Comparative plant sizes and reproductive strategies in desert and mediterranean populations of ephemeral plants

Plant size at anthesis was studied in wild populations of 12 species and taxa pairs of ephemeral plants from Mediterranean and desert sites in Israel. In two of the four parameters studied, plant height and above-ground biomass, Mediterranean populations showed a significantly greater variability than the corresponding desert ones. This result is possibly correlated with the Mediterranean or steppic (Lrano-Turanian) origin of the majority of the species and taxa pairs studied. Intraspecific comparison of absolute reproductive output and of two “reproductive strategy indicators” was also carried out on three widespread grasses: two of Mediterranean origin (Brachypodium distachyon and Bromusfasciculatus) and one of desert origin (Stipa c opens is). No clear trends were recorded across taxonomic boundaries for the absolute reproductive output. However, desert populations of the three species showed a greater reproductive effort (biomass of diaspores per biomass of above-ground vegetative parts), and those of B. distachyon and S. capensis showed a higher “efficiency” of diaspore production (number of diaspores per above-ground biomass). Data are brought to indicate (a) the narrowing of variability in “outlying” or colonizing populations of the ephemerals under study, and (b) the evolution of distinct strategies of reproductive allocation in desert populations.