- Author: Cameron Barrows
A "Natural History Note" From UC California Naturalist's lead scientist, Dr. Cameron Barrows.
In nature, species are constantly “striving” to be “better” species. To be clear, this is not a conscious effort, rather that improvement can occur through reproduction, there are new combinations of genes being created with every generation, both through mutations and through the mixing of genes through sexual reproduction. For asexual species, gene mutations are the avenue for change; for species capable of sexual reproduction, there is both mutation and the unique gene combinations of the two parents. Change (evolution) for asexual species is slow. Change for sexual species is much faster. The arbiter of whether a mutation and/or a unique gene combination is “better”, more successful at surviving and ultimately reproducing themselves, is the environment, and the environment is always changing. Slowly or quickly, change is happening. Now, through climate change and the introduction of invasive species, we are often the catalysts of change. Before we arrived on the scene climates still changed (but more slowly), and new species did show up and disrupt the status quo, and once in a great while an asteroid slammed into the earth. Change has always been a feature of nature, and the species that make up the nature we all love are there because they were “better” than their predecessors at surviving and reproducing in today's environment. Tomorrow's environments will be different.
Creosote bush is successful by any measure. They have become one of, if not the, most numerous species in each of the Chihuahua, Sonora, and Mojave Deserts. I can think of a handful of plant species that straddle two of those deserts, but only Creosote bushes thrive in all three. Over the eons they have evolved, via mutation and unique gene combination, a cocktail of chemicals in their tissues that repel over-browsing by rabbits and pronghorn antelope and tortoises and desert iguanas and chuckwallas. That same cocktail appears to repel damaging bacteria and possibly viruses, and so has the potential to benefit human health as our disease vectors develop immunities to the antibiotics we use today. But you might object, what about the 60 or so insects that are specifically associated with creosote bushes, what about the 14 species of creosote gall midges that lay their eggs in the plant's tissue to create abnormal growths for their larvae to eat and be protected from parasites? The answer is that none of those pesky bugs kills or reduces the reproductive potential of their creosote bush hosts. That which does not kill them makes them stronger.
The creosote bush's strategy is longevity. They can live for hundreds and in some cases thousands of years, in part because nothing eats them (enough) to kill them. During their long lives there will be many droughts and many wetter periods. Only occasionally will the conditions be right for long enough to allow for successful reproduction. “Young” creosote bushes are rare compared to the densities of their parents. If you live for centuries you do not have to be successful at reproduction very often, and the cost of producing flowers, fruits, and seeds almost every year is not enough to subtract from their longevity. So far, in our analyses of how species are responding to the levels of climate change we are currently experiencing, creosote bushes seem to be shrugging their leafy shoulders.
If longevity is good, then perhaps desert tortoises are also adapted to surviving climate change. Desert tortoises do not live centuries, but they might live as long as we humans do, which is much longer than most wildlife species. Through their lives they too will experience droughts and wetter periods. Like creosote bushes, there are increasingly rare combinations of wet years that foster survivorship in the vulnerable hatchling tortoises. Not being able to predict the future any better than we can, except for in the driest years, female tortoises will lay a clutch of eggs in most years, hedging their bets that the eggs will hatch into a wet weather cycle. If it is a wet spring with lots of food, the females may lay larger clutches and sometimes multiple clutches, all depending on the health and condition of the females. Unlike creosote bushes, there is a considerable cost to the female tortoises for each clutch they lay. If conditions are dry and there is little or nothing for the tortoises to eat for multiple years, there can be a terrible cost in terms of the females' body condition, health, and survivorship. Dr. Jefferey Lovich has been studying desert tortoises for decades. In recent years he has found high tortoise mortality in some populations, and when examining the dead tortoise shells, he has found that the vast majority of dead tortoises were females. Those areas with high female mortality have been hit particularly hard by increasing aridity born by modern climate change.
