5 research outputs found
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Mechanisms of invasion resistance: competition among intertidal mussels promotes establishment of invasive species and displacement of native species
Understanding interactions between invasive species and recipient communities is essential to determining whether invasive species will become established and spread. In this study, we explored the role of competition and the specific mechanisms of interaction in limiting the spread of the Mediterranean bay mussel Mytilus galloprovincialis within a Pacific Northwest invasion front. We examined the role of direct (interference) and indirect (exploitation) mechanisms of competition among M. galloprovincialis and 2 native mussels (M. trossulus and M. californianus). As the fastestgrowing organisms are often competitively dominant in space-limited systems, such as rocky intertidal communities, we used changes in relative performance (growth and survival) in monocultures and polycultures to assess interactions among mussels. Performance of M. galloprovincialis was always greater than that of the 2 native species of mussels in both field and laboratory manipulations of species composition and density, indicating that interspecific competition did not strongly limit the growth or survival of the invader. Moreover, the presence of M. galloprovincialis consistently led to both reduced growth and survival of M. trossulus. Laboratory studies of mussel feeding and behavior revealed M. galloprovincialis to be a robust interference competitor. The invader restricted movement, smothered and interfered with filter feeding of the 2 native species of mussels. Rather than limiting invasion, interference competition gave M. galloprovincialis a competitive advantage over the native mussels. Our results suggest M. galloprovincialis may have contributed to the displacement of M. trossulus along much of its historic southern range. ©Inter-Research 2009
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Invasion resistance on rocky shores: Direct and indirect effects of three native predators on an exotic and a native prey species
Trophic relationships among native and exotic species produce novel direct and indirect interactions that can have wide-ranging community level effects and perhaps confer invasion resistance. We investigated whether native predators have the potential to directly limit the spread of the exotic mussel Mytilus galloprovincialis or mediate interactions among native and invasive mussels at a rocky intertidal invasion front in northern California. Lower survival of M. galloprovincialis in transplanted cultures exposed to predators indicated that the invader was more vulnerable to predators than the numerically dominant native M. californianus. Survival and per capita mortality rate in monocultures and polycultures did not vary for either M. galloprovincialis or M. californianus, suggesting that predator-mediated apparent competition and associational defense did not occur. Complementary laboratory feeding trials determined which among 3 intertidal predators preferred the exotic to 2 native species of mussel. The whelk Nucella ostrina was most selective, consuming the thinner shelled mussels (M. galloprovincialis and the native M. trossulus) rather than the thickershelled native species M. californianus. The crab Cancer antennaiius and the sea star Pisaster ochraceus showed no preferences among mussel species. N. ostrina were commonly observed among field-transplanted mussels; thus whelk prédation may be especially important in limiting the establishment of the invasive mussel. However, 15% of M. galloprovincialis remained intact in the field after 1 yr, suggesting that prédation alone may not inhibit establishment of the invader. A tenuous balance between larval settlement and early post-settlement prédation likely characterizes the invasion front. © Inter-Research 2009
Forecasting invasions: resource use by mussels informs invasion patterns along the South African coast
Can the enemy release hypothesis explain the success of invasive alien predators and parasitoids?
Biological invasions are ecologically and economically costly. Understanding the major
mechanisms that contribute to an alien species becoming invasive is seen as essential for limiting the
effects of invasive alien species. However, there are a number of fundamental questions that need
addressing such as why some communities are more vulnerable to invasion than others and, indeed,
why some alien species become widespread and abundant. The enemy release hypothesis (ERH) is
widely evoked to explain the establishment and proliferation of an alien species. ERH predicts that an
alien species introduced to a new region should experience a decrease in regulation by natural enemies
which will lead to an increase in the distribution and abundance of the alien species. At the centre of
this theory is the assumption that natural enemies are important regulators of populations.
Additionally, the theory implies that such natural enemies have a stronger regulatory effect on native
species than they do on alien species in the introduced range, and this disparity in enemy regulation
results in increased population growth of the alien species. However, empirical evidence for the role of
the ERH in invasion success is lacking, particularly for invertebrates. Many studies equate a reduction
in the number of natural enemies associated with an alien species to release without studying
population effects. Further insight is required in relation to the effects of specific natural enemies on
alien and native species (particularly their ability to regulate populations). We review the role of
ecological models in exploring ERH. We suggest that recent developments in molecular technologies
offer considerable promise for investigating ERH in a community context