Wednesday, May 10, 2017


Last week, fellow docents and I were having a conversation, prompted by a question to one of them from a visitor, regarding the relationship between a palo verde and a saguaro. It was obvious from our discussion that we needed a review of symbiotic relationships!

Symbiosis is defined as a relationship between two or more organisms that live closely together. There are three main types of symbiosis: commensalism, mutualism and parasitism. Commensalism is a relationship in which one organism benefits and the other is unaffected. Mutualism is a relationship in which both organisms benefit. Parasitism is when one organism benefits and the other one is harmed. To be successful, a symbiotic relationship requires a great deal of balance. Even parasitism, where one partner is harmed, is balanced so that the host lives long enough to allow the parasite to spread and reproduce.

These delicate relationships are the product of long years of co-evolution. Bacteria were the first living things on the planet, and all of Earth's other creatures have been living and evolving with them for hundreds of millions of years. Today, microbes are essential for many organisms' basic functions, including nourishment, reproduction, and protection.

So, back to the saguaro/palo verde relationship. The visitor wanted to know, if the nurse tree was benefitting the saguaro, what the payoff was for the palo verde? How would you classify that? The saguaro benefits from the protection provided by the palo verde. But, how about the palo verde? Most of the time, their relationship is probably commensal - benefiting the saguaro and causing no harm to the palo verde. However, in times of drought the shallower root system of the saguaro may intercept most of the rainfall.  These two species would then be said to enter a type of symbiosis known as interspecific competition. The saguaro could eventually hasten its nurse tree's death.  

There are thousands (millions?) of symbiotic relationships in the Sonoran Desert. Just take the saguaro, for example. Think of all the animals that depend on the saguaro for food, or shelter. The saguaro, in turn, depends on certain species to pollinate it, and to disperse its seeds. Bees, bats and white-winged doves get a food reward, while doing the important work of helping the saguaro to reproduce.

Parasitism - The desert mistletoe is an example of a parasitic symbiont that depends on its host,

usually a legume tree, for nutrients. The host tree is harmed over time and with heavy infestation of the mistletoe by the depletion of nutrients. 

Other common parasitic relationships include the coyote and the flea, or the mange-causing mite. Female mites can burrow into the skin. Coyotes with mange can lose their hair, which can make it difficult for them to control their body temperatures. Mange must be extremely severe before it disables a coyote. Most coyotes can survive with the disease for a long time. The brown-headed cowbird parasitizes the nests of other birds, called brood parasitism. The cowbird benefits by having another bird raise its young, which are usually larger than the bird’s own young and can out-compete them for food and space.

Animals are parasitized by viruses, bacteria, fungi, protozoans, flatworms (tapeworms and flukes), nematodes, insects (fleas, lice), and arachnids (mites). Plants are parasitized by viruses, bacteria, fungi, nematodes, and a few other plants.

Mutualism - Examples of mutualism abound. Just think about flowers and their pollinators. That’s a
win-win for both parties. Not all symbiotic relationships are visible by humans. Take the bacteria that live in the guts of herbivores, helping them to digest plant material, which is more difficult to digest than animal prey. This gut flora is made up of cellulose-digesting protozoans or bacteria living in the herbivores' intestines. Another example is the bacteria that allow legumes to fix nitrogen in the soil, living on nematodes on the plant roots.

Commensalism - Commensal relationships may involve one organism using another for transportation or for housing or it may also involve one organism using something another created, left after its death (metabiosis). Examples of metabiosis are hermit crabs using gastropod shells to protect their bodies. Birds nesting in trees is a commensal relationship. Vines use trees to reach up to the light, causing no harm to the tree (most of the time!).  Consider the packrat home and all the many critters that seek shelter and food there.

Symbiosis can either be obligate or facultative (optional). In obligate relationships, one organism cannot live without the other. Perhaps one of the most well-known obligate mutualistic relationships is that of the yucca moth and its host plant.

The yucca moth, also commonly called the pronuba moth, is a small white moth that lives in the semi-arid habitats where yucca plants grow. The yucca moth is well-known for its co-dependent relationship with the yucca plant. The yucca moth’s larvae rely exclusively on the seeds of the yucca plant as a primary food source, and the plant relies exclusively on the yucca moth for pollination. One cannot exist without the other, creating an obligate mutualism between the moth and the plant. 