At the opposite end of the longevity spectrum are side-blotched lizards, which typically live for one, or more rarely two years, especially in our hot deserts. Dry year or wet, they need to breed and produce viable young within a year, or at most two years, or their population is kaput. What we are finding is that this lizard's preferred habitat, as evidenced by where we find them at the highest densities, is shifting to higher elevations. There are still some at lower elevations, but those are usually in or near desert washes where rainwater can be concentrated, and so conditions are not quite as arid as those in the open desert. Or they occur in appropriately landscaped suburban yards where conditions are also less arid (if cats or the high concentration of roadrunners do not eat them). Otherwise, side-blotched lizard populations are moving up in elevation. Those living at higher elevations reproduce better than those at the lower elevations, so that upper elevation edge is expanding while the lowest elevation edge is incrementally contracting. In dry years that shift is clear; in wetter years there is a bit of a reprieve and the lower edge lizards do ok. Every year is different, but the overall trend is pushing these lizards, along with other species, up in elevation.
Long-term observations are essential to discover these patterns. A community of naturalists that help collect these data at multiple locations across gradients of aridity, are equally essential.
Nullius in verba
Go outside, tip your hat to a chuckwalla (and a cactus), and be safe.
- Author: Cameron Barrows
Biodiversity can be appreciated at multiple scales, from within a species and within populations (at a genetic level), to scales that encompass communities of a variety of species within a habitat or across landscapes of many habitats comprised of interacting communities of organisms. For most of us there is an understanding that higher biodiversity at each of these scales is a positive attribute, but why?
In part the answer is that with greater biodiversity there comes higher levels of redundancy. Communities with lower biodiversity are more fragile than those with higher biodiversity. Imagine a habitat with a single species of plant-eating insect and a single species of an insect-eating lizard. As long as there are just enough insects to sustain a healthy population of lizards, the there is a level of equilibrium. But, if a severe drought, or if a pandemic kills the insect, the lizard population starves. Or if a lizard-eating bird enters the community and reduces the lizard population, the insect population could increase to a level where the plant community is damaged by the insects and their voracious appetites. Either way the community collapses. However, if that community included multiple species of insects, and multiple species of lizards, that redundancy can buffer the community. The role of any one species can be filled by another and the dynamic equilibrium between predators, prey, and vegetation can be sustained.
James Estes studied a marine environment in the Aleutian archipelago that lacked biodiversity. There was a single predator species (sea otters), very few prey species (mostly sea urchins), and a single plant species (giant kelp). Sea otters ate the urchins, and the urchins ate the kelp. As long as the numbers of each were in balance (equilibrium) a dense kelp forest existed that acted as a nursery for a multitude of fish species. But then the local Orcas developed a taste for sea otter, decimating local otter populations. Without otters the urchin population exploded, and they ate all the kelp. There was no redundancy to compensate for the decline in otters; the community collapsed, and the critical fish nursery was lost.
Kevin Crooks studied coastal sage communities near San Diego. Coastal sage is generally a diverse community of plants, insects, lizards, songbirds, small seed and plant eating mammals (rodents), medium-sized omnivorous mammals and a few large predatory mammals (mountain lions, bobcats and coyotes). However, San Diego is a popular place for people to live, and the coastal sage community has been sacrificed for thousands of new homes to meet the needs of a burgeoning population of humans. Soon the coastal sage community was sliced and diced until there were just a few isolated natural habitat fragments left. Kevin's question was whether those habitat islands still retained the biodiversity of what once characterized this community. The first to go were the large predators; the big cats and the coyotes could not maintain populations in such small habitats. Then something curious happened. Without the larger predators around, the medium sized (meso-predators) mammal populations (skunks, raccoons, weasels, and opossums) exploded, and preyed upon the lizards, songbirds and small mammals to the point where the smaller creatures were no longer able to maintain populations. Excluding the top predators resulted in a “trophic cascade” and a loss of biodiversity.
