Evaluating unintended consequences of intentional species introductions and eradications for improved conservation management.

Conservation management is deploying increasingly intensive strategies to maintain biodiversity and ecosystem function in response to global anthropogenic threats. These strategies include intentionally introducing and eradicating species around the world via assisted migration, rewilding, biological control, invasive species eradications, and gene drives - management actions which have become highly contentious because of their potential for unintended consequences. We conducted a global literature review of these conservation actions to quantify how often unintended outcomes occur and to elucidate their underlying causes. We found that studies reported intended outcomes in 51% of cases, a combination of intended outcomes and unintended outcomes in 26% of cases, and strictly unintended outcomes in 10% of cases. Hence, unintended outcomes were reported in 36% of all cases evaluated. In evaluating overall conservations outcomes (weighing intended vs unintended effects), some unintended effects are fairly innocuous relative to successful conservation objectives whereas others result in serious unintended consequences in recipient communities. Importantly, we also found that studies that assessed a greater number of community interactions with the target species were more likely to report unintended outcomes, suggesting that unintended consequences may be under-reported due to insufficient vetting. Most reported unintended outcomes arose from direct effects (68%) or simple density-mediated, indirect effects (25%) linked to the target species, with only a few documented cases arising from more complex interaction pathways (7%). Therefore, most unintended outcomes involved simple interactions that could potentially be predicted and mitigated through more formal vetting. To address this shortfall, we applied foundational concepts from community ecology to develop a community assessment framework which can be used to systematically screen for potential impacts on nontarget species prior to implementing conservation actions. We propose that incorporating this approach to screen proposed conservation actions could help reduce unintended consequences from intentional species introductions and eradications for conservation. This article is protected by copyright. All rights reserved.