ECOLOGICAL AND EVOLUTIONARY DRIVERS OF SPECIES DISTRIBUTIONS IN THE GRASSY BIOME

Research Problem: A biome is a functionally distinct collection of vegetation that occurs according to climatic and soil conditions. For example, rainforests and tropical grasslands should occur in different climates and are expected to differ drastically in their biogeochemical rates, owing to differences in plant water-use, nutrient-use, and photosynthesis. Therefore, global change is anticipated to further modify biome distributions and contribute further to biogeochemical cycling. However, with increased theoretical attention and availability of global datasets (e.g., remote sensing, trait consortiums) there is a growing awareness of climate disequilibrium in vegetation and the important and interacting roles of disturbance, phylogenetic history, biogeographic historical contingency, and local community processes. It appears that these processes contribute considerably to within- and among-biome differences in vegetation functioning and distribution (Chapter I). This dissertation provides a multi-scale, empirical investigation of the factors contributing to the distribution of grasses. Methods: The local and landscape scale experiments were conducted in the Serengeti Ecosystem of East Africa, a savanna with an intact, natural disturbance regime. In xix Serengeti, I investigated the role of herbivores, soil, and climate interactions for influencing species distributions with a combination of greenhouse manipulation (Chapter II), field observation (Chapter III), analysis of trait evolution (Chapter IV), and an analysis of the consequence of these processes on community structure (Chapter V). Furthermore, I compare the results from Serengeti to other communities globally (Chapter V). In order to transition to a regional scale, focus is shifted to North America, where there are detailed vegetation plot data on a continental scale (Chapter VI). Finally, to ask about grass distributions at a global scale I analyze historical vegetation maps from grassy ecosystems across the world (Chapter VII). Conclusions: Altogether, the results of the studies reported here demonstrate a pervasive and multi-scale need to consider plant lineage and biotic-abiotic interactions in distribution models (Chapter VIII). The results from Serengeti suggest that species have fundamental differences in their responses to combined soil sodium and defoliation, ranging from herbivore tolerant species that cannot tolerate sodium to those that tolerate high soil sodium but cannot withstand simultaneous herbivory. This contributes to the distribution of herbaceous community composition in Serengeti, and is one of many processes contributing to the appearance of species aggregations and a convergent pattern of trait evolution. These processes were qualitatively similar to those contributing to the distribution of grass functional types and lineages at regional and global scales, where climate and soils were not adequate to explain grass distributions.

Grantor dc:publisher

Wake Forest University

Year dc:date.issued

2016

Author dc:creator

• Griffith, Daniel Mark

• community ecology

Language dc:language.iso

en

Handle dc:identifier.uri

http://hdl.handle.net/10339/59301

OAI identifier oai:identifier

oai:wakespace.lib.wfu.edu:10339/59301