Then there is genetic biodiversity at a species or population level. Darwin worried about this for his own family, even before there was a modern understanding of how genetics works. At that time, and for centuries before, European culture dictated that marriages occur within social classes and typically within a finite group of families with social and economic ties. Royal families throughout Europe intermarried to solidify strategic alliances. The result was an inordinate propensity of hemophilia and insanity. The Darwin and Wedgewood (famous for their fine china) families had similar ties of intermarriage. Darwin married his first cousin Emma Wedgewood. Darwin himself suffered in his middle and older ages from undiagnosed debilitating gastrointestinal distress that was shared by several of his cousins. Emma and Charles had ten children, seven of which survived to adulthood. Just three of his adult children had children of their own. Darwin and Emma had a long happy marriage full of love and respect, but he was guilt-ridden that their lack of genetic diversity had doomed their children, despite the fact that three of his sons were Knighted for their respective advancements in botany, astronomy and engineering. Had the Darwin-Wedgwood intermarriages continued Darwin's guilt would have likely been well-founded and his lineage may have had a short family tree. Perhaps because of his concerns, his children and grandchildren and great-great grandchildren found spouses outside of that close family circle, and there are now some 100 descendants of Charles Darwin. Today one of those great-great grandchildren, Sarah Darwin is a professor and botanist who has studied rare plants in the Galapagos Islands. Another, Christopher Darwin lives in Australia and works on his goal of halting the global mass extinction of species, and a third, Jos Barlow is a noted ecologist. Charles would be pleased.
I saw another example of the effects of genetic diversity on our community science climate change-effects survey yesterday. We were on the Boo Hoff trail, at the driest end of our survey gradient. What struck us all as curious was that of the ocotillo that dotted the hillsides along the trail, a few were leafing out, while most were still dormant. Ocotillo have adapted to dry desert conditions by leafing out after significant rainfall events, and if there is additional sufficient rain, flowering, fruiting and then dropping all their leaves and going dormant until the next rain happens. Under the right sequence of rain events they can repeat this sequence up to three times in a single year. While we did have a brief and scant rain shower about two weeks prior to our survey, most of the ocotillo were unconvinced that it was enough to risk putting precious resources into forming new leaves. But a few were convinced. Those were the risk takers, “betting” that more rain would come, and by getting a head start they would stand a better chance of completing their flowering and fruiting cycle before drought once again pushes all the ocotillo back into dormancy. If they are right, they will produce more seeds and have more potential to continue their genetic lineage. If they are wrong, they will have wasted those precious resources, and if the ensuing drought is particularly long, and hot they may not survive to reproduce again. Genetic diversity producing risk takers and conservative wait and see-ers. In an unpredictable desert climate one or the other, or both will win the survive and reproduce lottery.
Biodiversity at all scales is good.
- Author: Cameron Barrows
A "Natural History Note" From UC California Naturalist's new lead scientist, Dr. Cameron Barrows.
We often associate spring with when nature renews itself. Flowers and baby animals are the icons of spring. Except if you are a lizard. Lizards do breed in spring and early summer; however, it takes about 60 days for those eggs to hatch. Those hatchling lizards will not emerge and greet their new world until mid-summer to early fall. Depending on the year and the availability of food, female lizards will lay anywhere from zero egg clutches (in years when there isn't enough food available produce energy-rich eggs) to one, two or three egg clutches (in years with plentiful food). Each clutch separated by about a month, the time it takes for the females to replenish their fat reserves sufficiently to provide the energy and nutrients to produce more eggs. Fall is (also) the time to celebrate nature's rebirth if you are a lizard lover.
Not all lizards lay eggs. Some, especially those at high elevations, give birth to live young. Putting your eggs in the ground when an early or late frost could kill them is not a good strategy. Keeping your growing embryos inside your body where you can move in and out of patches of warming sunlight makes much more sense. For those, typically lower elevation lizards that do lay eggs, the gravid female lizards excavate nest chambers where they deposit their eggs and where those eggs will incubate until they hatch. That process never ceases to amaze me. The mothers-to-be must dig a nest chamber that is deep enough to be not too hot or too cold, and humid enough, but not too humid (too humid might foster mold or bacteria that would kill the embryos) and not too dry (the embryos would desiccate), and she must select sites that will provide those optimal conditions for those 60 or so days before her eggs hatch. Researchers have found that lizard eggs that are incubated too warm will mature and hatch faster, but they will lack the mental acuity of those incubated cooler and slower. Mental acuity? Apparently, more time in the egg allows neurons to develop more fully. In this case it means the ability to show awareness of potential predators and then take appropriate evasive action. Being incubated too warmly means your chance of passing on your genes to the next generation is far less than those who experienced cooler-slower incubation.
