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Exhibits: Desert Grassland

At our Desert Grassland exhibit you will be surrounded by native grasses and animals that are found in desert grasslands. You can observe the antics of our ever popular prairie dogs, see a replica of a mammoth kill site, and stroll through towering soap tree yuccas.

Grassland is a semiarid biome characterized by warm, humid summers with moderate rain and cold, dry winters. (The central valley of California is an exception; it is a winter-rainfall grassland at a lower than typical elevation.) Grass is the dominant life form; scores of species form a nearly continuous cover over large areas. Other well-represented life forms are annuals and geophytes (herbaceous perennials such as bulbs that die to the ground each year). Populations of trees, shrubs, and succulents are kept at low levels by periodic fires during the dry season.

Most of the grasslands in the western states are intermediate between the true prairies of the American Midwest and deserts. They are called semi-desert or desert grasslands. Compared with prairie grassland, the grasses in desert grassland are shorter, less dense, and are more frequently interspersed with desert shrubs and succulents. Desert grassland or chaparral borders the northern Sonoran Desert on the east.

Currently on exhibit in our Desert Grassland:

Black-tailed Prairie DogGreat Blue Heron

Black-tailed Prairie Dog

Nowhere else can you see this sight: black-tailed prairie dogs in an Arizona grassland. Once numerous over their small range in this state, now they're completely gone. Black-tailed prairie dogs (one of five prairie dog species) still live elsewhere in the western United States and in Mexico.

Prairie dogs are grassland squirrels. They eat vegetation, mostly grass, which is 70 - 90% of their diet.

Black-tailed prairie dogs do not hibernate, but may stay underground in bad weather. Prairie dog predators are eagles, hawks, bobcats, rattlesnakes, coyotes, badgers (and at one time, the black-footed ferret, which specialized in prairie dogs and is also now gone from Arizona).

Generally loved for their antics, prairie dogs are hated by some people and have been exterminated because they were thought to compete with livestock for food. The degree of competition is difficult to determine and is still under investigation.

Sonoran green toad (Bufo retiformis)

The Sonoran green toad is small, reaching only 2½ inches (57 mm) in length. Brightly colored, this toad is green to greenish-yellow with reticulations (net-like lines) or spots of black or brown on the back and legs, and numerous small, black-tipped warts on the back and sides. The underside is white with an occasional speck or two of black. The parotoid glands are large. Males have a dark throat.

Once the summer rains begin, males move into grasses around temporary rainwater pools and washes and begin to call. The call lasts a few seconds and sounds like a combination buzz and whistle. Hatchlings are only 1/8 inch (3.5mm) in length-smaller than a pea!

Termites

Termites are morphologically uncomplicated insects, in contrast with their astonishingly complex social behavior. Superficially termites resemble and are sometimes mistaken for ants, which also exhibit social behavior. Sonoran Desert termites range in size from 4 to 11 mm (1/8 - 7/16 inches) long, not including the wings of alates (the winged reproductive adult forms that appear occasionally, especially during and following rains). Workers are white with small head capsules. Soldiers have enlarged head capsules, and very formidable jaws, or in one of our species, a snout-like structure.

This highly successful group of social insects plays an essential ecological role in the decomposition and recycling of a nutritionally poor, highly resistant, but extremely abundant substance: cellulose. Cellulose is a poly-saccharide, that is, a large number of sugar molecules linked together by tight chemical bonds to form a very long, strong chain. Cellulose is the substance that gives plants their structure and is the most abundant organic compound in the world. Wood is mostly cellulose, and so are cotton and all paper products. In the Sonoran Desert, trees, shrubs, grasses, and cactus skeletons are the primary source of cellulose, which represents more than half of all the organic material produced by photosynthesis. Cellulose is durable because it is a physically strong material resistant to mechanical breakdown, but more important, very few organisms produce enzymes that can chemically break it down. Among those that do produce the cellulose break-down enzyme cellulase are fungi and tiny animals called protozoans. Termites do not produce cellulase, but all termites contain protozoans in their guts in a mutually beneficial relationship known as mutualism. Termites grind up the cellulose mechanically by biting off bits and chewing them up; then the protozoans in their guts break down the chewed mass into sugars, which are readily absorbed through the termites' guts. Both the termites and their protozoans share in the nutritional benefit of these released sugars. Newly hatched termites are first inoculated with these indispensable protozoans by eating the feces of their older brothers and sisters.

The ecological importance of Sonoran Desert termites can best be understood by considering the following question: What would happen if we didn't have termites in our desert? Well, because our aridity severely limits the abundance and distribution of wood decaying fungi, without termites, we would soon be neck deep in cellulose in the form of mesquite and palo verde wood, dead grasses, cactus skeletons and dung. Eventually, few living plants would be left to produce food for animals because there would be no space for new plant seedlings to establish and no nutrients to sustain their growth. All of the space would be taken up by dry, un-recycled cellulose litter, and all of the nutrients would be tied up in this material and thus unavailable for plants in the soil. Without plants fixing carbon-producing food, most animals would disappear. So, without termites, the whole desert ecosystem as we know it would simply collapse.