When our roommates or family members get sick, we try to keep our distance and avoid catching their illness. Plants get ‘sick’ too, and in the natural world, this may actually explain the coexistence and diversity of plant species that we see.

Coexistence

Species coexistence relies on competition between individuals of the same species being larger than competition between individuals of different species. Competition between individuals of the same species must be large enough to keep any species from taking over and outcompeting all other species in the community. However, more recent work has highlighted the role of natural pathogens. Stable coexistence of many species may be favored if individuals of one species cannot live in close proximity to each other due to disease.

Plant Pathogens and Biodiversity

View looking south from the canopy tower at the Gamboa Rainforest Resort over the confluence of the Panama Canal and the Chagres River near Gamboa, Panama.

For example, picture a crowded forest with many adult trees of the same species releasing wind-dispersed seeds (like the helicoptering seeds of a maple). Very few, if any, of the seeds that fall near to the adult trees will germinate and reach maturity. As you walk away from the clump of adult trees, you will begin to find more germinated seeds that reach maturity (Augspurger 1983). These seeds are farther from tough competitors of the same species (adult trees) and are away from the plant pathogens that may be living in the adult root system. In our hypothetical forest, the plant pathogens that feed on young maples are keeping maple from dominating the forest, allowing other species that aren’t affected by the pathogen to thrive; in this way, plant pathogens play a role in the maintenance of biodiversity.

Drivers of Biodiversity

Our guest this week, Tyler Schappe, studies interactions among plants and fungi in the Neotropical forests of Panama. Tyler is broadly interested in what drives the maintenance and diversity of fungal communities, and how this, in turn, can affect tree communities. Tyler spent the summer of 2015 collecting 75 soil cores from three forest plots in Panama. Using DNA sequencing with universal genetic markers, he was then able to identify the fungi within the soil cores to species and functional group (decomposers, pathogens, plant mutualists, etc.). So far, Tyler has found that tree communities and soil nutrients affect the composition and diversity of fungal guilds differently. As expected, guilds that form mutualistic relationships with trees are more strongly correlated with plant communities. Interestingly, soil properties influence the species composition of all fungal guilds, including plant pathogens, pointing to the mediating role of soils as an abiotic filter. Overall, Tyler’s results, along with other research, show that soil fungal communities are an integral component of the plant-soil relationship since they are driven by, and can affect, both. Together, plants, soil, and fungi form a tightly connected three-way relationship, and wanting to understand one of them means having to study all three together.

Tyler’s work with fungal communities in Panama sheds light on belowground interactions and their implications for plant ecology. His research is one piece of evidence that may help us to understand why there are so many plant species, how they coexist, and why some species are common and some are rare. Are plant pathogens significant contributors to species richness and biodiversity? If so, what modulates plant pathogens, and how can that indirectly affect tree communities? To find out more about Tyler’s work check out these two sources from the Journal of Ecology and Science.

Spend sugar to make sugar

Stand of bur oak trees in a remnant oak savanna at Pheasant Branch Conservancy near Middleton, WI in early winter.

At a young age, Tyler began to realize how connected the world was and how plants and animals function in an ecosystem. The functioning of organisms and of ecosystems came into focus for him while in college at University of Wisconsin-Madison. He took a course in plant ecology from Dr. Tom Givnish who described plants in terms of economic trade-offs. For example, energy invested by plants in vertical growth cannot be invested in defense or reproduction; different allocations of resources can be more or less advantageous in different environments. Tyler decided to pursue graduate school at Oregon State while completing a fellowship with the Smithsonian Tropical Research Institute in Panama, where he met his current advisor, Andy Jones.

Tyler is defending his Master’s thesis August, 29 2017!  We are glad he can make time to talk with us on Inspiration Dissemination this Sunday August, 13 at 7 pm. Not a local listener? Stream the show live!