Seed Dispersal and Seed Predation of Plant Species in the Negev Desert

Abstract

The importance of dispersal mechanisms is that they bring at least some seeds to the most propitious place for germination and seedling development. The great majority of annual plants inhabiting the Negev desert have very small seeds which mature and disperse at the beginning of the summer (Figs. 52, 53). Annuals with small seeds complete their life cycles in a very short time (Fig. 135; table 65). Some plants produce very large numbers of seeds per 1 m². In 1972/73, a season with only 48 mm of rain, 13 plants per 1 m² of Schismus arabicus, which grows to a few cm in height (Fig. 54), produced 1800 seeds (grains). One year later, in 1973/74, after 155 mm of rain (about 100 mm is the average rainfall) 89 plants per 1 m² produced 10,000 seeds (0.5 × 0.7 mm; weight: 0.07 mg) in the same location (Table 63). Spergularia diandra (Fig. 55) plants produce even lighter seeds (0.018 mg). In 1973/74, 36 plants per 1 m² produced 32,000 seeds. Filago desertorum (Fig. 56), in the centre of a depression, produced as many as 36,000 seeds (achenes), and Carrichtera annua (Figs. 57, 58), produced 5,200 much larger seeds per 1 m² (Figs. 131, 132) (Loria and Noy-Meir 1979/80). Such large numbers of small seeds, as well as their long viability, are a result of the selective pressure of seed predation under unpredictable amounts of rain, and the short growing season (Sects. 6.1.2, 6.1.3).