Naturalist View July 2010

Desert Plant Adaptations

 Last month, I wrote about how some of the animals of the desert adapt to the extreme temperatures and lack of water of their environment. Now let us look into some of the adaptations that allow plants to exist under the same harsh conditions. Like desert animals, desert plants have adapted to the extremes of heat and aridity using both behavioral and physical methods.

It has been said that desert plants survive because they have thorns, spines, taste bad or are poisonous. As true as this may seem, it’s not that simple. Anybody that has wandered in the desert has become aware of the plants’ defensive armor of thorns and spines. Most of us have had encounters with the “Jumping Cholla.” Of course, they really do not “jump,” but instead cling with their spines to anything that brushes ever so slightly against them. Many other desert trees and shrubs have also adapted by eliminating leaves and replacing them with thorns - or by greatly reducing leaf size. Such plants, like the Palo Verde, also usually have smooth, green (chlorophyll) bark on stems and trunks serving to both produce food and seal in moisture.

Xerophytes: Plants that have adapted by altering their physical structure are called xerophytes. Xerophytes, such as cacti, often have special means of storing and conserving water. They have few or no leaves; this reduces loss of water due to evaporation. Xerophytes are the largest group plants living in the deserts of the American Southwest. The Sonoran Desert is home to an incredible variety of succulents including the giant Saguaro Cactus, Mesquite, Paloverde, and Ironwood. A succulent can be defined as a plant that stores water in its tissues as a mechanism to survive periods of drought.

Phreatophytes: Plants that have adapted to arid environments by growing extremely long roots, allowing them to acquire moisture near the water table, are called Phreatophytes. A good example is the mesquite; its roots are the longest of any desert plant. Mesquite roots have been found in a copper mine shaft 160 feet beneath the surface. However, 90% of the roots of a mesquite remain in the top 3 feet of soil. The deep taproot helps the plant survive drought, while the surface roots are ready to soak up the scarce rainfall of the winter or the sudden downpour of the monsoon.

Two native mesquite trees, the Honey Mesquite and the Velvet Mesquite, are native to Saddlebrooke. Other species of Mesquite have been introduced into the area for landscaping. The Creosote bush is also one of the most successful of all desert species, because it utilizes a combination of many adaptations. Instead of thorns, it relies for protection on a smell and taste that wildlife find unpleasant. It has tiny leaves that close their stomata (pores) during the day to avoid water loss and open them at night to absorb moisture.

Other desert plants using behavioral adaptations have developed a lifestyle in conformance with the seasons of greatest moisture and/or coolest temperatures. These types of plants are referred to as perennials, plants that live for several years, and annuals, plants that live for only a season.
Desert perennials often survive by remaining dormant during dry periods of the year, then spring to life when water becomes available.
A familiar perennial is the Ocotillo. It survives by becoming dormant during dry periods, then coming to life when water becomes available. After rain falls, the Ocotillo quickly grows leaves to photosynthesize food. Flowers bloom within a few weeks in April When seeds become ripe and fall, the Ocotillo loses its leaves again and re-enters dormancy. During the summer monsoon the Ocotillo will often produce a new set of leaves but no new blossoms. The Ocotillo also has a waxy coating on stems which serves to seal in moisture during periods of dormancy.

Another example of perennials that utilize dormancy as a means of evading drought are bulbs, members of the lily family. The Coyote gourd has a bulb that springs to life after the summer monsoon, sending out 20 foot runners with yellow flowers that develop into the orange sized gourds. The fruit pulp contains toxic and extremely bitter chemicals that humans use to make soap, which reportedly repels body lice. Natives eat the nutritious seeds, which contain up to 35% protein and 50% fat. Coyotes and some other animals can eat the seeds even when tainted by the pulp. Javelinas eat tuberous roots, which they can sniff out even when there is no vine above ground. Native people have used the gourds as containers and dance rattles since prehistoric times.

Annuals (Ephemerals)
The term "annual" implies blooming yearly; but since this is not always the case, desert annuals are more accurately referred to as "ephemerals." Many of them can complete an entire life cycle in a matter of months, some in just weeks. Desert plants must act quickly when heat, moisture and light inform them it's time to bloom. Ephemerals are speedsters of the plant world, with flower stalks bursting out in a few days. The peak of this bloom may last for just days or several weeks, depending on the conditions. Most annual desert plants germinate only after heavy seasonal rain, and then complete their reproductive cycle very quickly. They bloom profusely for a few weeks in the spring, accounting for the annual wildflower displays of the deserts. Depending on the winter and spring rains, these displays can be spectacular or hardly noticeable. The seeds left behind that are not eaten by the birds, small mammals and insects may lie dormant for years until conditions are right for germination.

• Mesquite Tea: Place 1 lb. of mesquite pods in 1 gallon of water. Boil pods, at a rolling boil, for 30 minutes. Remove pods & strain. Cool broth & serve over ice.

• Mesquite BarBQ: All those mesquite pods lying around that need to be picked up can be used instead of expensive mesquite firewood or charcoal on your BarBQ. I recommend soaking the dry pods in water for 10-20 minutes then throw them directly on the briquettes or grill and cover to impart that mesquite flavor.

I have been very busy picking up pack-rats, mice etc. that residents have been live trapping and wish to thank you all for not using poisons. I only had one secondary poisoning in May, a dove that had feed on some poison seeds that had probably been intended for something else.

