| Summary: | Dissertation submitted in partial fulfillment of a Philosophiae Doctor degree in Biology The parasite fauna of the Icelandic rock ptarmigan Lagopus muta had just been described when engaging in this project in 2010. Purpose was to study the influence that parasites exhibit on ptarmigan population change over a period of 7 years (2006–2012). The cycles that the Icelandic ptarmigan population has recently been undergoing peak every 5–6 years. Host-parasite interactions are known as one possible regulator of cycling host populations. Measures of the parasite community and pathogenic parasites were analysed. Ptarmigan population density was particularly associated with the prevalence of a coccidian parasite named Eimeria muta. Annual aggregation levels of this eimerid fluctuated inversely with its prevalence, with lows at prevalence peak and vice versa. Both prevalence and aggregation of E. muta tracked ptarmigan population density with a 1.5 year time lag. The time lag could be explained by the host specificity of this eimerid, host density dependent shedding of oocysts, and their persistence in the environment from one year to the next. E. muta prevalence was also negatively associated with ptarmigan body condition, marginally negatively with fecundity, and positively with mortality, indicating their pathogenicity. Further, there were significant associations between fecundity and the chewing louse Amyrsidea lagopi prevalence (negative), excess juvenile mortality and the nematode Capillaria caudinflata prevalence (positive), and adult mortality and the skin mite Metamicrolichus islandicus prevalence (negative). Though this study is correlational, it provides strong evidence that the microparasite E. muta has the potential to destabilize rock ptarmigan population dynamics in Iceland. Sníkjudýrafánu íslensku rjúpunnar Lagopus muta hafði nýlega verið lýst þegar rannsóknir mínar hófust árið 2010. Markmið mitt var að rannsaka hvaða áhrif sníkjudýr hafa á stofnbreytingar rjúpunnar og rannsóknatíminn var 7 ár ...
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