Summary of the Complementary Sets of Survival Strategies of Some Common Species of the Negev Desert That Have Been Studied in Detail

Abstract

Under extreme desert conditions, there are cardinal environmental factors (Chap. 1) that have pronounced influences on the evolution of many complementary sets of adaptations. Ephemeral plant species of unrelated taxa in the Negev Desert of Israel have developed complementary sets of adaptation and survival strategies as ecological equivalents having physiological, morphological, phenological and anatomical resemblances (Cloudsley-Thompson 1996, 2001) in the various stages of their life cycles (Chaps. 2–7). The adaptations may include: post-maturation primary seed dormancy, which prevents germination of maturing seeds before the summer; seed dispersal mechanisms with escape or protection strategies; cautious or opportunistic germination strategies; seedling drought tolerance. The beginning of the season with rain, at mild winter temperatures, is less predictable than the end of this season. Therefore, day length is an important factor in regulating flowering, the plant's life span, as well as the phenotypic plasticity of seed germination, which is also affected by maternal factors. These contribute to and increase the chance of a species surviving in its particular habitat. Such complementary sets of adaptations have developed into sets of survival strategies. They have been found to occur in some of the more common plant species that have been studied in detail over recent years. Included are complementary sets of survival strategies at different stages of the life cycles of annual plants. In some of the species tested, local genotypes that differ in their germination and primary dormancy were found to have developed. For instance, Hordeum spontaneum, Helianthemum ventosum and H. vesicarium germinate at a range of temperatures and have developed a tolerance to salt. Local genotypes with differing seedling drought tolerance occur in Schismus arabicus and Hordeum spontaneum.