Assembly rules of helminth parasite communities in grey mullets: combining components of diversity

Overview & Synopsis

Organisms associate themselves in ecological communities. It has been widely debated whether these associations are explained by deterministic or, in contrast, random processes. The answer may vary depending on the level of an organisational scale (α, β and γ) and the facet of diversity considered: Taxonomic (TD), Functional (FD) and Phylogenetic (PD). Diversity at the sampling unit (i.e. host individual) is the α diversity; β diversity represents the extent of dissimilarity in diversity among sampling units (within a level of an organisational scale, β1; between levels of an organisational scale, β2); and the total diversity of a system is γ diversity. Thus, the combination of facets and levels of scale may be useful to disentangle the mechanisms driving the composition of a parasite community. Using helminth parasite TD, FD, and a Proxy of PD (PPD) of three species of grey mullets (Teleostei: Mugilidae) from the Mediterranean Sea, we show that random and deterministic processes of different nature explain the assemblage of parasite communities. The parasite community at a host individual (α) was invariably a random subset of the total diversity in the community for the three facets of diversity. At β1 level, TD was lower than expected by chance, whereas FD and PPD were random. At β2, diversity patterns suggested environmental filtering of the parasite assemblage: species, trait, and phylogenetic compositions of parasite communities seem to depend primarily on the species of host, but also on the locality and season. Our study shows that parasite communities are not totally understood if any of the components (i.e. facets and levels) of diversity is neglected.