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Abstract Freshwater ecosystems can serve as model systems that reveal insights into biological invasions. In this article, we summarize nine lessons about aquatic invasive species from the North Temperate Lakes Long-Term Ecological Research program and affiliated projects. The lessons about aquatic invasive species are as follows: Invasive species are more widespread than has been documented; they are usually at low abundance; they can irrupt from low-density populations in response to environmental triggers; they can occasionally have enormous and far-reaching impacts; they can affect microbial communities; reservoirs act as invasive species hotspots; ecosystem vulnerability to invasion can be estimated; invasive species removal can produce long-term benefits; and the impacts of invasive species control may be greater than the impacts of the invasive species. This synthesis highlights how long-term research on a freshwater landscape can advance our understanding of invasions. 

Abstract Batrachochytrium dendrobatidis(Bd), an aquatic pathogenic fungus, is responsible for the decline of hundreds of amphibian species worldwide and negatively impacts biodiversity globally. Prophylactic exposure to the metabolites produced by Bd can provide protection for naïve tree frogs and reduce subsequent Bd infection intensity.Here, we used a response surface design crossing Bd metabolite prophylaxis concentration and exposure duration to determine how these factors modulate prophylactic protection against Bd in Pacific chorus frog (Pseudacris regilla) tadpoles (5 × 5 surface design) and metamorphs (3 × 3 surface design). We exposed individuals every weekday to one of five Bd metabolite concentrations or a water control for 1–5 weeks, after which all animals were challenged with live Bd to evaluate their susceptibility.Exposure to the Bd metabolite prophylaxis reduced Bd load and prevalence compared to the control for both the tadpoles and metamorphs. Increasing Bd metabolite prophylaxis concentration did not confer additional protection for either life stage, but increasing duration of exposure did benefit metamorphs by decreasing Bd prevalence but not Bd load.On average, control tadpoles and metamorphs had 66.2% and 99.4% higher Bd loads, respectively, than tadpoles and metamorphs exposed to any Bd metabolite prophylaxis.Additionally, Bd metabolite prophylaxis reduced Bd prevalence relative to controls in both tadpoles (20.5% vs. 56.3%, respectively) and metamorphs (21.9% vs. 87.5%, respectively).Synthesis and applications: The efficacy of short‐term exposures of relatively low concentrations of Bd metabolites at reducing Bd infections suggests that this approach has the potential to be scaled up to field use to aid in disease mitigation and conservation. Our results, combined with additional research on Bd metabolite prophylaxis for other amphibian species, suggest that this strategy may represent a broadly useful tool to protect at‐risk amphibian populations. 

Abstract Landscapes of fear can determine the dynamics of entire ecosystems. In response to perceived predation risk, prey can show physiological, behavioral, or morphological trait changes to avoid predation. This in turn can indirectly affect other species by modifying species interactions (e.g., altered feeding), with knock‐on effects, such as trophic cascades, on the wider ecosystem. While such indirect effects stemming from the fear of predation have received extensive attention for herbivore–plant and predator–prey interactions, much less is known about how they alter parasite–host interactions and wildlife diseases. In this synthesis, we present a conceptual framework for how predation risk—as perceived by organisms that serve as hosts—can affect parasite–host interactions, with implications for infectious disease dynamics. By basing our approach on recent conceptual advances with respect to predation risk effects, we aim to expand this general framework to include parasite–host interactions and diseases. We further identify pathways through which parasite–host interactions can be affected, for example, through altered parasite avoidance behavior or tolerance of hosts to infections, and discuss the wider relevance of predation risk for parasite and host populations, including heuristic projections to population‐level dynamics. Finally, we highlight the current unknowns, specifically the quantitative links from individual‐level processes to population dynamics and community structure, and emphasize approaches to address these knowledge gaps. 

Abstract There is a rich literature highlighting that pathogens are generally better adapted to infect local than novel hosts, and a separate seemingly contradictory literature indicating that novel pathogens pose the greatest threat to biodiversity and public health. Here, usingBatrachochytrium dendrobatidis, the fungus associated with worldwide amphibian declines, we test the hypothesis that there is enough variance in “novel” (quantified by geographic and phylogenetic distance) host‐pathogen outcomes to pose substantial risk of pathogen introductions despite local adaptation being common. Our continental‐scale common garden experiment and global‐scale meta‐analysis demonstrate that local amphibian‐fungal interactions result in higher pathogen prevalence, pathogen growth, and host mortality, but novel interactions led to variable consequences with especially virulent host‐pathogen combinations still occurring. Thus, while most pathogen introductions are benign, enough variance exists in novel host‐pathogen outcomes that moving organisms around the planet greatly increases the chance of pathogen introductions causing profound harm.