving the dune is not an option. Sand dune living lizards, beetles, ants, and plants have evolved finely tuned adaptations that suit them well while living on dunes, but which have no value away from the flowing sand. So, as the climate gets still hotter and drier, species here must endure, adapt, or perish. But it’s not just individual species versus climate in isolation. Lizards eat ants and beetles and plants, ants eat seeds and nectar, beetles eat plants (live and dead plants), and plants need their pollinators. One cannot exist without the other, so if any of these connections are decoupled by a changing climate, the whole biotic system could be at risk of collapse. Even at the hottest and driest end of the Coachella Valley sand dunes, so far, after yet another year of record heat and record drought, there are hatchling fringe-toed lizards and flat -tailed horned lizards, still plenty of ants, still beetles, and thanks to late summer rain showers, there are a few seedlings emerging through the sand. So far, nature has prevailed.

Away from the sand dunes, on hillsides and mountain slopes, sand, gravel, rocks, and boulders, make no effort to behave like water. Short of the rare earthquake or flood, they are rock-solid. Compared to sand dunes, stable, rocky ground requires much fewer specialized adaptations. Unlike the isolated, flat sand dunes, these rocky slopes are part of an unfragmented landscape that ranges from near sea level to thousands of feet, well over 10,000’, in elevation. For hillside and mountain species, responding to climate change also could entail enduring and adapting, but it might also include moving to higher, cooler, and wetter elevations. However, moving will only be successful if a species’ connections move with it.

Side-blotched lizards are by far the most abundant lizards occupying those hillsides. These diminutive lizards have evolved a lifestyle strategy that includes breeding often, but typically not living much more than a year, two at most. They currently occur at elevations that range from below sea level to up to 6,000’, a greater range than any other lizard found within the North American deserts. They eat small insects, but in turn they are eaten by a large number of other species. Their predators, and so their connections, include western whiptails, collared lizards, leopard lizards, larger spiny lizards, coachwhips, striped racers, jays, kestrels, and certainly more. So, if in response to hotter conditions, side-blotched lizards shift to higher elevations, many connections will be affected as well.

To be clear, moving to higher elevations is not a conscious choice. It is a matter of greater breeding success at higher elevations creating higher population densities at higher elevations. The questions are, is this species shifting to high elevations, and if so, what is happening to their “connections”? At first blush, changes in the density of side-blotched lizards seems like an appropriate metric. However, density only reflects a response of carrying capacity (responses to food densities), it doesn’t identify the effect on the mechanism. The mechanism is breeding success. Because side-blotched lizards only live about a year on average, in the late summer and fall when breeding has concluded, a stable populations should have a ratio of adults to hatchlings/juveniles of 1:1. A declining population would have a ratio of 1:<1, and a growing population would have summer/fall ratio of 1:>1.

Our community of naturalists’ (Community Science Collaborative) surveys this fall provide some preliminary answers to these questions. Our surveys have covered elevations from 300-5000’.  For those covering elevations from 300-2000’, the side-blotched lizard adult/hatchling-juvenile ratio was 0.35-0.36. At elevations around 3000’ the ratio was 0.62, and at elevations 4000-5000’, the ratio was 1.05-1.06. At the lowest elevations the side-blotched lizard populations are in a steep decline. At around 3000’ the population is still in decline, but at elevations greater than 4000’ the populations are stable and slightly increasing. At those higher elevations the habitat is providing a climate refugia for the side-blotched lizards. Those same areas had higher numbers of side-blotched lizard predators – collared lizards and leopard lizards.

Nullius in verba

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