Naturalist View June 2010

Adapting to the Heat

One warm afternoon last summer, I was trying to get a picture of a SGB (Small Gray Bird) with my telephoto lens. This bird was busy hunting for food, and like most SGB’s, would not pose for any length of time for a photo. I am a reasonably patient man (ha!), but this bird kept in the shade. I thought that it would soon land in a sunny spot so that I could get the shot I needed for identification. It became evident that this was not happening. Eventually it dawned on me that what I was observing was an adaption that this bird had made to the summer heat. By staying in the shade, it could keep from overheating as it was gathering food. I observed this bird over the next few days and found that this behavior was consistent; it never did give me an opportunity to take the picture I wanted.Nature always has found ways to adapt to environment. The big challenges for adapting to the Sonoran Desert are the heat and water. Let’s take a look at how some local animal species adapt to our area.

A nocturnal lifestyle, which keeps them out of the heat of day (and out of human sight as well). The mountain lion is a good example. The wide variety of prey the cougar hunts ranges from rodents and rabbits to cattle and deer. This solitary animal can travel miles in search of food. The mountain lion has adapted itself well to the environment of the Sonoran Desert. It only hunts during the night, while during the heat of the day it takes shelter in caves and crevices in the mountains. You may be more familiar with the nocturnal roaming of the Javalina, the ringtail cat or the desert toads. Even the small rodents such as the white-throated wood rat (pack rat) are essentially nocturnal.

Living in burrows, which are cooler and more humid.This often goes along with the nocturnal lifestyle, and the burrow becomes a place to sleep during the hot day. Burrow diggers are called fossorial. One of my favorite fossorial residents is the round-tail ground squirrel. Round-tailed ground squirrels are social, living in small colonies. They hibernate through the winter months, emerging in early February to take advantage of the new spring growth. They breed shortly after coming out of hibernation; 6 to 7 young are born in March or April. By May, the youngsters accompany the mother to the surface. The young come out for several hours of playing and feeding until the temperatures rise; then they return to their burrows until late in the afternoon when temperatures start to cool. They stand on their hind legs trying to get a better view as they watch for their many predators. Because they depend on vegetation for moisture, these squirrels estivate (Estivation is another form of dormancy, or "sleep") for a few weeks during the summer drought, until the summer rainy season again brings new growth and food.

Slender bodies with long limbs - are better for shedding heat. Snakes and lizards are good examples. They can move from one shady spot to another without absorbing as much heat. Lizards run by lifting their bodies and running on their tip-toes to keep their body from coming in contact with the hot ground. You may have noticed lizards doing push-ups. These are complex forms of lizard communication which can mean such things as “Hello, Gorgeous” or “Get your skinny rump off my rock.”

Adaptations for reducing water loss - specialized snouts and efficient kidneys are all part of this strategy. Some animals - i.e. the kangaroo rat - are so efficient that they never need to drink liquid water; they get all their water from the food they eat (including the water released when sugars are respired to form CO2 and water). Kangaroo rats have large cheek pouches that open on either side of the mouth and extend back to the shoulders. They fill the pouches with food, such as dry seeds, and then empty them by turning them inside out, like pockets. The overall color of the kangaroo rats can be anywhere between pale, sandy yellow, to dark brown, with a white underside. Tails tend to be dark with white sides and a tuft of longer hairs. A feature of the kangaroo rat is the animal's efficient kidneys. The kidneys recycle almost all of the water which is retained by the body. Even the nasal passage of the Kangaroo rat is large flat and convoluted so that H2O exhaled in the breath is condensed and reabsorbed. They also do not urinate and as a result do not have the strong odor of other rodents. Kangaroo rats lose water mainly by evaporation during gas exchange, and so have developed a behavioral adaptation to prevent this loss. As they spend a lot of time within their burrows to escape the heat of the day, the burrows become much more humid than the air outside (due to evaporative loss). When collecting seeds, they store them in the burrows rather than eating them right away. This causes the moisture in the air to be absorbed by the seeds, and the kangaroo rat regains the water it has previously lost when it then consumes them.

Because of this tremendous concentration ability, kangaroo rats never have to drink; the H2O produced metabolically within their cells during oxidation of foodstuff (food plus O2 yields CO2 + H2O + energy) is sufficient for their body. Also, kangaroo rats cannot lose water by perspiring, because they have no sweat glands. Kangaroo rats lose water mainly by evaporation during gas exchange, so have developed a behavioral adaptation to prevent this loss. As they spend a lot of time within their burrows to escape the heat of the day, the burrows become much more humid than the air outside (due to evaporative loss).

These are just a few examples of animal adaption. Keep in mind that any plant or animal that is native to the area has made the adaptations necessary to survive here. Learning about these adaptations is a lifelong fascinating mystery.

Wrestling Rattlers

Several people sent me these pictures taken by Saddlebrooke resident Linda Andrews. This was not a mating dance but was a “Combat Dance”. In the spring snakes are looking for a mate. In the snake world this accomplished with a sense of smell. A male will come across the “perfume” of a mature female and follow the scent to locate her. Since several males may be “on the trail” they often come across each other. In the case of rattlesnakes this may result in a dominance display or serpentine wrestling contest, rearing and falling and body slamming until one or the other concedes defeat and leaves the area. Once inseminated the female, after a gestation of 167 days will bear her brood live, in late summer. The young are born complete with fangs and venom, armed and dangerous at birth.

The Western Diamondback Rattlesnake, Crotalus atrox, Crotalus comes from the Greek word crotalon meaning a rattle or a little bell; atrox comes from the Latin word atroc which means hideous or savage. Actually I find Rattlesnakes to be rather beautiful and certainly not savage. They have no desire to be near you or to waste their precious venom on something far to big to swallow.