THE COMPARATIVE BIOLOGY OF PARASITE SPECIES-DIVERSITY - INTERNAL HELMINTHS OF FRESH-WATER FISH

(1) This paper describes and analyses the mean number of parasitic helminth species per host individual among Canadian freshwater fish. (2) Helminth diversity varies among host species. (3) The diversities of different taxa of helminths are correlated both within and among host species. (4) Helminth diversity is positively correlated with host size, longevity, diet and geographical range. Size (or longevity) produces the strongest correlations; when the effect of size is removed, only diet remains correlated with helminth diversity. Size and diet together explain about 40% of variance in helminth diversity among host species; the model is most successful for cestodes, where about 60% of the variance is explained. (5) Most of the ecological covariance of helminth diversity is displayed at rather high taxonomic levels, perhaps because of lag between host evolution and parasite adaptation.