Desert Biomes Evaporation exceeds precipitation. Less than 25 cm of precipitation per year. Low nutrient soil –lack of rain reduces plant growth and decomposition of dead organisms so the soil isn’t very fertile. –Soil is “undeveloped” mostly sand and rock Often found in continent interiors away from oceans and moisture and near mountains. Generally found at or around 30 degrees N and S latitude.

Types of Desert Tropical (Equatorial)– hot year round with little rain. –Often, rain falls within a month or two. EX: Sahara ~25mm in East ~5mm in west Namib ~85mm east ~5mm west Iraq up to 100mm Australian Outback 150mm to 250 mm. Atacama Chile 0.6mm to 2.1 mm Temperate – warm summers, cool to cold winters +/-100mm of rain. Mohave, US and Gobi, China –Mid-latitude deserts – at 30 degrees Sonora, US Polar – cold year round. Dry Valleys, Antarctic, Artic near tundra.

Why do deserts occur where they do? Ocean/Wind currents, Latitude, and Mountains

Rain Shadow Effect

Dry Valleys Antarctica

Temperature doesn’t exceed 10 degrees C and less than 25 cm of precipitation per year.

(Saudi Arabia) Tropical Desert Climatogram

Namib-Naukluft Park, Namibia Welwitschia Tree (Welwitschia mirabilis) 1000 years old.

Grand Erg Desert –Saharan Desert

Temperate desert (Reno, Nevada) Temperate Desert Climatogram

Temperate Desert in Nevada, USA Fig. 5-10b, p. 86

Temperate Desert Arizona

Sonoran Desert scene with Creosote Bush, Saguaro, Cholla, and Paloverde. Credit: © Richard Thom/Visuals Unlimited

Saguaro National Park

Joshua Tree National Park

Red Desert Wyoming this is a “high desert”

Gobi Desert

Fig. 5-10a, p. 86 Roadrunner Producer to primary consumer Primary to secondary consumer Secondary to higher-level consumer All producers and consumers to decomposers Fungi Gambel's quail Red-tailed hawk Collared lizard Jack rabbit Yucca Kangaroo rat Agave Diamondback rattlesnake Darkling beetle Bacteria Prickly pear cactus Temperate Desert Ecosystem

Survival Adaptations of Plants and Animals “Beat the Heat and Every Drop of Water Counts”

Plant Adaptations Wax coatings on leaves to prevent water loss. Deep tap roots to reach ground water Shallow wide spread roots that collect water after brief rainfall. Spongy tissue to store water – succulent Dropping leaves to survive dry spells Dormancy in dry spells Storing biomass in seeds that remain inactive during dry spells. Short life cycles that can be accomplished during rainy season (if there is one).

Sonora desert after rain

Desert Scrub plant community, Mojave Desert - temperate. Cool/Cold winters with about 7 inches of rain, followed by months of drought and extremely hot summers. Yuccas continue to photosynthesize using chlorophyll-containing stems while the leaves of surrounding plants are mostly dried up and dead. - temperate

Cardone cactus in Baja Mexico - Sonoran Desert. Light coloration and vertical orientation help reduce heat uptake. Tall growth places the bulk of the plant above the baking desert floor, and high enough for cooler breezes. Water storage inside the body gives the cactus more control over limited water resources.

Jojoba of the Sonoran Desert. Light colored leaves reduce heat uptake. In addition, the vertical orientation of leaves helps reduce the amount of leaf surface exposed to the sun during the hottest part of the day when the sun is directly overhead.

Animal Adaptations Hiding in burrows and rocky crevices during the day. Nocturnal or Crepuscular (active at dawn/dusk) Thick outer coverings to reduce water loss through evaporation. Dry feces and concentrated urine. Dormancy during extreme periods of drought or heat. Large extremities (big ears, long legs) to help lose heat. No sweating to prevent water loss. Movement…gecko example

Australian Desert Bilby – feeds at night, hides during the day, gets water from the food it eats.

Giant Desert Hairy Scorpion (Hadrurus arizonensis) Arizona. Desert Invertebrates

Thorny Devil a.k.a. Horny Devil (Outback)– lizard that is dormant during the hottest months of the year. Has grooves between it’s scales that lead to its mouth, grooves collect water and can be sucked in by lizard. Slow moving.

Couch’s Spadefoot Toad – spends 8-10 months in hibernation buried in soil until rainy season – emerges, mates, tadpoles develop and then become dormant again.

Desert Predator Prey?

Dromedary camel – long eyelashes, bushy eyebrows, ability to close nostrils against sand, stored fat in hump can be converted to water and energy. Coyote Fennec fox (Africa)

Fig. 5-11, p. 87 Large desert cities Soil destruction by off- road vehicles and urban development Soil sanitization from irrigation Depletion of underground water supplies Land disturbance and pollution from mineral extraction Storage of toxic and radioactive wastes Large arrays of solar cells and solar collectors used to produce electricity Major Human Impacts on Deserts

Future?