We talk about Keystone Species - a plant or animal that plays a unique and crucial role in the way an ecosystem functions. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. These are species on which so many other species are dependent. Think about the saguaro, and prairie dog, and the many different species for which they are so important. Another good example is the cottonwood tree and the many creatures that depend on it. I’m sure you can think of many more relationships in biology, for I haven’t begun to scratch the surface.  I have discussed only the 3 main types of symbiosis.  There are many more, and perhaps those are topics for another article.

We do well to remember that in each of these types of symbiosis, few situations are absolute.  In most cases, there is a continuum of types of interactions between species, rather than an exclusive category.

Tuesday, November 29, 2016

Turning Down the Noise

There are few ailments of the body and soul that cannot be soothed by a walk in nature.  And, thus it was that post-election depression sent my like-minded friend and co-worker and I up into the Tucson Mountains for our annual trek to Wasson Peak. At 4687', Wasson Peak is the highest point in the Tucson Mountains on the west side of Tucson proper.  While there are several ways to access the peak, the trail we chose this time was the Camino del Cerro, leading up the east side of the mountains, 9.6 miles round-trip.

The low elevation and lack of cover make this definitely a hike for the winter, and this November day proved to be a perfect time - a light cloud cover, temperatures in the 70's, and a few breezes.

Leaving the trailhead parking lot, you immediately enter Saguaro National Park West. We had gone but perhaps a quarter of a mile when we spotted the first mule deer, and soon we encountered several more - 8 in total - watching us as we watched them.

Beautiful low-desert vegetation surrounded us - giant saguaro cactus, palo verde trees, ocotillo, prickly pear, barrel and cholla cactus.

As the trail rose in elevation, subtle changes occurred in the plant community.  Sotol (desert spoon) and jojoba appeared and soon became abundant.

The trail was mercifully quiet on this Tuesday morning and we met only one other hiker before reaching the 'saddle', where trails converge and meet the final leg to the top.  There it was time to have a brief rest and snack before tackling the steepest part of the trail.

Another 1.2 miles to the top and the legs were burning.  But once there, what glorious 360° views of the entire valley!  Such a fine spot for lunch, especially on this day of little wind.  Several other hiking parties shared the space, mostly visitors from Canada.

Then it was time for the descent. Another 3 hours of peace and beauty, undisturbed by political discussion, the news, television, the too-often ugliness of real life. There were few flowers blooming after a long dry spell, but a few desert zinnias and purple filaree added color, as did the bright red fruit of the Christmas cholla and the beautiful yellow fruit of the barrel cactus.   Bright neon green lichen decorated the north-facing rocks.  We marveled at the glowing spines of the teddy bear cholla, which looks deceivingly cuddly.  Lovely reddish tanglehead grass made a nice contrast to the brown and green palette.

Back at the trailhead parking lot, we were disturbed to see trash littering the ground all around the overflowing container, and cigarette butts everywhere.  Yes, we're back in 'civilization'.

Wednesday, May 11, 2016

Docent Diaries - An Update from the Desert Museum

Tucson, Arizona

After a busy winter season, things are beginning to slow down at the Desert Museum.The heat is ramping up, getting ready for summer's blast. Out-of-town visitors find somewhere cooler to go.  Afternoon tours are eliminated. Winter visitors are leaving town. The docent corps, too, is thinning out.  But, for those of us who brave the warmer temps, things are always exciting at the Museum.

Our Cactus Garden has undergone a transformation in recent months and is now a stunning showcase for all things spiny.  Friday docents give a tour every week of the garden, and visitors are fascinated by the shapes, colors and adaptations of cactus from the Sonoran Desert as well as more tropical locales farther south.  I love giving these tours and last Friday I had six enthusiastic visitors learning about what is, and what is not, a cactus.

The cactus blooms were sort of in a lull, but there was this lovely, mounding Notocactus.


And this Mexican night-blooming cereus, which was just starting to close after its nighttime shift. Interestingly, the one in my garden bloomed the same night, for the first time ever.

Mexican Night-Blooming Cereus

Not to forget our amazing saguaro cacti that are still blooming full blast.

