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- Enge, Swantje, 1981, et al.
(författare)
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An exotic chemical weapon explains low herbivore damage in an invasive alga
- 2012
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Ingår i: Ecology. - : Wiley. - 0012-9658. ; 93:12, s. 2736-2745
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Tidskriftsartikel (refereegranskat)abstract
- Invasion success of introduced species is often attributed to a lack of natural enemies as stated by the enemy release hypothesis (ERH). The ERH intuitively makes sense for specialized enemies, but it is less evident why invaders in their new area escape attacks by generalist enemies. A recent hypothesis explains low herbivore damage on invasive plants with plant defense chemicals that are evolutionarily novel to native herbivores. Support for this novel weapon hypothesis (NWH) is so far based on circumstantial evidence. To corroborate the NWH, there is a need for direct evidence through explicit characterizations of the novel chemicals and their effects on native consumers. This study evaluated the NWH using the highly invasive red alga Bonnemaisonia hamifera. In pairwise feeding experiments, preferences between B. hamifera and native competitors were assessed for four common generalist herbivores in the invaded area. Through a bioassay-guided fractionation, we identified the deterrent compound and verified its effect in an experiment with the synthesized compound at natural concentrations. The results showed that native herbivores strongly preferred native algae to B. hamifera. The resistance against herbivores could be tracked down to the algal metabolite 1,1,3,3-tetrabromo-2-heptanone, a compound not known from native algae in the invaded area. The importance of the chemical defense was further underlined by the feeding preference of herbivores for individuals with a depleted content of 1,1,3,3-tetrabromo-2-heptanone. This study thus provides the first conclusive example of a highly successful invader where low consumption in the new range can be directly attributed to a specific chemical defense against evolutionarily naive native generalists. In conclusion, our results support the notion that novel chemical weapons against naive herbivores can provide a mechanistic explanation for plant invasion success.
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| 4. |
- Svensson, J. Robin, 1979, et al.
(författare)
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Physical and biological disturbance interacts differently with productivity: divergence in effects on floral and faunal richness
- 2010
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Ingår i: Ecology. - 0012-9658. ; 91:10, s. 3069-3080
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Tidskriftsartikel (refereegranskat)abstract
- Physical and biological disturbance are ecological processes affecting patterns in biodiversity at a range of scales in a variety of terrestrial and aquatic systems. Theoretical and empirical evidence suggest that effects of disturbance on diversity differ qualitatively and quantitatively depending on levels of productivity (e.g. the dynamic equilibrium model). In this study we contrasted the interactive effects between physical disturbance and productivity to those between biological disturbance and productivity. Furthermore, to evaluate how these effects varied among different components of marine hard-substratum assemblages, analyses were done separately on algal and invertebrate richness, as well as richness of the whole assemblage. Physical disturbance (wave action) was simulated at five distinct frequencies, while biological disturbance (grazing periwinkles) was manipulated as present or absent, and productivity as high or ambient. Uni- and multivariate analyses both showed significant effects of physical disturbance and interactive effects between biological disturbance and productivity on the composition of assemblages and the total species richness. The algal richness was significantly affected by productivity and biological disturbance, whereas the invertebrate richness was affected by physical disturbance only. Thus, we show, for the first time, that biological disturbance and physical disturbance interact differently with productivity, because these two types of disturbance affect different components of assemblages. These patterns might be explained by differences in the distribution (i.e. press vs. pulse) and degree of selectivity between disturbances. Because different types of disturbance can affect different components of assemblages, general ecological models will benefit from using natural diverse communities and studies concerned with particular subsets of assemblages may be misleading. In conclusion, this study shows that the outcome of experiments on effects of disturbance and productivity on diversity is greatly influenced by the composition of the assemblage under study, as well as on the type of disturbance that is used as an experimental treatment.
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| 5. |
- Toth, Gunilla B., 1973, et al.
(författare)
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Inducible and constitutive defenses of valuable seaweed tissues: Consequences for herbivore fitness
- 2005
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Ingår i: Ecology. - : Wiley. - 0012-9658. ; 86:3, s. 612-618
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Tidskriftsartikel (refereegranskat)abstract
- Optimal Defense Theory predicts that plants exposed to herbivory should allocate more resources to produce costly secondary metabolites in tissues with higher fitness values. To increase plant resistance, the secondary metabolites must have a negative impact on the preference and/or performance of herbivores. We tested the hypotheses that induction of secondary metabolites (phlorotannins) in a brown seaweed in response to grazing by herbivorous gastropods will differ between seaweed tissues with different fitness values (basal stipes and annual shoots), and that the subsequent change in food value will affect the fitness (growth and fecundity) of the gastropods. Induction of phlorotannins was significant in both tissue types but was more pronounced in basal stipes, which have a higher fitness value. Basal tissues also had significantly higher constitutive defense levels than did apical tissues. No effects of algal tissue type or grazing history on the growth rate of the gastropods were detected. However, the number of viable eggs was significantly lower for gastropods feeding on basal shoots, and there was a significantly lower proportion of viable eggs produced by gastropods that were offered previously grazed seaweed tissues. The results show that induced resistance, and its variation among different plant parts, call have significant negative effects on herbivore performance that may reduce future herbivore pressure and thus enhance plant fitness.
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