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Wolf V.C.,Bielefeld University | Berger U.,Bielefeld University | Gassmann A.,CABI Europe Switzerland | Muller C.,Bielefeld University
Biological Invasions | Year: 2011

Mechanisms contributing to the invasive success of plants are still only partly understood. A main assumption is that an escape from specialized enemies in introduced ranges allows a reduction of chemical defences resulting in an increase in growth and reproduction and thus increased competitive ability of introduced plants. Not only variation in concentration but also variation in composition of chemical compounds between individuals may be a key advantage for plants introduced to novel areas impeding adaptation of different plant antagonists. To investigate quantitative and qualitative variation of putative defence compounds and investment of resources in growth, we conducted a common garden experiment in the native range with seeds of 13 native and 9 introduced populations of Tanacetum vulgare, an aromatic plant forming different chemotypes. After 3.5 months, plants of introduced populations had similar biomass but more stems and higsher concentrations of volatile secondary compounds (mainly terpenes) than plants of native populations. Both native and invasive T. vulgare populations exhibited high chemotypic variation with nine chemotypes occurring on both continents, whereas several were found exclusively either in plants originating from the native (n=10) or invasive (n=2) range. Due to the known negative effects of many mono- and sesquiterpenes on various organisms, we propose that high concentrations of these secondary compounds accompanied by high chemotypic diversity may facilitate the invasion success of a plant species. © 2011 Springer Science+Business Media B.V. Source


Partial life histories for eight Afro-tropical Coeliadinae are described and illustrated: Pyrrhochalcia iphis (Drury) (Côte d'Ivoire), Pyrrhiades lucagus (Cramer) (Ghana), P. anchises anchises (Gerstaecker) (Kenya), Coeliades chalybe chalybe (Westwood) (Côte d'Ivoire), C. forestan forestan (Stoll) (Kenya), C. pisistratus (Fabricius) (Kenya), C. sejuncta (Mabille & Vuillot) (Kenya), C. kenya Evans stat. rev. (Kenya). Descriptions of a further six species or subspecies are provided from the literature: P. anchises jucunda (Butler) (Oman), P. aeschylus (Plötz) (Republic of Guinea), P. pansa (Hewitson) (Réunion), C. bixana Evans (Democratic Republic of the Congo), C. libeon (Druce) (Democratic Republic of the Congo), C. keithloa (Wallengren) (South Africa), C. lorenzo Evans stat. rev. (South Africa). Unpublished photographs provided by T.C.E. Congdon illustrate early stages of C. sp. probably fervida (Butler) and C. rama Evans (Madagascar). Notes based on museum material are presented for C. ramanatek (Boisduval). Generalisations are made for the subfamily in Africa and the implications for generic groupings in the subfamily are considered. All except C. libeon are known to feed on at least one species of Malpighiaceae, while C. libeon feeds on at species of at least two other families of Malpigiales. A new type of leaf shelter, the four-cut shelter, is introduced, characteristic of African Coeliadinae. Source


Henery M.L.,University of Fribourg | Bowman G.,University of Fribourg | Mraz P.,University of Fribourg | Treier U.A.,University of Aarhus | And 3 more authors.
Journal of Ecology | Year: 2010

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 spatially separated cytotypes in its native range (Europe-Western Asia), but currently only the tetraploid form has been confirmed in the introduced range (North America), where it is invasive. We used several common garden experiments to examine, across multiple populations, whether tetraploids and diploids from the native range differ in life cycle, leaf traits and reproductive capacity and if such differences would explain the predominance of tetraploids and their advance into new habitats in the introduced range. We also compared the same traits in tetraploids from the native and introduced range to determine whether any rapid adaptive changes had occurred since introduction that may have enhanced invasive potential of the species in North America.3. We found tetraploids had lower specific leaf area, less lamina dissection and fewer, narrower leaves than diploids. Diploids exhibited a monocarpic life cycle and produced few if any accessory rosettes. Diploids produced significantly more seeds per capitulum and had more capitula per plant than tetraploids. In contrast, the vast majority of European tetraploids continued to flower in both seasons by regenerating from multiple secondary rosettes, demonstrating a predominantly polycarpic life cycle.4. During early growth tetraploids from North America achieved greater biomass than both tetraploids and diploids from the native range but this did not manifest as larger above-ground biomass at maturity. In North American tetraploids there was also evidence of a shift towards a more strictly polycarpic life cycle, less leaf dissection, greater carbon investment per leaf, and greater seed production per capitulum.5.Synthesis. Our results suggest that the characteristics of tetraploid C. stoebe pre-adapted them (compared to diploid conspecifics) for spread and persistence of the species into habitats in North America characterized by a more continental climate. After the species' introduction, small but potentially important shifts in tetraploid biology have occurred that may have contributed significantly to successful invasion. © 2010 The Authors. Journal compilation © 2010 British Ecological Society. Source


de Clercq P.,Ghent University | Mason P.G.,Agriculture and Agri Food Canada | Babendreier D.,CABI Europe Switzerland
BioControl | Year: 2011

The use of exotic (=alien) arthropods in classical and augmentative biological control programs has yielded huge economic and ecological benefits. Exotic species of arthropods have contributed to the suppression of key pests in agriculture and forestry or have aided in restoring natural systems affected by adventive species. However, adverse non-target effects of exotic biological control agents have been observed in a number of projects. Non-target effects range from very small effects, e. g. 2% parasitization on a non-target insect on a local level, to massive effects on a large scale. Until now, no consensus on how to judge the magnitude of non-target effects and whether these effects can be tolerated or are unacceptable has emerged. In this paper, we briefly review both the benefits of biological control as well as the associated risks including to human and animal health, plant health and particularly the environment. We also make an attempt at identifying the major challenges for assessing risks and for balancing benefits and risks. There is general agreement that sound risk assessment procedures should precede the release of exotic invertebrate biological control agents and a recent shift-especially for arthropod biological control-from introductions done without meaningful risk assessment studies to projects conducting thorough host range testing can be observed. However, overly stringent regulations that would preclude promising agents from being developed must be avoided. © 2011 International Organization for Biological Control (IOBC). Source


Parepa M.,University of Bern | Parepa M.,University of Tubingen | Fischer M.,University of Bern | Krebs C.,CABI Europe Switzerland | And 2 more authors.
Evolutionary Applications | Year: 2014

Hybridization is one of the fundamental mechanisms by which rapid evolution can occur in exotic species. If hybrids show increased vigour, this could significantly contribute to invasion success. Here, we compared the success of the two invasive knotweeds, Fallopia japonica and F. sachalinensis, and their hybrid, F. × bohemica, in competing against experimental communities of native plants. Using plant material from multiple clones of each taxon collected across a latitudinal gradient in Central Europe, we found that knotweed hybrids performed significantly better in competition with a native community and that they more strongly reduced the growth of the native plants. One of the parental species, F. sachalinensis, regenerated significantly less well from rhizomes, and this difference disappeared if activated carbon was added to the substrate, which suggests allelopathic inhibition of F. sachalinensis regeneration by native plants. We found substantial within-taxon variation in competitive success in all knotweed taxa, but variation was generally greatest in the hybrid. Interestingly, there was also significant variation within the genetically uniform F. japonica, possibly reflecting epigenetic differences. Our study shows that invasive knotweed hybrids are indeed more competitive than their parents and that hybridization increased the invasiveness of the exotic knotweed complex. © 2013 The Authors. Source

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