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Université de Fribourg

Plant neighbours rather than soil biota determine impact of an alien plant invader

Sun, Yan ; Müller-Schärer, Heinz ; Schaffner, Urs

In: Functional Ecology, 2014, vol. 28, no. 6, p. 1545–1555

1. Various factors have been shown contributing to the ecosystem impact of invasive alien plants, but their relative importance remains unclear. We focused on the effects of neighbouring plant community and soil biota as these biotic factors have been repeatedly put forward to explain invasion success (e.g. as components of the novel weapons and of the biotic release hypothesis).2. To assess...

Université de Fribourg

Contrasting spatio-temporal climatic niche dynamics during the eastern and western invasions of spotted knapweed in North America

Broennimann, Olivier ; Mráz, Patrik ; Petitpierre, Blaise ; Guisan, Antoine ; Müller-Schärer, Heinz

In: Journal of Biogeography, 2013///n/a–n/a

Aim: The spotted knapweed (Centaurea stoebe), a plant native to south-east and central Europe, is highly invasive in North America. We investigated the spatio-temporal climatic niche dynamics of the spotted knapweed in North America along two putative eastern and western invasion routes. We then considered the patterns observed in the light of historical, ecological and evolutionary...

Université de Fribourg

Effects of soil fungi, disturbance and propagule pressure on exotic plant recruitment and establishment at home and abroad

Maron, John L. ; Waller, Lauren P. ; Hahn, Min A. ; Diaconu, Alecu ; Pal, Robert W. ; Müller-Schärer, Heinz ; Klironomos, John N. ; Callaway, Ragan M.

In: Journal of Ecology, 2013, p. -

Biogeographic experiments that test how multiple interacting factors influence exotic plant abundance in their home and recipient communities are remarkably rare. We examined the effects of soil fungi, disturbance and propagule pressure on seed germination, seedling recruitment and adult plant establishment of the invasive Centaurea stoebe in its native European and non-native North American...

Université de Fribourg

Cytotype differences modulate eco-geographical differentiation in the widespread plant Centaurea stoebe

Hahn, Min A. ; Müller-Schärer, Heinz

In: Ecology, 2013, vol. 94, no. 5, p. 1005–1014

The evolution of optimal life history strategies is central for the fitness of organisms in a given environment. Besides divergent selection, other factors may determine regional patterns of differentiation and contribute to life history evolution. In a common-garden environment over three years, we examined life history differentiation across different eco-geographical regions and effects of a...

Université de Fribourg

Anthropogenic disturbance as a driver of microspatial and microhabitat segregation of cytotypes of Centaurea stoebe and cytotype interactions in secondary contact zones

Mráz, Patrik ; Španiel, Stanislav ; Keller, Andreas ; Bowmann, Gillianne ; Farkas, Alexandre ; Šingliarová, Barbora ; Rohr, Rudolf P. ; Broennimann, Olivier ; Müller-Schärer, Heinz

In: Annals of Botany, 2012, p. -

Background and Aims: In a mixed-ploidy population, strong frequency-dependent mating will lead to the elimination of the less common cytotype, unless prezygotic barriers enhance assortative mating. However, such barriers favouring cytotype coexistence have only rarely been explored. Here, an assessment is made of the mechanisms involved in formation of mixed-ploidy populations and coexistence of...

Université de Fribourg

Influence of plant phenostage and ploidy level on oviposition and feeding of two specialist herbivores of spotted knapweed, Centaurea stoebe

Collins, Alexandra R. ; Müller-Schärer, Heinz

In: Biological Control, 2011, p. -

A caged field experiment was used to determine how Centaurea stoebe L. phenostage (rosette, single-stem, multiple-stem) and ploidy level (diploid = 2× and tetraploid = 4×) influence oviposition and feeding of two biological control agents, Agapeta zoegana (Lep.: Cochylidae) and Cyphocleonus achates (Col.: Curculionidae). Ploidy level did not influence oviposition patterns of A. zoegana but...

Université de Fribourg

Polyploidy and invasion success: trait trade-offs in native and introduced cytotypes of two Asteraceae species

Thébault, Aurélie ; Gillet, François ; Müller-Schärer, Heinz ; Buttler, Alexandre

In: Plant Ecology, 2010, vol. 212, no. 2, p. 315-325

Invasion success is favoured by the introduction of pre-adapted genotypes. In addition, novel pressures in the introduced range may lead to phenotypic changes related to fitness or competitive ability of introduced plants. Polyploidy appears to be over-represented in invasive plants, but differences between cytotypes in growth strategies including trade-offs among plant traits have received...

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

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....