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.