Fairly extensive hot deserts also occur in India (Sind-Rajasthan deserts), South America and North America and Australia. The cold deserts occur at elevations where the temperatures are low and rainfall scanty as the air losses all its moisture content as it ascends higher and higher.
Cold deserts occur in Ladakh regions of Himalayas, Tibet, and Bolivia Arctic. The hot and cold deserts may also be distinguished by differences in plant population which are mostly succulent type (e.g., cactus, palavered trees, creosote bush, etc.). Most cold deserts have sage bush.
Low erratic precipitation coupled with soil and air temperatures that are extremely high by day and drop abruptly by night, low humidity, and high insulation are the major desiccating environmental factors to which desert vegetation and animals have adapted.
Dessert plants which tend to be shrubs are adapted to drought conditions through reduced leaf size and the dropping of leaves in dry conditions, both reducing water loss via evapotranspiration. The of most desert plants remain well developed and occur in the top?
Meter of the soil to take maximum possible advantage of any rainfall further, the root hairs on many desert plants are ephemeral, drying back under drought conditions and thereby reducing potential water loss by osmosis.
Yet other species are short lived annuals that complete their life cycles during the short-moist period. In most hot deserts, there occur plants such as cacti, water-storing succulents such as acacias, euphorbia’s, cacti, prickly pears, etc., which are adapted by their protoplasmic colloids, which enable the accumulation of substantial water reserves, as well as by a reduced leaf surface, which obviates water loss via evapotranspiration.
The animals present in the desert are reptiles, insects and burrowing rodents. All these animals possess special morphological, physiological and ethological adaptations for deserts.
In general, large animals are very uncommon except mule, deer and some species of gazelle and all animals have cursorial, fossorial and or salutatorian adaptations. Some desert animas are nicely adapted for high extremes of temperature.
For example, the lethal the temperature for different species of insects found to be following—for the canal spider Galeodcs granti it is 50°C, for the Gryllus domestics it is 40°C and for the forficulid Labi dura riparia it is 38 C (Cloudsely-Thomp- son, 1962).
Diurnal rhythms are perhaps the best method of avoiding the heat. While some desert plants close their petals at night, many blossom only at night. Some insects like tenebrionid bettle Akis spinosa remain active during the day, and the centipede Scolo- pendra clavipes restricts its activities to night time.
Further, certain reptiles and certain insects are well adapted for survival in deserts because of their thick, impervious integuments and the fact they excrete dry waste matter. A few species of mammals have become secondarily adapted to the desert by excreting very concentrated urine.
They avoid the sun by remaining in their burrows during the day. Kangaroo rat and pocket mouse, both are able to live without drinking water by extracting the moisture from the seeds and succulent cactus they eat.
The camel and the desert birds (Ostrich, etc.) must have an occasional drink of water but can go for long periods of time using the water stored in the body. Most insects of deserts are herbivores and as a correlation the number of small insectivorous lizards found in the desert is usually high.
Fauna of Indian deserts. Prakash (1974) have recognized four habitat types in the Indian desert based on land forms namely aquatic, sandy, rocky and, riparian habitat (river banks).
The aquatic habitats of Indian deserts which remain confined to the perennial lakes, are inhabited by various species of fishes like Labeo nigripinnis, Oxygaster clupeoides, Tor khurdee, Puntius amphibia, Neomacheiius denisonii. Among amphibians of the Indian desert are a species of toad (Bufo andersonii) and five species frogs (Indian bull frog Rana tigrina, cricket frog Rana limnocharis and burrowing frog Rana breviceps being dominant species).
Among reptiles, there occur one species of crocodile (Crocodilus palustris), two species of testudines (Loricata), 18 species of lizards and 18 species of snakes. Of the lizards, some species like Acanthodactvlus cantoris, Calotes versicolor, Uromastix hara’wicki, Ophiomorus tridactylus are predatory on the desert locust inhabiting localized areas in the Thar Desert.
The avian fauna of the Indian desert includes species like painted partridge Francolinus pictus pallidus, grey partidge Francolinus pondicerianus, grey quail Coturnix, black breasted or rain quail Coturnix coro- mandelicus, rock bush quail, the little bustard quails Lurnlx sylvatica, button quail Turnix tanki, great Indian bustard Choriotes nigriceps, florican Sypheotides indica, Indian sand grouses like Petrccles exustus erlangeri, Petrocles alchata, P. senegallus, and P. indices. During winter numerous aquatic birds become abundant in Indian deserts.
Such birds are white fronted goose Anser albifrons, wigeon Anas penefope, garganey Anas querguedrila, red crested pochard Netta fufina and tufted duck Aythya futigola. Among the predominant predatory birds are two species of the vultures namely Gyps bengalensis and the white vulture Neophron perenopterus.
The mammalian fauna of India deserts includes many species, some of which have been tabulated in the following table:
All these mammals have well specialized adaptations for survival in thermal extremes and low humidity. Many of them possess diurnal rhythmic activities.