Deforestation rates of tropical forests have led to a massive increase in forest edge habitats globally. One of the foremost fragmentation types of concern is agriculture, which can introduce new pathogenic fungi into tropical forests via spillover. The long-term effects these spillovers will have on tropical forests are largely unknown but have the potential to influence overall community diversity. This study utilizes both a theoretical model that uses a modified Lotka-Volterra equation and an empirical study in Costa Rican forests to investigate how pathogenic fungal spillover will affect tree seedling diversity. Theoretically, spillover had various effects on plants, depending on a species’ competitive strength, palatability to the pathogen, and overall pathogen strength. In all cases, coexistence of species was inhibited by spillover at the forest edge, however it promoted more instances of coexistence at the interior and rescued weaker plant species when targetting the superior competitor. The study in Costa Rica found that fungal pathogens had no effect on survival but varying effects on overall diversity. This indicates that fungal spillover has the potential to weaken or strengthen mechanisms driving diversity and may be forest-specific, no longer defined by traditional diversity hypotheses. Overall, this study highlights the importance of understanding the effects of fungal spillover and how it may potentially influence the growth and survival of tree seedlings in fragmented tropical forests across the globe
