Demography and role of the seed bank in Mediterranean and desert populations of wild barley

We compared the demography of two populations of wild barley, Hordeum spontaneum, that occupy environments of different aridity (desert and Mediterranean) and represent distinct parts of the species' distribution (periphery and core) in Israel. Our demographic study included a survey of survival and fecundity of adults in quadrate plots marked at two sites in natural vegetation (one site per population), and the creation of experimental seed banks examined over three years. We measured variability in population growth rate and investigated the role of the seed bank in the demography of two populations. The latter employed construction of two-stage, three age-class transition matrices and usage of elasticity analysis. At both sites, population dynamics appear to be transient with high fluctuations of population growth rate due to variability in annual rainfall and, most likely, intra- and inter-specific density dependence. The importance of the seed bank differed among two populations. Seed dormancy had almost no demographic effect on the Mediterranean population, while it was of paramount importance in the desert population. The two populations also differed in seed and seedling survival and per adult fecundity, presumably due to the difference between two sites in (i) relative impact of seed predation, (ii) effects of density dependence on population demography, and (iii) lower vigor of seeds of desert vs. Mediterranean origin. Our study highlights the importance of life history adaptations that may evolve under specific selective forces in different parts of a species' range, which, in certain circumstances, may be critical for the persistence of a species.