On January 2, 1998, I was walking through the desert ecosystem of Papago Park located along the eastern city limits of Phoenix, Arizona, when I discovered the trunk of a dead ironwood tree in a sandy wash strewn with rocks, shrubs, and other tree trunks. The soil in the wash was slightly moist, due to rains from the previous week. Upon turning over the ironwood trunk, I noticed three millipedes, Orhtoporus ornatus (Laughlin 34), trying to crawl away from the sunlight and back into the damp soil, their preferred environment. Damp soil is important for the survival of the millipede because its food source, bacteria, thrives there.
Millipedes emerge from the soil after a heavy rain and then return there when the desert heat dries the ground exposed to the sun. If millipedes suddenly disappeared from the earth, the bacteria population would thrive and possibly overpopulate. These creatures rely on a dark, damp environment in which to live in (Ibid).
I also found two centipedes, Sclopendra heros (Werner and Olson 100), trying to burrow into the soil. While their slender bodies were tan in color, they were also semi-transparent, allowing me to see some of their internal organs. They typically feed on small insects found under logs, trees, and soil. In doing so, centipedes contribute to the health of their ecosystem by controlling and keeping conditions in balance.
The third organism that I found beneath the ironwood was an Arizona brown spider. This spider's Latin name is Loxosceles arizonica. It is found in the deserts of the American Southwest. It can also be found in potted cholla plants inside people's homes. This spider's diet consists of insects, such as those found in the soil beneath the ironwood I turned over (Preston-Mafham 104). The spider was most likely under the ironwood looking for food and a shady spot away from the desert sun. The Arizona brown spider depends on its environment for the food it requires in order to survive. Like both the centipede and millipede, the Arizona brown spider helps to keep the population of small insects to a minimum.
The fourth species found beneath the ironwood were mound ants, Formica pallide-fulva (Quinn 52). They were scurrying in and out of the anthill they had built. The ant hill serves as protection from predators. The mound ants were gathering small leaves trapped underneath the log. The ant hill serves as protection from predators. These small ants contribute to their ecosystem by eating the decaying leaves from surrounding dead trees.
A second ironwood trunk was found farther south in the same wash. This trunk looked older and was not quite as thick as the first. It also had more branches than the previous tree.
Under the second log were two millipedes trying to crawl back into the soil, much like the ones from the first ironwood. Also under the log was a piece of rattlesnake skin attached to one of the ironwood's branches. About 40 cm from the skin was a hole that looked as if a snake is or was living there. The rattlesnake had shed its skin and a piece of it was snagged on the branch of this tree.
The rattlesnake depends on its environment to provide it with small rodents for food. This snake might have chosen the hole near the tree because the hole was a good spot to find food necessary for its survival.The second trunk I found did not have as many organisms under it, due perhaps to the age difference in the two trees. The first ironwood was younger; therefore, it had more life forms living beneath it. The second ironwood appeared to be older and, as a result, had little organic material to support the food needs of insects and other creatures.
All of theses animals contribute to the health of the desert ecosystem and benefit from it in some way. The food chain is the process connecting them all and maintaining the balance of this delicate environment.
Laughlin, Robin. Backyard Bugs. San Francisco: Chronicle Books, 1996.
Prendergast, Katie. Illustrations. January 1998.
Preston-Mafham, Rod and Ken. The Natural History of Insects. Ramsbury, U.K.: Crowood Press Ltd., 1996.
Quinn, John. Wildlife Survivors: The Flora and Fauna of Tomorrow. Blue Ridge Summit: TAB Books, 1994.
Werner, Floyd and Carl Olson. Insects of the Southwest. Tucson: Fisher Books, 1994.
This winning entry in the museum's Young Naturalist Awards 1998 takes a look at the biodiversity she found in the desert ecosystem of Arizona's Papago Park. Katie's essay with a field journal focus reports on:
Less than 1 period.
Supplement a study of biodiversity with an activity drawn from this winning student essay.