- 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
A "Natural History Note" From UC California Naturalist's new lead scientist, Dr. Cameron Barrows.
When scientists underestimate complexity, they fall prey to the perils of unintended consequences. Siddhartha Mukherjee
About five million years ago the uplifting Colorado Plateau changed regional drainage patterns and in doing so created the Colorado River. The Colorado River extends into western and southern Colorado where, depending on the year, the annual snowpack can yield very different flows down the river. Some years, by summer the river would run dry. Other years massive floods scoured through the Plateau's layers of sandstone (creating the Grand Canyon) and would sometimes shift the course of the river into the Salton Trough forming an immense lake (christened by geologists as “Lake Cahuilla”). Water flows toward the lowest point on a landscape, and at 277 ft (84.3 m) below sea level, the tough is one of the 10 lowest terrestrial elevations on earth. The lake's historical shoreline can be easily seen on the hillsides along the eastern edges of the Santa Rosa Mountains. Once the lake filled to an elevation equivalent to sea level, the river would return to its bed and empty into the ocean where it formed one of the largest estuaries and riparian forests in North America. After decades of summer heat the lake would incrementally evaporate and then finally disappear leaving a salt pan coating the lowest regions of the basin. Eventually the river would flood again, resurrecting Lake Cahuilla and repeating this cycle again and again…. a pattern of establishment, decline (drying), and then renewal (re-filling to its former self), again and again. An extensive sand dune system formed at the southeast edge of Lake Cahuilla, formed from sands carried by the flooding Colorado River, sand that eroded out of the sandstone that once filled the space that is now the Grand Canyon. When the basin was dry, northwest winds would blow those lake bottom sediments into sand dunes. We now call those dunes the Algodones, and where those dunes formed along the edges of the great estuary, they form what is the Gran Desierto in northwest Sonora, Mexico. Those sands, as well as other dune systems created by the flood cycles of the Colorado River, provided isolated dune fields where fringe-toed lizards thrived and eventually diverged into what today are six recognized species.
It would be hard to fully appreciate the biological richness created by Lake Cahuilla. The river would have delivered both water and fish to fill the lake. The fish then would form the base of a food web that would include millions of pelicans, cormorants, terns, grebes, and ducks, with storks, cranes, herons, rails, and egrets hunting along the shores. Some would have formed nesting colonies on the islands that would have been created by the lake. The filling of the lake would increase groundwater levels resulting in cottonwood, willow, desert fan palm, and mesquite forests becoming established along what are now ephemeral drainages. Those forests would have been populated by warblers, flycatchers, cuckoos and vireos. Some early visitors suggested jaguars may have hunted for deer and peccaries beneath the canopies of those forests. When the lake was dry, lush vegetation and aquatic species would then be concentrated at a few perennial springs and creeks. The millions of birds would have needed to shift elsewhere, to the Colorado River's estuary in the Gulf of California to the south and to lakes along the eastern base of the Sierra Nevada. Those isolated springs and creeks within the Salton Trough would sustain some species, albeit in low numbers, until the next filling of the lake. Sometimes that isolation, resulted in the evolution of new species. The Salton Sea Springsnail, Pyrgulopsis longinqua, is found only in the Salt Creek wetlands and nowhere else on earth.
The first humans to experience and document this ebb and flow and renewal of sand and water were the Cahuilla, as told through their oral traditions. For thousands of years, they enjoyed the cornucopia of resources when the lake was full, and their populations swelled. They caught fish and birds, enjoying the riches the lake provided, that were in contrast to the surrounding parched desert. When the lake was dry the Cahuilla moved into canyons where perennial water was still available and migrated seasonally up or down the mountain slopes to take advantage of agaves, pinyon seeds, acorns from oak trees, and junipers, along with deer and bighorn sheep. It was sometimes many decades and even centuries between floods sufficient in magnitude to jump the banks of the Colorado River, finding the low Salton Trough and filling the lake once again, so the Cahuilla needed versatility to survive. Prior to modern times, the last time Lake Cahuilla filled was in the 1400s, just before Christopher Columbus landed in the Caribbean Islands and set-in motion a migration from Europe to North America that would alter the lives of the first people of North America, and the natural diversity of this continent, forever.
In modern times the Colorado River may have flooded sufficiently to jump its banks for the final time in 1906. Engineers were creating a canal system to deliver water to meet the needs of a shift in land use to agricultural expansion in both Imperial and southeastern Riverside Counties when floodwaters broke through their canal and filled Lake Cahuilla once again. Multiple dams subsequently built on the Colorado river to siphon away water to quench the thirst southwestern cities will eternally regulate flows down the river, preventing any future flooding, preventing any future inputs of relatively fresh water to the Salton Trough. The building of dams on the Colorado River has forever changed the ebb and flow, flooding, drying and renewal cycle of what was once Lake Cahuilla, changing its character and changing its name to the Salton Sea. Entrepreneurs once thought that the Salton Sea would become a sportsman's mecca, providing fishing, boating, and waterskiing experiences like no other. There were a few decades where that dream seemed to be true. Then it wasn't.
Rather than drying up as it had so many times before, water running through the canals, through agricultural fields to hydrate crops and to dilute salts accumulating in the soils, drains into the Salton Sea and has, until recently, kept the lake from drying. That agricultural wastewater – “drool” – adds four million tons of salt into the Salton Sea annually. The Salton Sea currently has a salt concentration of 44 g/L, or about 25% saltier than the ocean. Some of that water once dedicated to solely to agriculture is now being sent to fill the faucets of a rapidly growing population in San Diego, so less drool for the Salton Sea, and it is now shrinking fast.
