Ontogenetic changes in heterogeneity of parasite communities of fish: disentangling the relative role of compositional vs abundance variability

TIMI, JUAN T.; LANFRANCHI, ANA L.

Viña del Mar

Simposio; VII International Symposium of Fish Parasites; 2011

Fish size is a key determinant of parasite community structure. Increasing numbers of both species and individuals in longer fish is a common pattern, due to larger bodied hosts can accommodate more parasites and ingest larger quantities of food, increasing exposure to infective stages. Fish size is generally correlated to age and trophic level, therefore, larger host accumulate long lived parasites over time and broaden the spectrum of potential parasites by feeding on larger preys, acquiring qualitative- or quantitatively different assemblages as they grow. It has been shown that juvenile fish or those with low trophic level harbour more variable assemblages than their counterparts. However, an important issue remains unsolved: how much of this variability is driven by differences in composition or abundance of assemblages? We address this issue using multivariate dispersions in infracommunities of Conger orbignianus as measures of β-diversity, using a set of dissimilarity measures with different degrees of emphasis on composition vs. relative abundance information. The average distance from infracommunities to their size class centroid in the multivariate space varied along an ontogenetic gradient, its significance depended on the measure used. Larger fish showed higher richness and abundance. However, smaller fish displayed lower variations in abundance but higher in composition. This could be drawn by stochastic events of encounter at low densities due to the dilute nature of parasites in previous hosts. As fish grow, assemblage´s composition becomes homogenized by repeated exposure, with abundance thus rising as the main source of variability. Discerning between both variables is crucial to understand how community structure is drawn by size-dependent variability of host populations.