Friday is a popular day for school groups to visit the Museum.  A good thing or a bad thing, depending on your point of view.  As a docent, I love having the schoolkids come out, and I am especially  happy when they are well-chaperoned and have been given learning assignments.  After the Cactus Garden Tour, I was stationed in the Ethnobotany Garden and I had a group of high school girls who listened intently and asked great questions.  First, I had to explain what ethnobotany is! Just a big word for how people use plants.  They loved tasting the mesquite flower, and feeling the texture of the jojoba oil.

Near the People and Pollinators Garden is the Maze Garden where I found a gorgeous Desert Willow (Chilopsis linearis) covered in deep magenta flowers. This is not a true willow, but a member of the Bignonia family.  Large, fragrant, orchid-like flowers cover the plants from April to August in a range of colors from white to this fuchsia color.

But my real mission was now down the path in the Big Horn Sheep area, where not one, but two, lambs have recently been born.  There's no doubt that all babies are adorable, but these lambs take the cuteness factor to a whole new level.  Within just days of birth they are scrambling up the steep cliff of the enclosure, bouncing and leaping all over.

The two ewes are mother and daughter.  The lambs, one a ram and one a ewe, were born one month apart, first to the mother and then to the daughter. Playtime is followed by a crash - moms and babies find a spot in the shade to get some rest. Along with the visitors, I could watch these guys all day! We'll have the pleasure of watching them for another 8 months or so before the lambs are shipped off to another facility.

Time for lunch and our monthly potluck.  There's always so many fun dishes to try, and oh! the desserts! This was a special one as we were honoring our day captains at the end of their tenure.  Each docent day has two captains that serve for one or two years, doing the scheduling and keeping us docents in line.  Sort of like herding cats.  We are thankful that they are willing to do the job, which can be stressful and frustrating.  I know.  I've been there!

Martha, Rae, Carole, Marsie
Outgoing captains Rae and Marsie, with incoming captain Martha, and me

Animal handling is one of the great privileges and rewards of being a docent.  Each year we choose the categories of animals we want to handle, and then go through training and certification on each.  This year, my animals are snakes and middleweight raptors.  Everybody loves the big birds, of course.  But the snakes, not so much.  So, it's especially important to educate visitors about snakes, and perhaps change their thinking a bit.  On this day, I had a large common kingsnake.  It's amazing how many people's first question is, "Is it poisonous?"  Right.  I'd be fool enough to stand here holding a venomous snake.  Kingsnakes, which are constrictors, prey on a variety of small animals, including other snakes.  Famously, even rattlesnakes are on their diet.  Which leads people to classify kingsnakes as 'good' snakes.  I gently inform them that there's no such thing as 'good' or 'bad' snakes. All snakes are just trying to make a living, using the tools they've been given.

There were still many more sights to see as the day went on.  Passing a very large saguaro, I could hear baby birds calling.  Just then this male Gila woodpecker poked his head out of the nest.

It is the male woodpecker who does the work of excavating the hole in preparation for nesting, and then he shares the duties of caring for the nestlings.  Right after I snapped this photo, off he went, most likely in search of more food for those ravenous babies.

Baby animals are everywhere on the grounds.  Black-tailed prairie dog pups have emerged from their burrows and are providing a never-ending source of entertainment.

One lucky pup was getting a serious grooming from mom.

Last stop of the day was in front of the mountain lion exhibit.  Our young male, Cruz, was feeling frisky.

Big Stretch
And then, he decided to talk to us.


Have you ever heard a mountain lion meow like a housecat?  Well they do, and it sounds so odd coming from this big cat.  Mountain lions are the largest of the small cats - those that meow and purr.  The big cats roar.

That was a perfect ending to a most excellent day!

Sunday, May 1, 2016

Gila Monster - A Visit from an old Friend

What's black and orange and beaded all over? Why, a big, fat, venomous lizard, that's what!

The Legendary Gila Monster, that almost mythical creature of the Wild West, about whom tall tales are told, about whom superstition and myths abound. And yet, here he is, right in my back yard.  I consider myself among the lucky ones who have actually seen a Gila monster in the wild.  Some people live their entire lives in the Sonoran Desert and never encounter this fascinating creature.  

Even the name, 'monster', is absurd and reflects the amount of misinformation and exaggeration about a lizard that is barely two-feet long, slow and lumbering, shy and non-aggressive.  Perhaps it's the elusive nature of a creature that spends 90% or more of its life underground, hidden from view, and about which, as a result, not a lot is known. 

