The comparative population dynamics of Echium plantagineum L. between its native and invaded ranges

Echium plantagineum L. (Boraginaceae) is a winter annual rosette forb, native to the western Mediterranean Basin. In its native environment E. plantagineum is a common, but not dominant component of species-rich annual grasslands. Since its introduction into Australia during the mid-1800's E. plantagineum has spread to infest vast areas of predominantly agricultural land in south-east and south-west Australia. In this environment E. plantagineum is often abundant and can be the dominant pasture species. In an attempt to unravel the ecological factors responsible for E. plantagineum''s high population abundance in Australia, its population dynamics were compared between sites in the invaded and native ranges. Demographic parameters of E. plantagineum populations were estimated at a site near Canberra in south-eastern Australia, and at a site near Evora in southern Portugal. Identical factorial experiments were set up at each site with treatment combinations of the presence or absence of grazing, fertilisation and pasture competition. The recruitment, survival, fecundity and seed bank dynamics of E. plantagineum populations were measured within each of the treatment combinations over two seasons at each site. These data allowed the estimation of demographic transition probabilities describing the proportion of E. plantagineum individuals moving from one life cycle stage to the next for each of the site by treatment combinations. The proportion of the seed bank forming established seedlings was 2 to 5 times greater at Canberra than Evora, while the proportion of the seed rain being incorporated into the seed bank was 3 times greater at Canberra than Evora. Neither the survival rate of seeds in the seed bank, as estimated from seed burial experiments, nor the fecundity of E. plantagineum individuals differed between populations at Canberra and Evora. The survival rate of seedlings to flowering plants was always at least 2 times lower at Canberra than Evora. The demographic data were used to parameterise a density-dependent population model for E. plantagineum to simulate population trajectories for grazed and ungrazed populations at both sites. Grazed E. plantagineum populations at Canberra had modelled population abundances 5 times greater, and growth rates 3 times greater than grazed populations at Evora, results broadly consistent with field observations. A sensitivity analysis of the model showed that these greater population abundances and rates of growth at Canberra were mostly due to the greater success of seedling establishment there. A series of experiments were carried out to investigate the factors controlling E. plantagineum seedling establishment both in Mediterranean Europe and Australia. Experiments comparing the dormancy behaviour and cues required for germination showed that Australian and Mediterranean European seeds behaved similarly, other than that seeds from Evora germinated mostly in one massed event, while seeds from Canberra germinated in multiple cohorts throughout a season. A seedling removal experiment removing various classes and proportions of species during autumn germination showed that at Evora co-germinating species competed significantly with E. plantagineum seedlings and reduced their establishment success. This was not so at Canberra. These results strongly suggest that the greater rates of seedling establishment at Canberra, as compared to those at Evora, were due to differences in the intensity of competition for establishment space imposed by the different plant communities at each site. A series of glasshouse experiments, in which E. plantagineum seeds were germinated together with a range of densities of various morphological species types, identified rosette-forming species as being highly suppressive of E. plantagineum seedling establishment. The greater intensity of competition for establishment space at Evora was probably due to the considerably higher abundance of competitive rosette forb species present in the pasture there, than at Canberra. Differences in species richness between the sites may have also acted to increase the competitive effect on E. plantagineum seedlings at the richer Portuguese site through the possible supply of greater densities of competitor seedlings during autumn germination and, in interaction with climatic variation, the maintenance of competitor seedling densities between