Differences in Disease Incidence Across Species Richness and Phylogenetic Dispersion Gradients

Background/Question/Methods

: This project assesses the differences in disease incidence across plant species richness and phylogenetic dispersion gradients. Diversity acts as a buffer, as disease is caused by bacteria and fungi which are typically family and species-specific. Pathogens are specialists, so we would assume plots that are under-dispersed will be affected more than those with variety. We expect to see a dilution of pathogens when there is a higher variety of species due to plant diversity. This project poses the question, how does the level of disease incidence measured change depending on whether the plants are over-dispersed or under-dispersed? In order to answer this question, we manipulated species richness and plant phylogenetic diversity on 240 plots. These plots contained plants from three different families each containing six different species, resulting in 18 species. The plots had different combinations of species as well as under and over-dispersion of families. We randomly selected 8 individual plants per species and recorded the disease seen using a 1-10 scale in each plot. We then conducted an analysis of variance to assess planting effects on disease incidence in response to the experimental design.

Results/Conclusions

: The results show that the plant species richness factor is significant. We found that disease incidence decreased as plant species richness increased (Eupatorium altissimum p-value = 0.015, Silphium integrifolium p-value = 0.054, Dalea candida p-value = 0.039, Desmodium canadense p-value = 0.001, Andropogon gerardii p-value = 0.056). We also found that plants in plots that were phylogenetically over-dispersed had lower concentrations of disease (E. altissimum p-value = 0.005, S. integrifolium p-value = 0.003, Echinacea pallida p-value = 6.55e-07, Dalea purpurea p-value = 0.001, Liatris pynostachya p-value = 0.0007). Our findings provide evidence to support the dilution effect, as well as the concept of pathogen accumulation in low species richness. This evidence supports the idea that host availability as well as pathogen specialization, is what influences the amount of disease incidence found in plants. This information provides insight into the role of resident microbial pathogens in native plant community diversity maintenance, which is accumulating consideration in novel restoration and conservation efforts. This information gives hope that “a change is gonna come”.