Lessons On the Lake

Lesson Plan
Lessons On the Lake
Amistad National Recreation Area
by Lisa Evans
Education Specialist, Amistad NRA

Amistad National Recreation Area and Del Rio, Texas are on the edge of the Chihuahuan Desert. While the Chihuahuan Desert extends into West Texas and New Mexico, most of it lies in Mexico.

What is a desert? As different from one another as deserts of the world are, they all share one characteristic - they are very dry. Some scientists define deserts as areas that get less than 10 inches of rainfall a year. Deserts are a very special type of habitat and it may surprise you to learn that many different kinds of plants and animals live in them. Desert plants have special ways of dealing with heat and other desert conditions. Desert animals have adaptations that help them deal with two desert problems: scarce water supplies and high temperatures.

Desert Plants

Because of the habitat in which they live, desert plants have special ways of dealing with heat and dryness. These plants are very different from plants that grow in other (non-desert) areas. Most plants, including desert plants, carry out the process of photosynthesis. Plants absorb carbon dioxide from the air and release oxygen. In order to do this, small pores (called stomata) on a plant's leaves and stems must open. Each time the stomata open, some water is lost. This water-loss process is called transpiration. For most non-desert plants, losing a lot of water through transpiration is not a problem because they can replace the water by sucking up more moisture through their roots. But, desert plants can not afford to lose a lot of water through transpiration - it's much harder for desert plants to replace lost water.

Some transpiration "tricks" to save water:

· Smaller, fewer pores (stomata)
· A waxy cover
· Pores open at night - not during heat of day
· Small leaves or none at all
· Hide from the sun - expose as little to the sun as possible
· Drop their leaves during drought
Other water-saving adaptations of desert plants:

· Some desert trees and shrubs grow very deep tap roots
(some can be 100 feet long!)
· Many cactuses and shrubs grow very shallow roots that spread out from the plant in all directions. These shallow roots can quickly absorb any rain that falls.
· Some desert plants have pleats or "folds" that allow them to swell with water after a rainstorm. These pleats or folds allow desert plants to store the much needed water.
· Hairs and spines on cactuses and other desert plants help to break the wind - this helps to keep the plants from drying out. These hairs and spines also provide shade for the plants. Spines also protect the plants from hungry animals.

Desert Animals

Animals that live in the desert have some very difficult conditions to deal with - not much water and high temperatures. Some desert animals can actually go through life without ever taking a drink of water. How do they do it? Or, imagine living in a place where summer temperatures can go over 120 F. (with no air conditioning!). Desert animals have some very important adaptations that enable them to live in the desert. These include:

· Water from food - some desert animals, such as pack rats can get all of the water that they need by eating juicy cactuses and other plants that have lots of water in them. Some snakes can get all of the moisture that they need from the mice and other small animals that they eat.
· Move to water - large desert animals, such as mountain lions or deer, can get some of the water that they need from the food they eat. But, in order to get all of their needed water, these animals must also drink water, too. To find sources of water, these larger desert animals may have to travel great distances.
· Sleeping through the tough times - some desert animals deal with the hot, dry times (droughts) by "sleeping" through it.
Just as some non-desert animals hibernate through the cold winter, some desert animals estivate through the dry periods. Spadefoot toads can wait out dry periods underground for months and even years. They are covered with a jellylike substance that keeps them moist while they are waiting for rain.
Some desert rodents, snails and spiders "sleep" through the hottest, driest times of the year. By estivating, animals can avoid not only hot, dry conditions but also a food shortage.
· Staying out of the sun - many desert animals avoid the daytime heat by being nocturnal (active at night). Some animals are active only during the early morning and late afternoon (cooler times of the day). During the heat of the day, when ground temperatures can reach 160 F., lizards, snakes, insects and other animals will get out of the heat - digging into the ground, going into other holes, crawling under rocks, looking for shade under bushes and trees, etc. Some birds, such as vultures, will fly higher into the sky, where temperatures are cooler.
· Big ears and long legs - big ears help to cool down their owners by radiating heat out of the animal's body. Like big ears, long legs also radiate body heat. And, long legs keep vital internal organs away from the hot ground. Some insects and lizards keep their insides cooler by straightening out their legs as they walk across the hot ground.

