Community ecology of parasitesfunctional and network approaches

Resumen

We should focus on features meaningful at the community level, as the diversity of the community, to ascertain the rules that manage the community composition. The term diversity includes taxonomic, phylogenetic or functional information about the evolutionary and ecological histories of the organisms, and it can be partitioned across hierarchical levels. The simultaneous measurement of the three facets of diversity at different levels is relevant to understand the composition of the diversity in a community. Other definitions of diversity propose to include the strength of interactions among organisms in the measurement of diversity, since the patterns of interactions among organisms can also produce measurable variability between communities. The study of parasite communities has always lagged behind general community ecology, despite parasites being ubiquitous in all ecosystems and parasites play key roles in ecological processes. I attribute this fact to two main causes. First, the parasitic lifestyle complicates the quantification of the effects of these organisms on the community. Second, parasitologists have commonly adopted a descriptive approach, despite the unrivaled benefits of moving forward a predictive science. This doctoral thesis aims to increase our knowledge of the community ecology of parasites, with special attention to the helminth parasite communities of grey mullets (Teleostei: Mugilidae). I will focus on the study of parasite diversity and host–parasite dynamics by means of Rao’s index of diversity and the bipartite network analysis. I have reached the following conclusions. First, the two methods developed in Chapter 3 to estimate mass of small organisms were accurate and did not significantly differ from the direct methods, whereas the traditional Geometric Approximation approach overestimated mass. Consequently, I strongly recommend abandoning its use. Second, I expect that the theoretical framework of functional traits presented in Chapter 4 will help future researchers to unveil ecological and evolutionary questions in parasitology. Moreover, I hope it will facilitate ecologists to include parasites in their studies. Third, taking advantage of the methods (Chapter 3) and theoretical considerations (Chapter 4) I found in Chapter 5 that the diversity of the parasite communities from grey mullets from the Mediterranean is dependent on the level of the analysis and the facet of diversity considered. So, parasite communities cannot be fully understood if any of the facets of diversity is neglected in a study. Fourth, I conclude in Chapter 6 that grey mullet individuals of two species play different roles for their parasite communities regarding the native or invasive status of the host individuals and the characteristics of the parasite community considered. Thus, the long-term monitoring of the roles of invasive hosts in parasite communities can be used to estimate the maturity of the establishment of an invasive hosts species.