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Université de Fribourg

Dissecting impact of plant invaders: do invaders behave differently in the new range?

Sun, Yan ; Collins, Alexandra R. ; Schaffner, Urs ; Müller-Schärer, Heinz

In: Ecology, 2013, p. -

Knowledge from basic plant ecology suggests that impact of one plant species on another is driven by either competition for the same limiting resources, or by unique plant traits. These processes might be context specific, explaining a differential impact of exotic plant invaders in the native vs. introduced range. With the help of a conceptual framework, we aimed at identifying the relationship...

Université de Fribourg

Plant interspecific differences in arbuscular mycorrhizal colonization as a result of soil carbon addition

Eschen, René ; Müller-Schärer, Heinz ; Schaffner, Urs

In: Mycorrhiza, 2012, p. -

Soil nutrient availability and colonization by arbuscular mycorrhizal fungi are important and potentially interacting factors shaping vegetation composition and succession. We investigated the effect of carbon (C) addition, aimed at reducing soil nutrient availability, on arbuscular mycorrhizal colonization. Seedlings of 27 plant species with different sets of life-history traits (functional...

Université de Fribourg

New protocols to assess the environmental impact of pests in the EPPO decision-support scheme for pest risk analysis

Kenis, Marc ; Bacher, Sven ; Baker, R. H. A. ; Branquart, E. ; Brunel, S. ; Holt, J. ; Hulme, Philip E. ; MacLeod, A. ; Pergl, Jan ; Petter, F. ; Pyšek, Petr ; Schrader, G. ; Sissons, A. ; Starfinger, U. ; Schaffner, Urs

In: EPPO Bulletin, 2012, vol. 42, no. 1, p. 21–27t

Assessing the potential environmental impact of alien plants and plant pests is notoriously difficult. New protocols have been developed in the framework of the EC project PRATIQUE to provide guidance on environmental impact assessment in the EPPO pest risk analysis (PRA) decision-support scheme and enhance consistency between risk assessors and risk ratings for different pests. A set of...

Université de Fribourg

Prospects for biological control of Ambrosia artemisiifolia in Europe: learning from the past

Gerber, E. ; Schaffner, Urs ; Gassmann, A. ; Hinz, H. L. ; Seier, M. ; Müller-Schärer, Heinz

In: Weed Research, 2011, vol. 51, no. 6, p. 559–573

The recent invasion by Ambrosia artemisiifolia (common ragweed) has, like no other plant, raised the awareness of invasive plants in Europe. The main concerns regarding this plant are that it produces a large amount of highly allergenic pollen that causes high rates of sensitisation among humans, but also A. artemisiifolia is increasingly becoming a major weed in agriculture. Recently, chemical...

Université de Fribourg

Polyploidy in phenotypic space and invasion context: a morphometric study of Centraurea stoebe s.l.

Mráz, Patrik ; Bourchier, Robert S. ; Treier, Urs A. ; Schaffner, Urs ; Müller-Schärer, Heinz

In: International Journal of Plant Sciences, 2011, vol. 172, no. 3, p. 386-402

The taxonomy of the Centaurea stoebe complex is controversial. Diploid and tetraploid plants occur in its native European range, but to date only tetraploids have been recorded from its introduced range in North America. We examined morphological differentiation of C. stoebe using multivariate and univariate approaches to clarify the taxonomic status of the known cytotypes. We measured more...

Université de Fribourg

Plant invasions, generalist herbivores, and novel defense weapons

Schaffner, Urs ; Ridenour, Wendy M. ; Wolf, Vera C. ; Bassett, Thomas ; Müller, Caroline ; Müller-Schärer, Heinz ; Sutherland, Steve ; Lortie, Christopher J. ; Callaway, Ragan M.

In: Ecology, 2011, vol. 92, no. 4, p. 829-835

One commonly accepted mechanism for biological invasions is that species, after introduction to a new region, leave behind their natural enemies and therefore increase in distribution and abundance. However, which enemies are escaped remains unclear. Escape from specialist invertebrate herbivores has been examined in detail, but despite the profound effects of generalist herbivores in natural...

Université de Fribourg

Is there rapid evolutionary response in introduced populations of tansy ragwort, Jacobaea vulgaris, when exposed to biological control ?

Rapo, Carole ; Müller-Schärer, Heinz ; Vrieling, Klaas ; Schaffner, Urs

In: Evolutionary Ecology, 2010, vol. 24, no. 5, p. 1081-1099

Differences in the herbivore community between a plant’s native (specialists and generalists) and introduced range (almost exclusively generalists) may lead to the evolution of reduced allocation to defences against specialist herbivores in the introduced range, allowing for increased allocation to competitive ability and to defences against generalist herbivores. Following this logic, the...

Université de Fribourg

Evidence for a combination of pre-adapted traits and rapid adaptive change in the invasive plant Centaurea stoebe

Henery, Martin L. ; Bowman, Gillianne ; Mráz, Patrik ; Treier, Urs A. ; Gex-Fabry, Emilie ; Schaffner, Urs ; Müller-Schärer, Heinz

In: Joural of Ecology, 2010, vol. 98, no. 4, p. 800–813

1. Introduced plants have the potential to rapidly evolve traits of ecological importance that may add to their innate potential to become invasive. During invasions, selection may favour genotypes that are already pre-adapted to conditions in the new habitat and, over time, alter the characteristics of subsequent generations. 2. Spotted knapweed (Centaurea stoebe) occurs in two predominantly...

Université de Fribourg

Aboveground environment type, soil nutrient content and arbuscular mycorrhizal fungi explain establishment success of Centaurea jacea on ex-arable land and in late-successional grasslands

Eschen, René ; Müller-Schärer, Heinz ; Schaffner, Urs

In: Plant and Soil, 2009, vol. 322, no. 1-2, p. 115-123

We studied the relative importance of the aboveground and belowground environment for survival and growth of emerged seedlings of Centaurea jacea to better understand the general difficulty of establishing late-successional species at restoration sites on ex-arable land. Potted seedlings growing on soil from six late-successional grasslands and from six ex-arable (restoration) sites were...

Université de Fribourg

Shift in cytotype frequency and niche space in the invasive plant Centaurea maculosa

Treier, Urs A. ; Broennimann, Olivier ; Normand, Signe ; Guisan, Antoine ; Schaffner, Urs ; Steinger, Thomas ; Müller-Schärer, Heinz

In: Ecology, 2009, vol. 90, no. 5, p. 1366-1377

Polyploidy is often assumed to increase the spread and thus the success of alien plant species, but few empirical studies exist. We tested this hypothesis with Centaurea maculosa Lam., a species native to Europe and introduced into North America approximately 120 years ago where it became highly invasive. We analyzed the ploidy level of more than 2000 plants from 93 native and 48 invasive C....