Desert By Miriam Khan Chiyeung Lau Charles Song

Desert By: Miriam Khan Chiyeung Lau Charles Song Alexander. Kalogerou

What is the desert?

A desert is a region that receives very little precipitation. Deserts can be defined as areas that receive an average annual precipitation of less than 250 mm (10 in), or as areas in which more water is lost than falls as precipitation. The desert gets up to 131 degrees F or 55 degrees C during the day. During the night, the temperature drops near freezing.

Where is it located in the biosphere?

§ Many deserts are located between the tropic of cancer and the tropic of capricorn. 30 degrees north latitude. 30 degrees south. Located in every continent. § Deserts sometimes contain valuable mineral deposits that were formed in the arid environment or that were exposed by erosion. Due to extreme and consistent dryness, some deserts are ideal places for natural preservation of artifacts and fossils.

Deserts are located in every continent. Africa- Sahara, Kalahari Antarctica- interior of the continent is the world’s largest desert. Asia- Gobi, Kara Kum Australia- Gibson, Simpson Europe- Accona, Halendi North America- Mojave, Sonoran South America- Atacama, Monte

Abiotic and Biotic Factors Of The Desert What are they?

Abiotic Factors

§ Abiotic Factors are non-living physical and chemical factors which affect the ability of organisms to survive and reproduce. § Abiotic factors vary in the environment and. the types and numbers of organisms that exist in that environment. § Limiting factors determine the types and numbers of organisms in a ecosystem. Many limiting factors restrict the growth of populations in nature. § In hot and dry Deserts the rainfall is usually very small. Sometime rain evaporates before it hits the ground. Sometimes it rains up to 28 CM and sometimes it never rains.

§ Soils are course-textured, shallow, rocky or gravely with good drainage and have no subsurface water § The seasons are generally warm throughout the year and very hot in the summer § Temperatures exhibit daily extremes because the atmosphere contains little humidity to block the Sun’s rays. Desert surfaces receive a little more than twice the solar radiation received by humid regions and lose almost twice as much heat at night. Many mean annual temperatures range from 20 -25° C. § In Semiarid Deserts The summers are moderately long and dry, and like hot deserts, the winters normally bring low concentrations of rainfall. Summer temperatures usually average between 21 -27° C. .

§ The soil can range from sandy and fine-textured to loose rock fragments, gravel or sand. There is no subsurface water. § As in the hot desert, rainfall is often very low and/or concentrated. The average rain fall is 2 -4 cm annually § Coastal Deserts are moderately in cool to warm areas. The average temperature ranges from 5 - 24 C. § The average rainfall measures 8 -13 cm in most areas. § The soil is fine-textured with a moderate salt content. It is fairly porous with good drainage.

§ Cold Deserts are characterized by cold winters with snowfall and high overall rainfall throughout the winter and occasionally over the summer. . § The temperature range is between -2? to 26° C. § The winters receive snow. The mean annual precipitation ranges from 15 -26 cm. § The heaviest rainfall is usually in April or May. § The soil is heavy, silty, and salty.

Biotic Factors

§ Biotic Factors are all the living things or their materials that directly or indirectly affect an organism in its environment. This includes organisms, their presence, parts, interaction, and wastes. Factors such as parasitism, disease, and predation (one animal eating another) would also be classified as biotic factors. § Carrying Capacity is the maximum number of organisms the resources of an ecosystem can support. The carrying capacity of the environment is limited by the available abiotic and biotic resources (limiting factors), as well as the ability of ecosystems to recycle the residue of dead organisms through the activities of bacteria and fungi.

§ In the Hot and Dry Desert , Plants are mainly ground-hugging shrubs and short woody trees. In the cacti, the leaves are muchreduced to spines and photosynthetic activity is restricted to the stems. These plants include: yuccas, ocotillo, turpentine bush, prickly pears, false mesquite, sotol, ephedras, agaves and brittlebush. § The animals include small nocturnal (active at night) carnivores. The dominant animals are burrowers and kangaroo rats. There also insects, arachnids, reptiles and birds. The animals stay inactive in protected hideaways during the hot day and come out to forage at dusk, dawn or at night, when the desert is cooler.

§ Many plants in the Semiarid Desert have silvery or glossy leaves, allowing them to reflect more radiant energy. Semiarid plants include: Creosote bush, bur sage, white thorn, cat claw, mesquite, brittle bushes, lyciums, and jujube. § Many animals find protection in underground burrows where they are insulated from heat. These animals include mammals such as the kangaroo rats, rabbits, and skunks; insects like grasshoppers and ants; reptiles are represented by lizards and snakes; and birds such as burrowing owls and the California thrasher. § In the Coastal Desert Some plants have extensive root systems close to the surface where they can take advantage of any rain showers. All of the plants with thick and fleshy leaves or stems can take in large quantities of water. The plants living in this type of desert include the salt bush, buckwheat bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus.

