The comparative demography of the pasture weed Echium plantagineum between its native and invaded ranges

Abstract

Summary 1.Echium plantagineum is native to the western Mediterranean Basin, where it is a common, but not dominant, component of species-rich annual grasslands. Since its introduction into Australia, E. plantagineum has spread to infest vast areas of predominantly agricultural land in south-east and south-west Australia, where it can be the dominant pasture species. 2. To unravel the ecological factors responsible for the high population abundance of E. plantagineum in Australia, its demography was 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 and pasture competition. 3. The recruitment, survival, fecundity and seed bank dynamics of E. plantagineum populations were measured for each of the treatment combinations over 2 years at each site. These data allowed the estimation of demographic parameters describing the proportion of E. plantagineum individuals moving from one life-cycle stage to the next. 4. Seedling establishment fractions were two to five times greater at Canberra than at Evora, and seed bank incorporation rates were three times greater at Canberra than Evora. These demographic differences were those most likely to play an important role in the greater abundance of E. plantagineum in Australia compared with Mediterranean Europe. Neither seed bank survival rates nor seed production differed between populations at Canberra and Evora, while seedling survival rates were always lower at Canberra than at Evora. 5. Neither grazing nor pasture competition limited the seed production or seedling survival of E. plantagineum populations at Evora more than at Canberra. 6. An effective approach for the control of E. plantagineum in Australia may thus be through the reduction of the seedling establishment fraction. This may be achieved by maintaining significant pasture vegetation cover and reducing the available space for E. plantagineum establishment during autumn.

Introduced populations of Genista monspessulana (French broom) are more dense and produce a greater seed rain in California, USA, than native populations in the Mediterranean Basin of Europe

“…Populations in the introduced region also showed a broader age structure than populations in the native region with a greater percentage of seedlings and thus a slightly lower mean plant age. Lloyd (2000) found similar seedling recruitment patterns when comparing the density of G. monspessulana field populations between Europe and Australia, and higher seedling recruitment has been attributed to the success of a range of other invasive plant species (Grigulis et al 2001;Erfmeier and Bruelheide 2004). Although these results show improved performance of G. monspessulana field populations in California compared to those in the Mediterranean basin, such data do not distinguish between phenotypic plasticity and adaptive evolution as mechanisms for its success in California.…”

“…Reduced post-dispersal seed predation may also contribute to the larger seed bank density of G. monspessulana in the introduced region. For example, predation rates by rodents were significantly higher on seed banks in native than introduced regions for C. scoparius , and reduced seed harvesting by ants was considered a key factor explaining the success of Echium plantagineum in its introduced region (Grigulis et al 2001). While anecdotal evidence indicates that G. monspessulana seeds are dispersed/ predated by ants, birds, and other animals in the USA, this has not been quantified (Bossard 2000) and may well be less than in the native region as for C. scoparius.…”

“…Quantitative data comparing plant parameters of native and introduced field populations has grown steadily over the last 10 years, and published studies have demonstrated that introduced plant species often do show greater population size or density (Vilà et al 2005), plant size (Jakobs et al 2004) and growth rate (Erfmeier and Bruelheide 2004), seed size (Buckley et al 2003), reproductive output (Stastny et al 2005), seed bank (Lloyd 2000), and seedling recruitment rate (Grigulis et al 2001). These patterns are not always consistent, as individual plant species do not always express differences in all the plant-growth parameters measured between native and introduced populations (Vilà et al 2005;van Kleunen and Fischer 2008;Beckmann et al 2009).…”

Do invasive species perform better in their new ranges?

“…In support, individuals in introduced populations can indeed be larger (Crawley 1987, Grosholz and Ruiz 2003, Jakobs et al 2004), more fecund (Grigulis et al 2001, Stastny et al 2005, and more abundant (Freeland 1990, Hinz and Schwarzlaender 2004, Prati and Bossdorf 2004, Hierro et al 2005, Vila et al 2005, Herrera et al 2011). These differences have been linked to novel conditions as a way of explaining invasion success (e.g., Torchin et al 2001, Mitchell and Power 2003, Alba and Hufbauer 2012.…”

Demography of the Invasive Geophyte Oxalis pes-caprae Across a Mediterranean Island

“…The spatial variability of invader reproductive components is evident both among and within the communities (i.e. microhabitat) (Vilà and D'Antonio, 1998b;Grigulis et al, 2001;Lambrinos, 2002) suggesting that a realistic view of an invader's performance should encompass multiple sites within the area of introduction.…”