| Summary: | 博士 === 國立臺灣師範大學 === 生命科學研究所 === 99 === Parasites are ubiquitous in ecological communities but they haven’t been routinely included in food web studies until very recent. Using recently published data and the tool of network analysis, I elucidated features associated with the pattern of parasitism in food web networks. First, I showed that parasites are not only occurring in non-random fashion in food webs but also positively associated with the prominent network positions occupied by their hosts. Meanwhile, a host species with high parasite diversity tends to have a wide diet range, occupy a network position close to many prey species, or occupy a network position that can better accumulate resources from species at lower trophic levels, whereas a host species with higher vulnerability to predators, being at a network position close to many predatory species, or being involved in many different food chains, tends to serve as a good intermediate host in parasite transmission. Second, by conducting simulation experiments with different food web models and extinction scenarios, I demonstrated that the reduction in food web robustness after considering parasites is mainly contributed by the life cycle constrain of parasites. The finding further demonstrates that parasites are prone to secondary extinctions and their extinctions occur earlier than those involving non-parasite species. The evident vulnerability nature of parasite to species loss designates parasite a proper leading indicators of food web integrity. Lastly, with the extension of a previously developed methodology, a new approach is presented and used to quantify the interaction structure of a food web and consequently the topological importance of species when the food web is viewed as a signed digraph. This method is also capable to quantify the strength of inter-specific interaction as well as in what way species interact with each other after counting both direct and indirect cascades in both top-down and bottom-up directions. As it has the potential to quantify a wide range of ecological interactions, its further application on revealing the interaction structures between parasites and other functional groups in food web with parasites is evidently achievable.
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