Host specificity and exchange of intestinal helminths among four species of grebes (Podicipedidae)

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Abstract
The infracommunities of intestinal helminths in 96 birds belonging to four species of grebes taken from lakes in Alberta were examined for patterns of species co-occurrence and relative abundance. Infracommunities were large (averages of 360–3640 worms) and complex (averages of 6.4–10.7 species). Three species of grebes (Aechmophorus occidentalis, Podiceps grisegena, P. nigricollis) had distinctive infracommunities, each characterized by a set (5–10) of frequent and numerous core helminth species, which regularly co-occurred with a consistent rank order of numbers. Infracommunities in Podiceps auritus overlapped those of the other two species of Podiceps and had few (2) core species. Most (11 of 14) core species are specialists in grebes, but only one was limited to a single host species. Most were shared among hosts, with the bulk of the population of each occurring in one host species. Sharing was particularly significant between the large, fish-eating grebes (A. occidentalis and P. grisegena) and between the smaller, mainly invertebrate-eating grebes (P. nigricollis and P. auritus). Host specificity and the pattern of exchange of helminths, mediated by the differentiated but overlapping host food habits, were important determinants of enteric helminth community structure.