Submitted to: International Symposium on Microbiology of Aerial Plant Surfaces
Publication Type: Abstract Only
Publication Acceptance Date: 9/8/1995
Publication Date: N/A
Technical Abstract: We investigated the relationship between competitive ability and fitness of epiphytic microbes using two approaches. First, we developed a model to quantify competitive abilities of coexisting microorganisms on leaves independently of their population densities, and we used the model to determine effects of competition on fitness components as a function of population density. Second, we used Weldon and Slauson's (1986) method to distinguish the intensity of competition from its importance to fitness. We determined population density relative to initial inoculum density on wheat leaves for strains of an obligate fungal parasite Puccinia graminis f.sp. tritici and for bacterial epiphytes Pseudomonas syringae and Stentrophomonas maltophilia. In each experiment, the effect of competition was determined by comparing single strain or species inoculations with mixed inoculations at the same inoculum density. In conjunction with the two models, we used the data from these experiments with a wide range of initial inoculum densities to investigate the relationship between competitive ability and fitness. The experimental results and the models show that it is possible for poorer competitors to be more fit than better competitors both in the presence and in the absence of the competitor. When physical factors predominantly determine variability in population sizes, the relative importance of competition will be small. On the other hand, the importance of competition to fitness will be very great in situations in which there are few other sources of population variance.