The summer-like temperatures this week have meant that our lizard surveys have shifted more to the western (slightly cooler) portions of the Coachella Valley floor, and earlier starts, but the lizards have still been plentiful.
I first wanted to draw your attention to the attached photo (UMIN_3) and to the "bling" the lizard is sporting. One group of our plots is adjacent to a single, long-term plot that has been surveyed by the Boyd Deep Canyon Desert Research Station
scientists (a UC research station south of Palm Desert) since the early 1980s. Al Muth, Mark Fisher, and now Chris Tracy have made an effort to survey their plot twice a week from March through October for the past +35 years, counting and marking every fringe-toed lizard they find. Rather than trying to catch the same lizards every survey, they have attached a unique set of colored beads to each lizard so that they can identify them without further harassing them. I'm often asked whether attaching the beads is harmful to the lizards, and I answer by looking into the audience at those with pierced ears and asking them. The large male shown in UMIN_3, or as they would know him as "gold-white-orange, or #1905", wandered off their plot and on to ours. According to Mark Fisher, this male was hatched in the Fall of 2017, was marked on their plot in 2018, and was last seen in the Fall of 2019. Apparently he got an itch to discover what was on the other side of the dune, and found himself on one of our plots.
The reason I bring this up is to celebrate the value of long-term studies. Their plot is a bit over 2 hectares, or about 5-6 acres. Early in the 1980s they found over 300 fringe-toed lizards occupying their plot. Over the years, with fluctuations in sand movement on and off their plot, droughts and wet years, and perhaps even ground water levels, the numbers of lizards have changed every year, sometimes dropping to as few as a dozen or less, but then rebounding into the hundreds a few years later. The take home message here is that natural populations fluctuate naturally, including some "order of magnitude" changes. The challenge to knowing why and whether we can or should intervene. Shallow sand depths, drought and low groundwater levels are not good for lizards, and when occasionally they all coincide, the lizard population crashes. Deep sands, wetter conditions and healthy shrubs are all good for lizards, and when they coincide the lizard numbers swell. It makes sense, but we would never know how important each of these elements are without long-term studies.
Our own surveys have been occurring for a mere 18 years. Rather than focus on the year to year changes on a single plot, we also wanted to understand the changes across what is left of the entire range of this species and have added the effects of climate change, habitat fragmentation, and invasive weeds to rainfall and sand depth to the factors that impact the lizards. We survey 78, 0.1 ha plots, and so attaching bling to each lizard is out of the question. Rather we use the tracking method I've described before. The scale is different between the two approaches, but we find that the best habitat without weeds, loose sand, and with adequate rainfall will support up to 10-15 fringe-toeds per plot while with poorer conditions there can be as
few as one or even less; doing a bit of math reveals that each survey method came to the same conclusion regarding the magnitude of year to year fluctuations. From these long-term studies we can provide real guidance when asked how important maintaining sand sources are, or whether weed control is worth the effort and costs. Despite being a bit weedy this year, This is shaping up to be a good lizard year - as evidenced by the lovely lass shown in UMIN_1 & UMIN_2,
being gravid (notice the red hues on her sides and tail on UMIN_2). Just about every adult female fringe-toed we've seen this spring has been gravid. Still, in weed-free areas the lizards are doing the best, while in weed-choked areas they are doing poorly.
Long-term studies are essential to understanding the complexities of nature. Unfortunately they are increasingly rare and rarely unsupported by funding agencies. The work you naturalists do is in many ways filling that need, both by helping us on our surveys, and by initiating your own long-term efforts. Thank you!
Finally, I wanted to get back to the question I left you with last week regarding the reason that female leopard lizards are so much larger than the males. I received several excellent answers. Tracy Albrecht pointed out that small males can be very attractive to some females (citing Tom Cruise and Davy Jones [lead singer for the 1960s band "the Monkeys"]). Tracy and Robert Ross also pointed out the possibility that, by their different sizes, leopard lizards may be eating different prey, and so avoid competing with each other. And then Peter Schwartz came up with an idea that I had also been developing, that like spiders and praying mantises, females avoid being eaten by males by being so much larger than the males. Of course they then eat the males. In "Lizards of the American Southwest" Brad Hollingsworth wrote that leopard lizards are noted for eating other lizards, including lizards nearly as large as they are, and including other leopard lizards. So for those reproductively critical females to avoid being prey, they need to be larger than the males. Of course evolution doesn't need to be limited to just one factor, in fact the more advantages a change or difference might provide, the more likely evolution will shift a species toward that direction. Thank you all for those excellent responses.