§ Some animals have specialized adaptations for dealing with the desert heat and lack of water. Some toads seal themselves in burrows with gelatinous secretions and remain inactive for eight or nine months until a heavy rain occurs. Amphibians that pass through larval stages have accelerated life cycles, which improves their chances of reaching maturity before the waters evaporate. § Some insects lay eggs that remain dormant until the environmental conditions are suitable for hatching. The fairy shrimps also lay dormant eggs. Other animals include: insects, mammals (coyote and badger), amphibians (toads), birds (great horned owl, golden eagle and the bald eagle), and reptiles.

The Food Web What is it?

A food chain is sequence of plants, herbivores and carnivores, through which energy and materials move within an ecosystem. Food chains are usually short and not more than three or four links. They usually consist of a producer, a consumer and a predator, with the predator being the top of the food chain. The top of the desert food chain does eventually die though, and is returned to the bottom of the chain as nutrients by decomposers.

The pyramid consists of three main groups. The first one(bottom) are the primary producers. Second(middle) are secondary consumers. And the third(top) are primary consumers.

Primary producers § These are plants that make food through photosynthesis. Limited by the availability of water, they produce fewer than 200 Kilocalories of food for the animals for each square meter each year. Including: Trees, shrubs, cactus, wildflowers, grasses.

Secondary consumers These animals are usually small and eat little. Many are insects, small mammals, or reptiles. They eat plants or the herbivores that eat the plants. As food for larger predators, they provide about 20 Kilocalories per square meter per year for predators.

Primary consumers § they are the top predators. They eat the secondary consumers. In the desert they would consist of big birds like hawks, coyotes, and other bigger animals.

Arctic Desert

This is the opposite of a dry desert. These consist of large amounts of snow. Most of the area is surrounded by the ocean. Many of the biotic factors of this environment come from the ocean. The killer whale is the top of the chain in the ocean. They hunt smaller animals like seal fish and penguin. They eat smaller fish, phytoplankton, etc.

§ The Arctic is a cold desert because it gets very little precipitation but it so cold that the snow that does fall doesn't melt, so deep snow covers the land ice. § As long as there is some source of moisture and some way to lift or cool the air, it can snow even at incredibly cold temperature. However, most heavy snowfalls occur at temperatures just below freezing (15°F/-10°C or warmer) since warmer air can hold more water vapor. § The very cold Arctic air is not able to hold much moisture, and therefore it doesn't rain or snow very often - and that makes it a desert.

Typical Biomass Pyramid

What’s an Oasis?

§ an oasis is an isolated area of vegetation in a desert, surrounding a spring or similar water source. Oases can provide habitats for animals and even humans. § People who live in an oasis use every bit of land. Water has to be used carefully; the fields must be irrigated to grow plants like dates, figs, olives, and apricots. § The most important plant in an oasis is the date palm which forms the upper layer. These palm trees provide shade for smaller trees like peach trees, which form the middle layer. The date palms do more than protect other plants from the burning sun - all parts of an oasis are very important for the people. And also growing plants in different layers, the farmers make best use of the soil and water.

Desertification

§ Deserts take up 1/3 of earth’s land mass. § Desertification takes place in dryland areas where the earth is especially fragile, where rainfall is nil and the climate harsh. The result is the destruction of topsoil followed by loss of the land's ability to sustain crops, livestock or human activity. The economic impact is horrendous, with a loss of more than $40 billion per year in agricultural goods and an increase in agricultural prices.

§ Some deserts located by mountains and are caused by the "rainshadow" effect. As air moves up over a mountain range, it gets cold and loses the ability to hold moisture so it rains or snows. When the air moves down the other side of the mountain, it gets warmer. Warm air can hold lots of moisture, so it doesn't rain as much.

Climatic changes can trigger the desertification process, but human activities frequently are the proximate cause. Over cultivation exhausts the soil. Deforestation removes trees that hold the soil to the land. Overgrazing of livestock strips the land of grasses. According to a UN study, about 30% of earth's land - including the 70% of dryland - is affected by drought. Every day, about 33, 000 people starve to death.

Desertification creates conditions that intensify wildfires and stirring winds, adding to the tremendous pressure to earth's most precious resource, water, and, of course, the animals dependant on it. According to the World Wide Fund for Nature, the world lost about 30% of its natural wealth between 1970 and 1995.

§ Dust from deserts and drylands is blown into cities around the world. Dust from Africa reaches Europe through the Pasat wind, and even reaches US cities. Dust particles, which are less than 2, 5 millionths of a metre in size, are inhaled, causing health problems and have been shown to boost death rates.

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