Invasive amphibians alter host-pathogen interactions with primarily negative outcomes for native species

Invasive species can influence host-pathogen dynamics through a variety of mechanisms, potentially exacerbating or ameliorating disease consequences for native species. Pathogenic infections influence amphibian population and community dynamics worldwide, to the extent that community composition is often structured by host-pathogen interactions. Multiple amphibian species have also invaded new environments globally, causing direct and potential indirect impacts on host and pathogen community composition. To synthesize knowledge on the consequences of invasive amphibians interacting with pathogens in novel environments, we systematically reviewed the current literature and quantified how invasive amphibian species alter disease dynamics within amphibian communities. Overall, we found 145 studies that assessed pathogen impacts of amphibian invasions. Of those, 110 documented invasion-facilitated disease amplification (IDA), where amphibian invaders increased pathogen diversity, prevalence, infection intensity, or decreased host fitness from pathogen infections. In contrast, 17 studies found no change on pathogens in the native community when an invasive amphibian arrived, and 19 studies documented invasion-facilitated disease reduction (IDR) in the resident amphibian community, where invasive species decreased negative pathogen impacts to native species. Thus, IDA was more common, and the magnitude of IDA effects was also larger than the minimal IDR effects observed. Finally, we identified gaps in the current literature and suggest management actions that may help to protect native amphibians from these negative interactions. Enhancing our knowledge of how invasive amphibian species interact with pathogens will improve the response to ongoing and future invasions in an era of global change that continues to drastically reduce global amphibian biodiversity.