Hot Deserts

AbstractHot deserts occur in two global belts north and south of the equator, at latitudes where calm air and a stable atmosphere dominate. Desert rainfall occurs in the form of highly unpredictable pulses followed by long periods of drought, and many plants and animals are finely adapted to these cycles of abundance and scarcity. Water‐storing succulents and short‐lived ephemeral plants are some of the most common life forms in these highly variable and strongly pulsating environments. In spite of their apparent barrenness, the hot deserts of the world harbour unique and rare biotas with impressive biological adaptations. As a result of evolution in isolation from each other, the world's deserts have high levels of endemism and harbour rare and unique life forms, a fact that makes them ecologically fragile and highly vulnerable to biological extinction.Key Concepts:Large deserts occur in the mid‐latitudes of the world, north and south of the equator, where the atmosphere is highly stable and calm air dominates.Smaller rain shadow deserts often develop in the leeward side of mountain ranges, which capture moisture before it reaches the downwind side.Coastal fog deserts, such as Atacama or the Namib, owe their aridity to cold ocean currents, and their moisture oscillates with oceanic ‘El Niño’ cycles.A panoply of morphological and physiological adaptations have evolved in desert environments, which allow plants and animals to survive the harsh desert conditions.Some plants store water in fleshy tissues, others develop extremely long roots to tap water in the deep soil aquifer, while others simply die as the drought sets‐in and survive long periods in the form of seed.Animals may migrate into areas where rain has fallen, and have a complex set of morphological and physiological traits that allows them to regulate their temperature without losing water.The harsh conditions of deserts have promoted the evolution of a complex set of positive relations among desert organisms, such as ‘nurse’ plants, and elaborate pollination and seed dispersal interactions.