Modelling the impact of multi-­host helminth parasites on hosts’ population dynamics

This work is inspired by multi-annual observations of helminth infection levels and population densities of rock partridge (Alectoris graeca saxatilis) that is an endangered species in the Dolomitic Alps (northern Italy). Field data show that the nematode parasite Ascaridia compar infect both rock partridge and black grouse (Tetrao tetrix), and also suggest a competitive interaction between the two galliform species that share a common spatial domain in the Alps. We hypothesized two possible interaction mechanisms: direct competition and parasite-mediated competition, also called apparent competition, and we used mathematical models as a proof-­-of-­-principle verification of these hypotheses. Outputs from the direct competition model are in contrast with field observations, outputs of the parasite-­mediated competition model qualitatively fit the observed pattern suggesting that the sharing of parasite free-living stages between the two species can trigger the competition playing an important role in the decline of rock partridge in Trentino region. The model has been extended to a spatial model that allows for a partial habitat overlap, showing the role of diffusion in shaping either exclusion or spatial segregation of the competitor less tolerant of infestation