Food webs and the predators within them are changing with the influx of introduced species. Increasing introductions have led to the accumulation of multiple introduced predators in many locations. The study of interactions among introduced species is very much in its infancy and in Chapter 1, I used meta-analysis to frame what is currently known about these types of interactions. I compared the magnitude of facilitative and antagonistic ISI on the performance of introduced species in their non-native ranges, and found that overall, antagonism and facilitation appear to be equivalent in their determination of introduced species success. Within particular ecological contexts, however, antagonism or facilitation can dominate among introduced species, producing patterns of rapidly increasing introduced species accumulation as in invasional meltdown, or producing “Surprise effects” such as those first described on heavily invaded islands where management efforts were stymied due to cryptic interactions among introduced species. Methods vary regarding detection of interactions among introduced species and the impacts of those interactions, and very few if any generalizations have yet been made regarding the role of introduced species interactions in altering the structure of native communities.
In chapter 2 I describe laboratory and field manipulations designed to determine whether the introduced cephalaspidaean Philine orientalis interferes with the invasive predatory crab Carcinus maenas . Laboratory and field investigations produced conflicting results. In the laboratory, P. orientalis slowed predation of C. maenas on the introduced gem clam Gemma gemma, likely due to the secretion of distasteful, defensive mucous by P. orientalis. In the field, this suppression did not occur. I used laboratory and field observations to parameterize a foraging model for C. maenas in the presence of P. orientalis based on the Beddington-DeAngelis functional response equation. This model revealed that crab foraging efficiency was likely to be the most important determining factor in whether or not suppression by P. orientalis alters the predatory impact of C. maenas on small clams like G. gemma. Foraging efficiency is predicted to decrease with increasing predator density.
In chapter 3, I investigated the potential for an emergent multiple predator effect between C. maenas and the native predatory crab Cancer productus. It was not clear whether an emergent effect exists between these two speices, but results indicated that risk reduction is a likely outcome of these predators being combined in the field. Any negative effect of C. maenas on C. productus foraging, or vice versa, was a result of increased predator density, a common consequence of successful introduction of non-native predators. The decrease of predator foraging efficiency at high predator densities could produce a situation in which additional interference from other organisms, such as that discussed in chapter 2, would become ecologically important.
Through meta-analysis and experimentation, this dissertation outlines how interaction webs and communities change with the influx of introduced predators via predator-predator interference. I suggest that these changes can be highly context-specific, and therefore a multi-faceted approach is required to understand their true impact throughout a food web. In this case, a potential route of interference was identified between P. orientalis and C. maenas that is likely to be mediated by a chemical defense of P. orientalis, a supposedly rare occurance in soft-bottom communities. The ecological importance of this interference is predicted to change as crab foraging efficiency changes. These kinds of contextual details are a determining factor of the magnitude of the impact of new predator introductions on native communities.
|Advisor:||Williams, Susan L.|
|Commitee:||Grosholz, Edwin, Sih, Andrew|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 73/07(E), Dissertation Abstracts International|
|Keywords:||Interactions, Introduced species, Marine predators, Native epifaunal predators, Predation|
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