Foliar pathogen increase, not competitive release, mediates reduced invasibility following biodiversity loss

Classic theory posits that biodiversity loss increases community invasibility via competitive release. We demonstrate instead that species loss reduces invasibility by intensifying foliar fungal diseases. This pathogen-mediated suppression creates a powerful biotic filter that overrides competitive release, revealing biodiversity's dual role in maintaining community stability through both competitive and disease-mediated resistance. Our findings necessitate integrating disease ecology into our understanding of how biodiversity loss impacts ecosystem resilience.