Understanding assembly of low-diversity plant communities within hyperdiverse ecosystems

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Carrie A. Barker, Biological Sciences, Louisiana State University, Baton Rouge, LA and Kyle Harms, Department of Biological Sciences, Louisiana State University, Baton Rouge, LA

Background/Question/Methods
Assembly of plant communities is a key topic in ecology, as the specific mechanisms acting on assembly determine the level of diversity within a community. Studying low-diversity areas within high-diversity communities has the potential to disentangle the mechanisms operating within high-diversity communities. Mechanisms occurring within low-diversity areas must be absent in high-diversity areas. Two ecosystems with characteristically high species diversity are sub-tropical pine savannas and tropical forests. Longleaf pine savannas in the southeastern United States are extremely diverse even though the understory is dominated by bunchgrasses. In some areas where bunchgrasses are absent, the understory is dominated by clonal species like bracken fern (Pteridium aquilinum) and gallberry (Ilex glabra). Tropical forests are considered the most species-rich terrestrial communities on the planet, yet patches dominated by understory ferns such as Polybotrya caudata can be found within them. My objective was to determine whether diversity is lower within these patches compared to the diversity outside of these patches. I measured diversity in terms of species richness and abundance within monodominant patches as well as outside of the patches at field sites in Camp Whispering Pines, Louisiana and La Selva Biological Station, Costa Rica.
Results/Conclusions
I found that species richness was lower by 53% and 121% and abundance lower by 21% and 195% in the bracken fern and gallberry patches, respectively, compared to the diversity within the bunchgrass areas. This pattern of lower diversity was also seen within the fern patches in Costa Rica. Species richness was lower by 109% and abundance lower by 251% compared to outside of the fern patches. Further measurements of diversity for a more complete picture are yet to come. Diversity is lower within the monodominant patches even though, in Louisiana specifically, an understory dominated by bunchgrasses is able to support high levels of diversity. In future research I will look at the mechanisms causing the lower diversity within these patches. Understanding the mechanisms operating at levels of low diversity can help us better understand mechanisms operating at levels of high diversity, as those present in one must be absent in the other. These results could also be applied to other clonal species such as invasive species to help with restoration efforts.