Temporal associations among abundances of predator, prey, and an acanthocephalan parasite in intertidal sandy shores of southern Chile
Parasite recruitment in intermediate hosts can reflect the abundance and diversity of final hosts, because the final hosts disperse the last infective stage of parasites. Therefore, in system in which the diversity of final hosts varies over time (e.g. systems including migratory birds), a concomitant variation in parasitosis on intermediate hosts should be expected. We tested this prediction along intertidal sandy shores of southern Chile, where the abundance and diversity of final hosts (four seagull species) increases during austral spring and summer. Seagull censuses, in addition to mole crab (Emerita analoga) and parasite (Profilicollis bullocki) collections were done every three months 2014 at four sandy beaches between 39°24’12’’S - 39°51’17’’S. The length of the mole crabs cephalotorax (LCT) was measured as a relevant covariable. Factorial analyses of variance with quadratic orthogonal polynomial contrasts were used to test the relationships between sampling date, and site with seagull abundance and different indicators of parasitosis, such as prevalence, abundance, and intensity of parasites. We conducted separate multiple linear regressions with seagull abundance and LCT as independent variables, and the indicators of parasitosis as dependent variables.
Preliminary results showed that abundance of seagulls and mole crabs significantly increased during summer-autumn season. Sites with more predators also had more abundance of preys. The interaction between season and site was statistically non-significant, indicating that the differences among seasons were consistent across sites and vice versa. Despite these significant patterns, the indicators of parasitosis remained statistically similar among seasons and sites. Multiple linear regressions showed that LCT was the best predictor of parasite abundance, but not of prevalence and intensity. Therefore, our results suggest that the spatiotemporal variation in predator abundance, but not necessarily in parasites, is related to that in prey abundances. The response of parasitosis to factors such as productivity, prey size structure, random infection, and host switch should be elucidated.