Abstract
The enemy release hypothesis (ERH) is the best-known hypothesis
explaining high performance (e.g., rapid population growth) of exotic
species. However, the current framing of the ERH does not explicitly
link evidence of enemy release with exotic performance. This leads to
uncertainty regarding the role of enemy release in biological invasions.
Here we demonstrate that the effect of enemy release on exotic
performance is the product of three factors: enemy impact, enemy
diversity, and host adaptation. These factors are modulated by seven
contexts: time since introduction, resource availability, phylogenetic
relatedness of exotic and native species, host-enemy asynchronicity,
number of introduction events, type of enemy, and strength of
growth-defence trade-offs. ERH-focused studies frequently test different
factors under different contexts, leading to inconsistent findings,
which characterise current evidence for the ERH. For example, over 80%
of meta-analyses fail to consider ecological contexts that can modulate
study findings; we demonstrate this by re-analysing a recent ERH
synthesis. Structuring the ERH around factors and contexts promotes
generalisable predictions about when and where exotic species may
benefit from enemy release, empowering effective management. Our
mechanistic factor-context framework clearly lays out the evidence
required to support the ERH, unifies many enemy-related invasion
hypotheses and enhances predictive capacity.