My amazement does not stop there. Imagine when those eggs hatch. It will be totally dark, but they need to find their way to the surface. The mother will have back-filled the tunnel she excavated leading to her nest chamber – both to keep humidity in and so that predators do not find her eggs. In those 60 days of incubation, the tunnel to the egg chamber will have collapsed even further. Yet, despite having never-before exercised their arms and legs, the hatchlings will need to dig to the surface and be ready to both find food and avoid becoming food. Amazing beyond words.
Here in the Coachella Valley, the summer of 2020 broke the record for the number of days that the high temperatures exceeded 100 degrees F – over 150 days, five months straight of blistering heat. That was nearly three weeks more that the previous record. What does that mean for those lizard eggs that were laid before the onset of heat? If being incubated too hot results if fewer hatchlings or hatchlings less able to meet the challenges of life, what does that mean for the Coachella Valley fringe-toed lizards?
This past week the temperatures finally cooled just enough to go out on the sand dunes safely and see how those hatchlings were doing. It was a wet enough spring to have allowed the adult females to build the fat reserves to have multiple clutches; there should be plenty of hatchlings. Community Scientist Cathy Wiley (California Naturalist class of 2019) and I went out on the dunes yesterday. The numbers of hatchling fringe-toed lizards were under-whelming. There were a few, but the ratio of hatchlings to adults was 0.5 to 1. I would have predicted 2-4 to 1 based on the wet spring. The day before I had checked the somewhat cooler dune habitats along the Kim Nicol trail and found the hatchling to adult ratio to be 1.5 to 1, somewhat closer to my expectation. This is too preliminary to identify causes, but perhaps we are seeing the effects of climate change. If so, this is not good.
Perhaps even more interesting, Cathy and I found lots of hatchling flat-tailed horned lizards, and good numbers of hatchling shovel-nosed snakes. We saw the tracks of both (probably dozens of separate hatchling horned lizard tracks) and were able to follow those tracks and find the baby horned lizards on several occasions. So, these two species seemed to be doing well. What is the difference? I can only guess, but perhaps flat-tailed mothers dig deeper (cooler) nest chambers?
There is never any lack of questions to pursue, always another piece of the puzzle to fit into place.
Go outside, tip your hat to a lizard, and be safe.
- Author: Cameron Barrows
A "Natural History Note" From UC California Naturalist's new lead scientist, Dr. Cameron Barrows.
Back in 2016 I published a paper that quantified the added value of volunteer community scientists contributing to field surveys of lizards in Joshua Tree National Park. The reason for the paper was that there was and, in some cases, still is a cultural bias ingrained in many professional scientists against the quality of the data that volunteers collect. If I was going to incorporate citizen scientists into my research, I needed to demonstrate that citizen science collected data were at least as accurate as data collected by “professionals”. For that study we sent a pair of National Park biologists to survey lizards on a half a dozen 300 x 300 m plots. Then I brought a group of 5-7 community scientists out to the same plots a few days later and together we resurveyed each plot. The results were unequivocal. On every plot the community scientists and I counted at least twice as many lizards. More eyes, even if those eyes did not earn a university degree in science, equal more sightings, and so a more complete assay of the lizard population.
