Abstract
Abstract Global warming challenges the persistence of local populations, not only through heat‐induced stress, but also through indirect biotic changes. We study the interactive effects of temperature, competition and parasitism in the water flea Daphnia magna. We carried out a common garden experiment monitoring the dynamics of Daphnia populations along a temperature gradient. Halfway through the experiment, all populations became infected with the ectoparasite Amoebidium parasiticum, enabling us to study the interactive effects of temperature and parasite dynamics. We combined Integral Projection Models with epidemiological models, parameterized using the experimental data on the performance of individuals within dynamic populations. This enabled us to quantify the contribution of different vital rates and epidemiological parameters to population fitness across temperatures and Daphnia clones originating from two latitudes. Interactions between temperature and parasitism shaped competition, where Belgian clones performed better under infection than Norwegian clones. Infected Daphnia populations performed better at higher than at lower temperatures, mainly due to an increased host capability of reducing parasite loads. Temperature strongly affected individual vital rates, but effects largely cancelled out on a population‐level. In contrast, parasitism strongly reduced fitness through consistent negative effects on all vital rates. As a result, temperature‐mediated parasitism was more important than the direct effects of temperature in shaping population dynamics. Both the outcome of the competition treatments and the observed extinction patterns support our modelling results. Our study highlights that shifts in biotic interactions can be equally or more important for responses to warming than direct physiological effects of warming, emphasizing that we need to include such interactions in our studies to predict the competitive ability of natural populations experiencing global warming. A free Plain Language Summary can be found within the Supporting Information of this article.
Highlights
Climate change challenges the persistence of local populations (Bellard et al, 2012)
All populations became infected with the ectoparasite Amoebidium parasiticum, enabling us to study the interactive effects of temperature and parasite dynamics
These immigrants could potentially out-compete local populations, their success will depend on the evolutionary potential of the resident population (Van Doorslaer, Vanoverbeke, et al, 2009) and the degree to which immigrant genotypes are adapted to local environmental conditions (De Meester et al, 2018)
Summary
Climate change challenges the persistence of local populations (Bellard et al, 2012). Temperature alters host–parasite interactions, both through interactive effects of temperature and parasitism on host performance (Greenspan et al, 2017; Hector et al, 2019; Padfield et al, 2020), as well as through temperature effects on parasite dynamics themselves (Cohen et al, 2019; Gehman et al, 2018; Morley & Lewis, 2014) Depending on how these thermal effects play out in a specific system, where both hosts and their parasites typically show unimodal responses to temperature (Dell et al, 2011; Kirk et al, 2018; Mordecai et al, 2019; Shocket et al, 2019), infections may become more prevalent and more severe under climate change in some systems (Altizer et al, 2013; Hall et al, 2006; Harvell et al, 2002; Lafferty, 2009; Lafferty & Mordecai, 2016; Mouritsen et al, 2005). These immigrants could potentially out-compete local populations, their success will depend on the evolutionary potential of the resident population (Van Doorslaer, Vanoverbeke, et al, 2009) and the degree to which immigrant genotypes are adapted to local environmental conditions (De Meester et al, 2018)
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