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sur le développement des zones arides et semi-arides

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

Auteur : Grigulis, Karlis Alfred

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 1999

Résumé partiel
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.

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