Fig. 1

Graph derived from three examples of endoparasite overdispersion [23, 24]. Example A, a more marginal example of aggregation shows data for tapeworm infection (Triaenophorus nodulosus) in perch (Perca fluviatilis). In this example 54% of the tapeworms were in 18.5% of hosts with 81.5% uninfected or lightly infected. Example B shows pronounced overdispersion of the nematode (Porrocaecum ensicaudatum) in starlings (Sturnus vulgaris). In this case, 89% of the hosts are uninfected or lightly infected, and 69% of the parasites were recorded in 11% of the hosts. Example C shows a very pronounced case of overdispersion for nematodes (Spiroxys japonica) in pond frogs (Rana nigromaculata). In this case, 70% of the parasites were recorded in just 4% of the hosts while 88% of the hosts were uninfected and 8% had light infections.