Deserts have less than 25 centimeters of precipitation annually, but otherwise vary greatly, depending on elevation and latitude. Many deserts undergo extreme daily temperature changes, alternating between hot and cold.
Abiotic factors low precipitation; variable temperatures; soils rich in minerals but poor in organic material
Biotic factors
Plant life: Many plants, including cacti, store water in their tissues, and minimize leaf surface area to cut down on water loss. Cactus spines are actually modified leaves. Many desert plants employ special forms of photosynthesis that enable them to open their leaf pores only at night, allowing them to conserve moisture on hot, dry days.
Animal life: Many desert animals get the water they need from the food they eat. To avoid the hottest parts of the day, many are nocturnal—active only at night. Large or elongated ears and other extremities are often supplied with many blood vessels close to the surface. These help the animal lose body heat and regulate body temperature.
Plains and prairies, underlain by fertile soils, once covered vast areas of the midwestern and central United States. Periodic fires and heavy grazing by herbivores maintained plant communities dominated by grasses. Today, most have been converted for agriculture because their soil is so rich in nutrients and is ideal for growing crops.
Abiotic factors warm to hot summers; cold winters; moderate seasonal precipitation; fertile soils; occasional fires
Biotic factors
Plant life: Grassland plants—especially grasses, which grow from their base—are resistant to grazing and fire. Dispersal of seeds by wind is common in this open environment. The root structure and growth habit of native grassland plants helps establish and retain deep, rich, fertile topsoil.
Animal life: Because temperate grasslands are such open, exposed environments, predation is a constant threat for smaller animals. Camouflage and burrowing are two common protective adaptations.
In open woodlands, large areas of grasses and wildflowers such as poppies are interspersed with oak and other trees. Communities that are more shrubland than forest are known as chaparral. Dense low plants that contain flammable oils make fire a constant threat.
Abiotic factors hot dry summers; cool moist winters; thin, nutrient-poor soils; periodic fires
Biotic factors
Plant life: Plants in this biome have adaptated to drought. Woody chaparral plants have tough waxy leaves that resist water loss. Fire resistance is also important, although the seeds of some plants need fire to germinate.
Animal life: Animals tend to be browsers—meaning they eat varied diets of grasses, leaves, shrubs, and other vegetation. In exposed shrubland, camouflage is common.