Identifying knowledge gaps about context dependency in freshwater species invasions

The abiotic template of freshwater ecosystems is being altered by human activity on a global scale, often promoting the establishment of new invasive taxa and increasing the likelihood of facilitation between invaders. These positive interactions represent a substantive threat to freshwater ecosystems by promoting the establishment and persistence of invasive taxa. To assess the threat posed by freshwater invasive species under global change, we leveraged the existing literature at the intersection of freshwater invasive species and positive biotic interactions using systematic review and meta‐analysis. Our findings revealed critical knowledge gaps in the study of interactions between invasive taxa which may lead to an underestimation of their threat. These gaps included a lack of studies that address indirect interactions, particularly over long temporal scales. Such interactions were understudied for invasive taxa but were often strongly positive. Additionally, almost a third of the publications examined documented context dependent interactions, but only a single publication did so between invasive organisms. Common forms of anthropogenic change, including alterations to habitat quality, nutrient availability, and hydrology, were among the most frequent drivers of context dependency. Our analysis supports the conclusion that 1) the threat of facilitation between freshwater invaders may be underestimated by the current literature, and 2) global change may drive context dependent interactions between freshwater invasive species, but there is a lack of research addressing this possibility.