Oklahoma State University Stillwater, OK, United States
Background/Question/Methods
Tropical forests are the most biodiverse ecosystems in the world and are critical to global ecosystem functions. Human-mediated disturbance has increased forest fragmentation, yet the effects of fragmentation on the mechanisms maintaining high tropical tree diversity are widely unknown. Fragmentation by agricultural expansion has the potential to introduce new interactions into tropical forests via spillover, particularly transmission of pathogenic fungi, which can influence species diversity. To investigate the effects of spillover on tropical forest communities, we created a theoretical model representing plant species coexisting via the effect of a predator, (e.g. herbivore or pathogen), and introduced exposure to fungal pathogen spillover. We aimed to test how plant coexistence would be altered by pathogen spillover and how host-specificity of the introduced pathogen would influence coexistence outcomes. Theory about fungal pathogen spillover has focused on transmission dynamics and less on the impacts on host community composition. Despite this gap, studies have shown that fungal pathogen spillover can greatly influence plant community composition and diversity. Therefore, there is a need to bridge theories of species coexistence and spillover. We created a Lotka-Volterra one-predator two-prey model with a type two functional response, found coexistence, and then introduced new predator spillover using a diffusion equation.
Results/Conclusions
Preliminary models provide predictions into the response of plant populations to the introduction of pathogenic fungal spillover in tropical forests. Once pathogen spillover is introduced into the predator-prey system, it creates a drastic shift in species composition and negatively impacts coexistence. This is important because it indicates the sensitivity of plant populations to changes in ecosystem dynamics. The model also shows that it is possible for plant populations to coexist under both a predator and spillover but only if spillover occurs at very low rates as expected in the forest interior. Host-specificity of the introduced pathogen also strongly influenced plant coexistence. If the introduced pathogen preferentially targets the common plant species, coexistence is conserved (or even promoted in some scenarios). In contrast, if the introduced pathogen targets the rare plant species, it can lead to extinction. In the field, it is unknown how much fungi are spilling over into nearby forests, so this model can provide insight for what to expect plant community composition and diversity to be dependent on spillover rate and host-specificity.
