Microhabitat preference and coexistence of ectoparasitic arthropods on Alaskan seabirds

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Abstract
The population structure and distribution patterns of ectoparasitic arthropods on four species of Alaskan seabirds (common murre (Uria aalge), thick-billed murre (Uria lomvia), black-legged kittiwake (Rissa tridactyla), and red-legged kittiwake (Rissa brevirostris)) were studied and interspecific interactions were examined. In most ectoparasite populations on murres and kittiwakes, females predominated. This pattern may be attributable to differences in activity, behavior, and mortality between the sexes of the ectoparasites. Except for feather mites, adults of most ectoparasites were less abundant than immatures. The extremely high relative abundance of immature ticks was probably due to the high fecundity of these organisms and predation pressure. Distribution patterns of adults differed significantly from those of immatures in most louse and tick populations. Populations of lice (Quadraceps obliquus (Mjöberg), Quadraceps ornatus (Grube)) and ticks (Ixodes uriae White) on murres and kittiwakes were highly clumped. The degree of clumping was lower among ectoparasites on murres than among those on kittiwakes. Murres aggregate more and thus provide more opportunities for their ectoparasites to disperse to new host individuals. Ticks were the dominant group of ectoparasites in most body regions. On the wings, however, mites were much more abundant. The wings provided the largest surface area and supported the highest ectoparasite species diversity and population density. The louse and tick populations exhibited distinct patterns of spatial distribution on the host, largely as a result of their distinct preferences for certain microhabitats. However, close competition appears to occur between Q. obliquus and I. uriae on murres, and between the two feather mites, Alloptes (Alloptes) sp. and Laronyssus martini (Trouessart), on kittiwakes.