Abstract
Climate change is expected to modify host-parasite interactions which is concerning because parasites are involved in most food-web links, and parasites have important influences on the structure, productivity and stability of communities and ecosystems. However, the impact of climate change on host–parasite interactions and any cascading effects on other ecosystem processes has received relatively little empirical attention. We assessed host-parasite dynamics for moose (Alces alces) and winter ticks (Dermacentor albipictus) in Isle Royale National Park over a 19-year period. Specifically, we monitored annual tick burdens for moose (estimated from hair loss) and assessed how it covaried with several aspects of seasonal climate, and non-climatic factors, such as moose density, predation on hosts by wolves (Canis lupus) and wolf abundance. Summer temperatures explained half the interannual variance in tick burden with tick burden being greater following hotter summers, presumably because warmer temperatures accelerate the development of tick eggs and increase egg survival. That finding is consistent with the general expectation that warmer temperatures may promote higher parasite burdens. However, summer temperatures are warming less rapidly than other seasons across most regions of North America. Therefore, tick burdens seem to be primarily associated with an aspect of climate that is currently exhibiting a lower rate of change. Tick burdens were also positively correlated with predation rate, which could be due to moose exhibiting risk-sensitive habitat selection (in years when predation risk is high) in such a manner as to increases the encounter rate with questing tick larvae in autumn. However, that positive correlation could also arise if high parasite burdens make moose more vulnerable to predators or because of some other density-dependent process (given that predation rate and moose density are highly correlated). Overall, these results provide valuable insights about interrelationships among climate, parasites, host/prey, and predators.
Highlights
IntroductionClimate change influences organisms directly (i.e., by influencing physiology and behavior) and indirectly by modifying trophic interactions, such as consumer-resource relationships (Ottersen et al, 2001; Stenseth et al, 2002; Walther et al, 2002)
Climate change influences organisms directly and indirectly by modifying trophic interactions, such as consumer-resource relationships (Ottersen et al, 2001; Stenseth et al, 2002; Walther et al, 2002)
New host-parasite relationships seem likely to form as species shift their geographic ranges in response to climate change and some host species will be exposed to parasites to which they have no immunity or coevolutionary history (Brooks and Hoberg, 2007)
Summary
Climate change influences organisms directly (i.e., by influencing physiology and behavior) and indirectly by modifying trophic interactions, such as consumer-resource relationships (Ottersen et al, 2001; Stenseth et al, 2002; Walther et al, 2002). Warming temperatures could favor earlier emergence dates, faster development, increased survival, and extended periods of activity for many parasite species (Ogden et al, 2006; Poulin, 2006; Calero-Torralbo et al, 2013). For those reasons, climate change is generally expected to favor parasites over hosts with more severe effects of parasites predicted in the future (Patz et al, 2003; Pounds et al, 2006; Barber et al, 2016). Any such impacts of climate change on host-parasite relationships are likely to be substantial and widespread because parasites account for a large portion of the world’s biodiversity (Dobson et al, 2008; Kuris et al, 2008) and are involved in the majority of food-web links (Lafferty et al, 2006; Dunne et al, 2013)
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