The Gila monster is one of only two venomous lizards in North America, and the only one in the U.S. The other, the Mexican beaded lizard, lives exclusively south of our border, in Mexico and into Guatemala.  Gila monsters are known as nest raiders, and since they prey almost exclusively on food that will not run away from them - baby rabbits, bird eggs, baby lizards - their venom is not needed to subdue prey as is the venom of rattlesnakes, for instance.  So, what's the purpose of the venom? Defensive?  It seems the most logical.  The venom gland is located in the lower jaw, and travels through the grooved lower teeth to enter the victim, producing excruciating pain.  Just in case you were thinking of getting away after being bitten, the Gila monster's other trick is to not let go, continuing to gnaw, increasing the venom delivery and making sure you are plenty sorry you harassed him.  Not to worry, however, you won't die from the venom.  And that's the good news.  The bad news is that you'll probably wish you would!

The beautiful black and orange/pink beaded pattern is unique to each individual lizard.  The genus name, Heloderma, means studded skin. The 'beads' are actually bony scales, making the lizard's skin extremely difficult to penetrate and providing a good defense against large predators such as coyotes. Two subspecies differ in the beading patterns - banded, with regular, well-defined bands all over; and reticulated, with the irregular pattern such as the one shown in the photo.  The reticulated is the species of southern Arizona and the only one I've ever seen.   Oddly enough, all newly hatched Gila monsters are banded, but the ones in our range (Heloderma suspectum suspectum) develop the reticulated pattern as they mature. The small western banded gecko is sometimes mistaken for a baby Gila monster.  

A forked tongue, like that of snakes, gives the Gila monster an extremely good sense of smell, and allows it to locate even buried eggs.  Emerging from the winter den in spring, the Gila monster goes looking for food, and may gorge itself when food is available, storing fat in the tail for the long, lean months ahead.  A mate is also on the agenda, and, if that quest is successful, the female lays eggs in July or August, burying them in the sand.  The eggs overwinter and hatch in the spring.  

In recent years, research on Gila monster venom has led to the development of exenatide, a drug that is a synthetic form of a substance found in Gila monster saliva, for the treatment of Type II diabetes. It helps control blood sugar levels and leads to weight loss. 

Many years ago, we named a visiting Gila monster Albert.  Since then, every one who comes to our yard is known as Albert.  I suppose it would be possible to compare photos and see if Albert is one individual or many different ones.  I prefer the mystery.  See you again next year, Albert.

The End

Sunday, April 10, 2016

A Walk in the Spring

All of a sudden, it seems, the colors of the desert burst forth, and for a short, glorious time, flowers everywhere are advertising their wares to potential pollinators and awed onlookers.  From prickly pear to cholla, saguaro to palo verde, the desert is going crazy.  My walk around the neighborhood was slowed by the urgent need to photograph every flower.  Of course, I didn't get them all, but here's a little taste of what enamored me so.

First, the flowers . . .

Cholla Cactus

Cholla Cactus Flower

Ocotillo, Saguaros, Palo Verde

Prickly Pear Cactus

Cholla Cactus

Cholla Cactus Flower

Saguaro Cactus

Cholla Cactus

Prickly Pear Cactus

Prickly Pear Cactus

Prickly Pear Cactus

Cholla and Palo Verde

Purple Prickly Pear

With Yellow Flowers

Strawberry Hedgehog Cactus

Prickly Pear Flower

White Ratany

Twining Milkweed Vine

Purple Prickly Pear surrounded by Catclaw Acacia

Blue Palo Verde

Blue Palo Verde Flower

Yellow Bird of Paradise

But, it wasn't all flowers.  Some of the other sights . . .

Phainopeplas and Dove in Ocotillo

Cooper's Hawk

Beautiful Long-Nosed Snake

The snake's tail
 And, when I got home, who should come to visit?  This handsome fellow.
Desert Kingsnake
All the flowers are somewhat early as we've had a warm, dry spring.  After the blue palo verdes bloom, come the more numerous foothills palo verdes, which will turn the entire landscape yellow with their beautiful blooms.  They are slightly paler yellow than the blue PV flowers due to the presence of the white banner petal.  So the show will go on for a while.

The Sonoran Desert in spring will forever alter your perception of "desert" in a good way!