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| Host-parasite systems can be powerful arenas in which to explore factors influencing
community structure. We used a comparative approach to examine the influence of
host ecology and morphology on the diversity of chewing lice (Insecta: Phthiraptera)
among 52 species of Peruvian birds. For each host species we calculated two
components of parasite diversity: 1) cumulative species richness, and 2) mean
abundance. We tested for correlations between these parasite indices and 13 host
ecological and morphological variables. Host ecological variables included geographic
range size, local population density, and microhabitat use. Host morphological
variables included body mass, plumage depth, and standard dimensions of bill,
foot and toenail morphology, all of which could influence the efficiency of anti-parasite
grooming. Data were analysed using statistical and comparative methods that
control for sampling effort and host phylogeny. None of the independent host
variables correlated with louse species richness when treated as a dependent variable.
When richness was treated as an independent variable, however, it was positively
correlated with mean louse abundance. Host body mass was also positively correlated
with mean louse abundance. When louse richness and host body mass were held
constant, mean louse abundance correlated negatiely with the degree to which the
upper mandible of the host’s bill overhangs the lower mandible. This correlation
suggests that birds with longer overhangs are better at controlling lice during
preening. We propose a specific functional hypothesis in which preening damages lice
by exerting a shearing force between the overhang and the tip of the lower mandible.
This study is the first to suggest a parasite-control function of such a detailed
component of bill morphology across species. Avian biologists have traditionally
focused almost exclusively on bills as tools for feeding. We suggest that the adaptive
radiation of bill morphology should be reinterpreted with both preening and feeding
in mind. | |
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