Science is perhaps the only way of gaining knowledge that requires going back and repeating experiments to be sure that conclusions are robust. One experiment or one observation is not conclusive. So yesterday, back in the National Park, four community scientists (Tracy Bartlett, Larry Heronema, Jane Spider Fawke, and Pete Schwartz) and I set out to repeat that experiment once again. This time we changed things up a bit; rather than large square plots, we conducted linear surveys along an existing public trail (the Panorama Loop Trail – 7 miles from start to finish) out of the Black Rock campground area. My question was, walking single file along the trail, how many additional lizards were seen by each position in that line-up. I was always in the lead, so my counts were the same as if I was conducting the survey by myself. The 2nd through 5th positions were rotated among the citizen scientists to avoid any observer ability effect. Here are our results:
It should not be any surprise that the first person in line, whether it is me or someone else, would see more lizards. The interesting finding was that each and every position was able to contribute additional sightings, even the last person in line saw lizards that the first four had missed. The reason is that the first person will see the obvious lizards sitting out in the open, and those that move right away, but some lizards sit tight hoping their camouflage will protect them. But, as the next four people walk by, the lizards “lose their nerve” and dart for cover. How long it takes each lizard to dart, dictates which person in line sees it. But then how does that compare to my findings in the 2016 paper? It turns out that the cumulative addition of those four community scientists more than exceeded my count alone. Our combined count was more than double the number of lizards I would have seen if I were by myself – precisely the same conclusion of that I came to back in 2016.
There is no question that community scientists make a huge contribution. In another paper that I am in the final “polishing stage” on before submitting it to a journal for peer review, five California Naturalist community scientists will be included as co-authors because their contributions unquestionably warrant that honor. Not only are the data better, much better, but the discussions we have while counting lizards are tremendously helpful to me for clarifying what questions to address. Yesterday there was much speculation as to what seemed to be fewer lizards than we expected to see. It turns out those musings were right. Comparing surveys made in September-October of each year, in 2018, a drought year, we saw 42 side-blotched lizards. Last year, a wet year, we saw 76, and this year (also a wet spring) we saw just 37. Why? That's where those in-the-field group discussions get fun. We did notice a huge increase in California scrub jays this year; they are omnivorous and would be pleased to gobble down a small lizard. So perhaps successive wet years allow predator populations to build up and then create a top-down dampening of the side-blotched lizards' ability to build their populations. Another question to explore and just another way that community scientists contribute to better science.
However, this pandemic, which has created challenges at every level of our lives, has made it hard to do community-based science and keep everyone safe. We are finding ways that seem to work: small groups of folks who are taking their health and safety, and those of others seriously, masks, and physical spacing. Going forward, because this pandemic will not last forever, if any of you are interested in joining our “Community Science Collaborative” please let me know.
I am adding an image of a desert spiny lizard we saw along the trail.
Go outside, tip your hat to a lizard, and be safe.
- Author: Gregory Ira
The California Naturalist Program's Program Advisory Committee (PAC) is a volunteer advisory group to the Director designed to provide feedback to the program, guide priorities, assist in evaluation, strengthen collaborations, and support program development efforts. I want to thank several of our members who have completed their term and welcome those who have recently joined the PAC. Those completing their term include Dr. Peggy Fiedler (UC Natural Reserve System), Jessica Bautista (UC ANR), Dr. Mark Schwartz (UC Davis), and Dr. Jeremy James (UC ANR Sierra Foothill Research & Extension Center). These members served during a critical period that included the successful completion of the program's Five Year Program Review. Now, we are pleased to welcome new PAC members: Dr. Sam Sandoval-Solis (UC ANR/UC Davis); Dr. Erin Marnocha (UC Natural Reserve System); Claudia Diaz Carrasco (UC Cooperative Extension Riverside County), and Dr. Jairo Diaz (UC ANR Desert Research & Extension Center).
As an existing CalNat instructor, a member of the CalNat Program Advisory Committee, a UC faculty member, a pilot instructor for the new UC Climate Stewards course, and pioneer in natural history-focused participatory science, Dr. Barrows is imminently qualified to serve as the first Lead Scientist for the program. He is currently a Research Ecologist at the Center for Conservation Biology at UC – Riverside working from the UCR Palm Desert Center. He is a recognized ecologist and naturalist who has studied, managed, and explored a huge swath of our diverse state from Humboldt County to the Mojave Desert. He recognizes the importance of the UC California Naturalist program in revitalizing natural history training, increasing trust, engagement and public participation in science, and capturing the sense of urgency that climate change brings to our work.
Over the next three years, we will work together through the CalNat PAC, Quarterly Instructor Calls, and program convenings to build upon our collective knowledge of the best practices that make the UC California Naturalist Program a transformative learning experience for so many people.