Fig. 4.

Schematic representation of how parasite specificity and host vulnerability may contribute to the structure of fish-parasite networks according to Strona et al. (2013). Specialist parasites tend to use hosts that are easy to encounter, i.e. hosts (i) persisting over long evolutionary time, (ii) broadly distributed, and/or (iii) locally abundant. These properties are inversely related with host vulnerability to extinction. The presence of a gradient in parasite host specificity could promote the emergence of a nested structure.