Data from: Density-dependent disease, life history tradeoffs, and the effect of leaf pathogens on a suite of co-occurring close relatives

1. Plant pathogens reduce the performance of their hosts and therefore may contribute to ecological mechanisms of coexistence. In Chesson’s framework, pathogens contribute to stabilizing mechanisms when they intensify negative intraspecific interactions, such as density-dependent disease. Additionally, pathogens contribute to equalizing mechanisms when they reduce differences in performance among species. Life history tradeoffs predict higher susceptibility to pathogens in rapidly growing species, which could equalize performance among fast- and slow-growing species in the presence of pathogens. 2. In a coastal prairie in California, we studied the impact of leaf diseases on the performance of seventeen coexisting species of Trifolium and Medicago (“clovers”). We transplanted clovers in randomized arrays into the natural prairie community in three years of common garden experiments. We quantified infection rates by isolating fungi from leaves, and we measured disease severity as percent leaf area damaged. In a fungicide experiment, we measured the impact of infection on biomass and survival. We assessed whether disease on transplants was positively related to natural abundance of that species in the surrounding community, which we monitored over 5 years. We assessed life history tradeoffs by testing whether more rapidly growing species were more susceptible to pathogens. 3. Rank abundance of clover species was stable over five years despite marked environmental fluctuations. Across hosts, fungal infection was not linearly related to density, although transplants of species that were locally absent showed lower and more variable infection. Disease severity was greater for more abundant species in only one of three years, and response to fungicide was not stronger in more abundant species. Faster-growing species experienced greater fungal infection. Consistent with predictions of the leaf economic spectrum, the impact of infection on faster-growing species was less negative than for slower-growing species. 4. Our results suggest that life history tradeoffs in plant-pathogen interactions may contribute to equalizing mechanisms among species in this guild, but that the combined effects of greater infection with greater tolerance may limit rather than promote coexistence. We also found modest evidence that density-dependent disease may contribute to stabilizing mechanisms. Lack of host specificity, rapid evolution of host use, and temporal variation in climatic conditions may all influence the role that pathogens play in coexistence of these closely related plants