Saguaro cactus is poisonous
Sonora: And the desert lives forever
If the Sonora is a desert, why does the vegetation grow so dense here in many places that you can hardly walk through it without tearing your skin on the thorns of the plants? If the glow of the sun practically extinguishes all life, where do all the animal tracks in the sand come from? Those of the collar peccaries, the mule deer or the cat frets. And those of the rodents, which are so numerous that the hundred or so rattlesnakes per square kilometer do not hunt to get food, but just lie there and wait? Presumably, this ecosystem just needs better public relations.
It's true: the Sonora desert is drying up and getting hotter and hotter. But their landmark, the saguaro cactus with its arms protruding upwards, is not a perch for vultures in a dead wasteland. On the contrary: the columnar plants are living water reservoirs. If it has rained, most of them form new root fibers within a few hours in order to bind as much moisture as possible. The tissue structure of the cacti resembles an accordion. When the plant soaks up liquid, it folds up.
In May and June, the driest months, the saguaro and its even larger southern counterpart, the Cardón candelabra cactus, crown each other with striking white flowers. With their nectar, they provide food for birds, insects and, above all, bats. In return, they are pollinated. Juicy fruits emerge from the flowers, which provide food and moisture for an even greater number of living things such as iguanas and kit foxes until the summer thunderstorms set in. To rest and digest, the animals retreat under one of the many small trees and shrubs typical of the desert, such as the desert ironwood Olneya tesota or the honey mesquite Prosopis glandulosa. The animals leave their excrement containing seeds exactly where a saguaro or cardón spends its youth: in the shade of a nurse plant. So if all life here hangs by a thread, how is it that a saguaro produces millions of seeds year after year and can live up to 250 years?
The shady strip on the edge of the arroyo - Spanish for "watercourse", here: a dry river bed - is a good place to rest. Shortly before that, a July downpour had brought two and a half centimeters of rain down on Saguaro National Park in Arizona. The water still seeps into the arroyo and gathers in small pools that serve as drinking troughs for carolin pigeons, cactus wrens and hundreds of bees. And somehow tadpoles have also found themselves in the water pits between the rocky mountain slopes. Native American Indians who stopped here a long time ago have left drawings of people and ghosts on the stone walls. It almost seems as if the figures are on guard. You have seen the struggle for survival that is about to take place here many times.
Many frogs and toads take months to develop from egg to adulthood. Garlic toads are similar to real toads, but with smoother skin, feline eyes, teeth, and a heel hump on their hind feet. And they follow different rules. Adult animals live in a twilight state on the desert floor until they feel the vibrations of thunder and raindrops. Then they come out and gather at the pools. They fill the night with deafening choirs and mate. The offspring has an accelerated metabolism. The tadpoles grow into young toads within just eight days.
Now the race against time has begun: you have to jump around and fatten yourself up with insects before the arroyo dries up again. The amphibians with their moist skin have no choice but to bury themselves again and wait for the next heavy rainfall. This can take months - but also longer than a year. If red-spotted toads have spawned in an arroyo, which are usually found at more permanent water sources, then the tadpoles are lost. If it was shovel-foot toads, they have a chance. Every day they grow a little more. Every day the pools shrink and evaporate in the midday sun.
This fight also affects the Gila crustacean. “A year ago she was near death. Just skin and bones. She was always looking for food, but there was nothing, ”says Jon Davis, who studies at Arizona State University. For three years he followed the lizards with the help of implanted transmitters and tiny temperature recorders. In the light of our headlamps, he grabs a 38 centimeter long specimen behind the lower jaw. The animal hangs in the air like a toy kite adorned with pink and black pearl embroidery. It has a big belly and the wriggling tail is as plump as a sausage. The fur from a baby rabbit sticks to its mouth. This reptile is clearly doing better. Davis removes a couple of cactus thorns from the animal's toes and puts it in a pocket for a closer look in daylight. The following morning he examines it - it's a female - with a portable ultrasound machine. It would be wise to have a cup of coffee before doing such work in order to be as attentive as possible. Because the Gila-Krusty Lizard and its closest relative, the Scorpion-Krusty Lizard, are poisonous. Their bites cause severe pain, dizziness, and worse. The animal's bladder appears on the screen. It contains a large amount of water - in the currency of the desert ecosystem: a fortune. "Gila lizards can drink so much water in a day that their body weight increases by 20 percent," says Davis.
Sonora covers an area of around 260,000 square kilometers and includes the southeastern tip of California, southwest Arizona, around half of the Mexican state of Sonora and almost the entire Baja California peninsula. In some parts of the desert there is only three inches of precipitation per year. In others, however, there are 25 to 30 centimeters. The storms approaching from the Pacific in winter usually provide half of the annual rainfall. The winters of 2004 and 2005 brought record rainfall that ended a multi-year drought. The following spring, the region glowed and smelled like a florist's fair. Even plants that had disappeared for decades sprouted from patient seeds.
Then came summer. In Tucson, the temperature rose to at least 38 degrees for 39 consecutive days. Sonora is the deepest and hottest of the four great deserts in North America (next to the Mojave and Chihuahua Deserts and the Great Basin). It is also the only one with two clearly distinguishable rainy seasons. The summer heat rising over the land draws moist air from the Gulf of California and the occasional Gulf of Mexico. In the afternoon, thunderclouds often spread across the scorching sky and bring heavy rainfall that causes sudden floods. When these monsoon weather arrives, they trigger a new plant growth cycle.
This in turn results in higher birth rates in rabbits, rodents and birds, whose young are among the favorite foods of the Gila crustacean. Sometimes she eats so much on a nest that her weight increases by half. Then she retires to her den for a week or more. A hormone that was only recently discovered in the lizard's poisonous saliva apparently supports the regulation of this cyclical activity behavior. In 2005, a synthetic version of the chemical was approved as a drug. It has been shown to be very effective in treating type 2 diabetes and could also help patients lose weight at the same time.
Read the entire article in the 09/2010 issue or in the current iPad app.
(NG, issue 9/2010, page (s) 64)
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