People of the Lower Pecos Area

The people of the Lower Pecos area lived here for over 9,000 years. They were hunter-gatherers and lived in bands of 25 - 30 people (mothers, fathers, children, aunts, uncles, close relatives). These Indian bands lived on what nature provided and continually adapted to their environment. How do we know that they were here? Well, over time, they left behind quite an assortment of everyday items as well as many examples of rock art. In the dry rock shelters of this area, items such as mats, nets, sandals, knives, baskets, arrowheads, fishing hooks, etc. were preserved and have been found. Also found in the rock shelters of the Lower Pecos area are many panels of rock art, called pictographs. Some of the rock art was painted as long ago as 4,000 years before present time. There are several different styles of rock art. Another form of rock art has been found in this area - they are referred to as painted pebbles. Flat limestone rocks were used in this type of rock art. The rocks were painted with abstract linear designs. The people of the Lower Pecos area disappeared in the early 1700's. They may have joined other Indian tribes (like the Apaches), gone to northern Mexico, or joined the Spanish missions.

AMISTAD BINGO

In order to help prepare the children for the Amistad Bingo activity on the nature trail and the other planned learning activities, you may want to utilize the provided information (found on the "Lessons From the Lake" pages).

The information included on the "Amistad Bingo" pages will apply mainly to the nature trail "bingo" activity. However, the children will also learn some of the same information at the other activity stations.

Something made by Ancient Texans - the people of the Lower Pecos Area lived here for over 9,000 years. We know that they were here because they left behind such things as arrowheads, baskets, sandals, nets, knives, etc.

Place for an animal to get out of the sun - one of the problems that desert animals face is the hot sun and high temperatures. One way to deal with this problem is to get out of the sun. Animals may go down into a hole, crawl under rocks, find shade under a bush, etc. Some birds, such as vultures, will fly high into the sky where it is cooler.

An animal home - animals use a variety of shelters for homes. These might include a nest in a tree or even in a cactus, a hole in the ground, a rock shelter, etc.

Fossils - evidence of prehistoric life. Fossils may be the remains of plants or animals (fossilized bones and teeth) or even the tracks left by dinosaurs.

A plant that swells to store water - some cactuses, such as the barrel cactus have folds or pleats that allow them to expand so that they can store water after a rain.

Painted pebbles - one of the forms of rock art that was left behind by the people of the Lower Pecos. The painted pebbles are flat limestone rocks that have abstract designs painted on them.

Pictographs - the main form of rock art done by the people who lived in this area long ago. There are different styles of pictographs found in the rock shelters. Red, black, yellow, orange and white paints (made from ochres, clays, minerals, etc.) were used in these pictographs.

Desert grasses - grow in many parts of the Chihuahuan Desert. These grasses provide food for deer, rodents and other plant-eaters. Many of the desert grasses will "roll or curl up" during the day to protect themselves from the sun.

Sign that an animal was here - If you look around outdoors, there are many signs that an animal was in the area - these "signs" could include their tracks left in the dirt or mud, bones, a spider web, animal scat or "poop", or even a prickly pear cactus that has had some bites taken out of it.

Something that you can do at Lake Amistad - Amistad National Recreation Area includes 57,292 acres; 540 miles of United States shoreline; 67,000 acres of water (when the lake is full). People can go boating, fishing, swimming and scuba diving at Lake Amistad. Visitors also camp out, picnic and hike at Amistad National Recreation Area.

A "bad" sign that people were here - one of the "bad" signs that people were here is litter. We ask that people take their trash with them or put it into one of the trash cans found in the area.

Prickly pear cactus - one of the most common cactuses in the Chihuahuan Desert. The flattened pads of the prickly pear are one of its adaptations to living in the desert - not as much sun can shine on the pads that are flattened laterally. Prickly pear is a source of food for many desert animals, including the javelina (or collared peccary). It is also a source of water - the prickly pear can store water in its pads after a rain.

Yucca - There are a number of different species of yucca that grow in the Chihuahuan Desert. The one that we will look at on the nature trail is the Torrey Yucca or Spanish Dagger. Yuccas were very important to the early Native American people of this area -- they used the fibers from the leaves to make mats, baskets, sandals, carrying bags, and paintbrushes. The yucca was also used for food - flower buds and fruits were eaten raw or cooked and the "heart" of the yucca was cooked in an underground pit for two days and then eaten.

Sotol - The long woody flower stalk of sotol has been used in West Texas and Mexico to construct temporary shelters, corrals, and other structures. The "heart" or leaf base was cooked in an underground pit by Native Americans who lived in this area. The narrow, tough leaves were used to weave baskets, mats, and other items.

Lechugilla -- is the indicator plant of the Chihuahuan Desert. Lechugilla grows no where else in the world - just the Chihuahuan Desert. Native Americans of this area used the lechugilla as a source of fibers, food, medicine, drink, and soap. Lechugilla is the source of hard fibers, called "istle" which is used for rope, twine, and other materials.

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