Citation:
Abstract:
Arid and semiarid regions (i.e., deserts) cover about 30% of the world’s continents (except Europe) (Meigs, 1953). Deserts are frequently considered similar ecosystems, with water being the main limiting factor for their biota. This apparent similarity is, however, deceptive. In fact, deserts are extremely varied environments and differ in their climatic and edaphic conditions as well as in their biotic characteristics. Deserts vary in the amount of incident radiation and temperature [e.g., hot (Sahel) vs. cold (Patagonia) deserts], in the amount, frequency, and seasonal distribution of rainfall (e.g., deserts with winter, summer, biseasonal rains, or without seasonal rains), in the composition and geographic origin of their fauna and flora, and so forth. Despite their physical and biological diversification, all deserts are essentially regions of low and irregular rainfall in which évapotranspiration exceeds precipitation. Conditions favorable for plant growth usually occur in specific and rather scattered sites, during relatively short periods of time and sometimes even once in several years. Under such stringent selection, different adaptive strategies have evolved in desert plants, improving their fitness (i.e., individual survival and offspring production) under extreme conditions. These adaptive strategies are combinations of traits from different levels of biological organization and function (e.g., biochemical, physiological, developmental, genetic, demographic). Each of these traits contributes in a balanced and coordinated way to the fitness of the organism (Solbrig, 1993). On the other hand, plants from diverse taxa vary in their adapative potential to xeric conditions due to differences in morphological and physiological characteristics. Moreover, desert species may differ in their life cycle (annuals vs. perennials), life form (shrubs vs. herbaceous forms), timing of flowering, reproductive effort, seed dispersal, germination behavior, and so forth. It is not surprising, therefore, that diverse adaptive strategies are found in different taxa inhabiting deserts with contrasting environments. © 1995 by Marcel Dekker. All rights reserved.