How strong is enemy release? A systematic compilation across taxa and approaches

Area of Science:

• Ecology
• Invasive Species Biology
• Biogeography

Background:

• The enemy release hypothesis suggests invasive species escape natural enemies in new ranges.
• Understanding enemy release is crucial for predicting invasive species success and managing biocontrol.

Purpose of the Study:

• To systematically review and quantify enemy release across diverse taxa and ecosystems.
• To assess the impact of enemy release on invasive species fitness and identify factors influencing its strength.

Main Methods:

• Conducted a systematic review of 691 enemy release contrasts from global aquatic and terrestrial systems.
• Analyzed biogeographic contrasts (native vs. introduced range) and community contrasts (native vs. introduced species).
• Examined enemy diversity, enemy damage, and host fitness metrics.

Main Results:

• Introduced species experienced significantly lower enemy pressure (43% in biogeographic, 70% in community contrasts).
• One-third of cases showed higher enemy pressure in the introduced range.
• Enemy release was linked to reduced enemy diversity and damage, but not consistently to increased host fitness.
• Biogeographic enemy release varied by taxon, being higher in mollusks and fish, lower in insects and algae.

Conclusions:

• Enemy release is a common phenomenon but its impact on invasive species fitness is variable.
• Reduced enemy pressure does not always confer a fitness advantage.
• Understanding taxon-specific enemy release can inform biocontrol strategies and invasive species management.