The flood and drying cycle that created the ephemeral Lake Cahuilla is what is called an ecosystem process – energy and resource inputs that create ecosystems that are the foundations for biodiversity. Alter an ecosystem process and there will be consequences to biodiversity. Fish can no longer live in the Salton Sea – it is too salty. The food web has been severed for fish-eating birds. There is little doubt that the Salton Sea will continue to shrink and continue to get saltier. There are of examples of what the Salton Sea's future could be. Those lakes that occurred along the eastern base of the Sierra Nevada have been similarly altered by water diversions to fuel Los Angeles' growth. One, Owens Lake, is now dry and toxic alkali dust blows off its dry bed. Another, Mono Lake, was headed in that same direction. A friend and mentor, David Gaines, spearheaded a battle to redirect a couple Sierra creeks back to their natural flow to stabilize Mono Lake. In a true David and Goliath fight, David won. Mono Lake has a salinity of 79.8 g/L, far saltier than the Salton Sea, but there is life there. There are of course no fish, but a food web does exist with algae, brine shrimp, and brine flies at its base. California gulls nest there and thrive, and eared grebes and Wilson's phalaropes use it as a critical refueling stop on their annual migrations, all gorging themselves on shrimp and flies. Back at the Salton Sea, the food web is already in transition from fish to invertebrates. No longer kept in check by hungry fish, the population of an insect called a water boatman (Corixa punctada) has exploded. The boatmen populations are so large that they are expanding beyond the confines of the Salton Sea, sometimes landing in backyard swimming pools throughout the Coachella Valley. Birds that are not fish-eating specialists can and do make a meal of the boatmen, and over time brine shrimp populations may become established when the waters become too saline for the boatmen. Nevertheless, pelicans, cormorants, terns, and other fish-eating specialists are among the first losers in this ecosystem transition.
Unlike before water diversions, there are no remaining lakes on the eastern side of the Sierra Nevada that can replace what was Lake Cahuilla, and due to the water diversions from the Colorado River that take nearly every drop before it reaches the Gulf of California, the estuary the estuary at the once great river's mouth no longer supports the biodiversity it once did. The Salton Sea was a last refugium, until it wasn't. Other losers are the people who live anywhere near the Salton Sea. As the Sea shrinks, exposing an ever-widening shoreline, winds blow alkali dust into communities of the folks, many of whom work the agricultural fields that put food on our tables. Respiratory diseases are already showing up. The cascade of impacts stemming from altering this ecosystem continues.
There are places that, at a much smaller scale, provide some resemblance of what Lake Cahuilla once was. One is the Dos Palmas Preserve, but that will be another story.
Go outside, tip your hat to a lizard (and a cactus), and be safe.
- Author: Gregory Ira
We can rise to challenges, or we can resign ourselves to fate. Many have been quick to label 2020 as a “bad” year, as if we had no role in its making or how we respond to it. The challenges were real: a global pandemic, a renewed fight for racial justice, the increasingly present manifestations of environmental change, all converging on an already unequal economy. Yet, all of these were familiar challenges and unfortunately none of them will magically disappear when we ring in the new year. The true measure of any year isn't simply what came our way but how we responded to it.
I've been deeply gratified, heartened, and encouraged by the response from our community of naturalists, our partner organizations and our CalNat team. It is worth taking a few moments to reflect on this last trip around the sun.
In March of 2020, the California Naturalist Team shifted gears quickly when we realized that our annual plans for the program weren't going to happen as usual. Exactly half of scheduled CalNat courses (18 of 36) from late February to December were cancelled. In response, staff focused on: updating our program content; identifying safe alternatives for course delivery and contactless volunteer service opportunities; transitioning training and convening to online formats; and pursuing grant funding for our program and partners. Over the last eight months we conducted three online Project Learning Tree workshops, two online instructor training workshops, organized an invasive species monitoring training, launched the first three webinars in our new CONES series, prepared three grant proposals, and successfully piloted the new UC Climate Stewards course. We also completely updated our program's strategic goal on diversity, equity and inclusion.
Our partner organizations also responded. Many shifted to online course delivery. Others adjusted group size and delivery methods to offer courses that ensured program quality and participant safety. All our partners shared the lessons they've learned freely. In one case, Dr. Laci Gerhart-Barley's course produced a paper for the journal Ecology and Evolution entitled, “Teaching An Experiential Field Course Via Online Participatory Science Projects: A COVID-19 Case Study of a UC California Naturalist Course.” Others put their courses on hold but used their naturalist knowledge to engage their clientele through livecast or recorded virtual field trips. Almost everyone rediscovered nature in their immediate surroundings whether it was their backyard, a tree outside their window or a local park. Finally, while very few escaped the challenges of 2020, so many of you still found a way to give back to the growing number of people and organizations who are barely struggling to get by.
Like its name suggests, 2020 brought into focus significant challenges to our vision of environmental stewardship. Our best science falls flat if it lands on deaf ears. Our individual actions, while important, need to be scaled up to match the level of the problems before us. Our ideals of racial justice can't be separated from other aspects of our work. And no matter how difficult our conditions may get, we still have the capacity to give. By this measure, 2020 has been a year of transformational learning. It challenged our assumptions and our perception of what is needed for environmental stewardship. Like the vaccines that will activate antibodies in our bloodstream, 2020 was the shot in the arm we needed to reinvigorate our efforts to build more resilient and equitable communities and ecosystems.
- 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.