The angle of repose: Facilitation and its effects on the Brachypodium distachyon grass complex

Plant communities are a complex web of interactions which may harbor inherent resilience to environmental stressors. One means of coping with changing conditions may be interspecific facilitation, a process in which neighboring perennial plants positively influence spatially associated annual species, especially in harsh conditions. However, the details of the effect of interspecific facilitation on ecotypic variation and population structure of annual grasses are largely unknown. In order to gain more insight into the ecological and evolutionary dynamics of annual grasses, I investigated whether neighboring perennial plants affect the occurrence, morphological traits, genetic substructure and intergenerational trait retention of the annual grass Brachypodium. Although I did not find a strong association of Brachypodium with neighboring perennial plants as aridity increases, I did find that Brachypodium occurring underneath canopy cover resulted in higher seed production and taller plants than those found in open patches in wild populations. Although my genotypic data did not find evidence that neighboring perennial plants strongly affect the genetic substructure, in my final experiment, as a main result, I found that both the number of seeds and the seed weight were significantly higher if the grandparental location of origin was underneath perennial plant cover. These results indicate that the microhabitat as provided by neighboring perennial plants can potentially affect fitness in Brachypodium and influence ecotypic variation at the microscale. Although the mechanism behind these facilitative effects is unknown, these findings indicate that facilitation may play a larger role and have more influence on plant community dynamics than previously anticipated.